L - Cochin University of Science and Technology

Certificate 

I hereby certify that the thesis entitled "Dynamics of Infaunal Benthic 

Community of the Continental Shelf of North-eastern Arabian Sea" submitted by 

K. A. Jayaraj, Research Scholar (Reg. No. 2269), National Institute of Oceanography, 

Regional Centre, Kochi -18, is an authentic record of research carried out by him under 

my supervision, in partial fulfilment of the requirement for the Ph.D degree of Cochin 

University of Science and Technology in the faculty of Marine Sciences and that no 

part thereof has previously formed the basis for the award of any degree, diploma or 

associateship in any university. 

Kochi-18 

22.03.06 

Dr. Saramma U. Panampunnayil 

Supervising Guide & Scientist -F 

National Institute of Oceanography 

Regional Centre, Kochi-18 

Kerala, India.

jf cronyms and jl66reviations 

AS 

ASHSW 

808 

CTD 

DO 

EEZ 

EICC 

et al. 

e.g. 

etc 

Fig. 

N 

NE 

NW 

NEC 

psu 

SW 

Sp. 

viz 

WICC 

St. 

Arabian Sea 

Arabian Sea High Salinity Water mass 

Bay of Bengal 

Conductivity - Temperature - Depth 

Dissolved oxygen 

Exclusive Economic Zone of India 

East India Coastal Current 

et alii (Latin word meaning 'and others') 

exempli gratia (Latin word meaning 'for the sake of example') 

et cetera (Latin word meaning 'and other similar things; and so on') 

Figure 

North 

Northeast 

Northwest 

North Equatorial Current 

Practical Salinity Unit 

Southwest 

Species 

videlicet (Latin word meaning 'namely') 

West India Coastal Current 

Saint

Contents 

Page No. 

Chapter 1. Introduction 

1. 1. The marine environment 

1.2. Benthos-definition & classification 3 

1.3. Importance of Benthos 5 

1.4. Review of literature 6 

1.5. Scope & Objectives 11 

1.6 References 

Cbapter 2. Materials and Metbods 

13 

2.1. Study area 20 

2.2. Collection of the samples 21 

2.3. Analytical methods 24 

2.4. References 

Cbapter 3. Hydrograpby 

28 

3.1. Introduction 33 

3.2. Results 37 

3.3. Discussion 42 


Cbapter 4. Sediment cbarecteristics 

46 

4.1. Sediment texture 56 

4.2. Organic matter 

4.3 References 

Cbapter 5. Standing stock 

65 

n 





Cbapter 6. Faunal composition and community structure 

\08 





Cbapter 7. Ecological relationsbips 

158 


7.2. Hydrography 194 

7.3. Sediment texture 200 

7.4. Organic matter 203 

7.5. Multiple regression analysis 206 

7.6. Trophic relationships 211 

7.7. References 21 5 

Chapter 8. Summary and Conclusion 239

1.1. The marine environment 

1.2. Benthos-definition & classification 

1.3. Importance of be nth os 

1.4. Review of literature 

1.5. Scope and objectives 


Chapter 1. 

Introduction 

The tenn "benthos" is derived from the Greek word meaning 'depth of the 

sea'. When organisms live in, or on are occasionally associated with aquatic 

sediments, their mode of life is referred to as benthic and collectively they fonn the 

'benthos'. According to Bostwick (1983), benthos are defined as those organisms 

live in or on the bottom of any water body. The benthic organisms play an important 

role in the marine food chain at the primary, secondary and tertiary levels. The 

demersal fishery especially in the coastal waters depends mainly on bcnthic 

productivity. As benthic animals lead a relatively sedentary mode of life, any change 

in the environment is reflected in the benthic organisms of the region. 

1.1. The marine environment 

The marine environment may be conveniently divided broadly into primary 

and secondary biotic divisions based either on physico-chemical attributes or on the 

nature of the biota (Sverdrup et al., 1942). lbe two primary divisions of the sea are the 

pelagic and the benthic realms. The fonner includes the entire water column while 

the latter includes all the ocean floor. 

Benthic division includes all the bottom terrain from water-washed shore line 

at flood-tide level to the abyssal depths. It supports a characteristic type of life that 

not only lives upon, but also contributes to and markedly modifies the characters of

the bottom. Ekman (1935) described the boundaries of the vertical zones from a 

geographic standpoint, and divided the benthic system into two, namely the littoral 

and the deep sea. The dividing line between these has been set at a depth of about 

200 m on the arbitrary supposition that this represents the approximate depth of water 

at the outer edge of the continental shelf and also roughly on the depth seperating the 

lighted zone from the dark portion of the sea. The littoral system is subdivided into 

the eulittoral and the sub littoral zones. The deep sea system is divided into upper 

archibenthic and lower abyssal benthic zones. The limits of the benthic subdivision 

are hard to define and are variously placed by different authors because uniform 

boundaries that fit all requirements cannot be drawn. For general biological studies, 

the different boundaries may be based on the peculiarities of the endemic plant and 

animal distributions and follow the region of most distinct faunal and floral change. 

The biotic zones thus delineated will be characterised by a more or less clearly 

defined range of external ecological factors which have given character to the 

population. 

The eulittoral zone extends from the high tide level to a depth of about 40 to 

60 m. The sublitttoral zone extends from this level to a depth of about 200 m, or the 

edge of the continental shelf. The dividing line bctween these subdivisions varies 

greatly between extremes, since it is determined by penetration of light. It will be 

relatively shallow in higher latitudcs and deep in the lower latitudes. In the upper part 

of the eulittoral zone a relatively well-defined tidal or intertidal zone is recognised. 

The benthic environment from shore to abyssal depths is covered, to a greater 

or lesser degree by sedimentary deposits that may be classified as terrigenous 

deposits, organic or pelagic oozes and red clay. As far as the biology of benthic 

animals is concerned, the most important feature of these oozes are their physical 

charastericts and the amount of digestible organic material they contain. Most deep 

sea benthic forms are detritus feeders and mainly dependent upon the rain of detrital 

matters of pelagic organisms that falls to the bottom. The production of pelagic food 

2

live at or near the bottom. Many Benthic organisms have the power to swim and can 

change their position, while some livc wholly or partially buried in the sediment and 

have limited ability to move around. They collectively form benthos or bottom 

communities. Benthos (both moving and sessile forms) represents a major 

component of the marine ecosystem and plays a vital role in the transfer of energy 

through food chain in the sea. Demersal fishes, crustaceans, molluscs, worms, 

echinoderms etc. are the larger forms coming under first category (moving forms). 

Sessile organisms are those, which stay at one place either fixed to the substrata or 

anchored at a suitable site. Corals, barnacles, encrusting sponges, anemones and 

seaweeds are sedentary in nature and belong to this group. However it must be noted 

that the distinction between pelagic and benthic is purely ecological and arbitrary as 

certain molluscs and crustaceans, living close to the bottom can adopt temporarily a 

pclagic mode of life. Larval forms of these organisms spent part of their life in the 

pelagic realm and are referred to as meroplankton. Three functional groups of 

benthos could be recognized namely the infauna, epibenthic fauna and hyper benthic 

fauna i.e., organisms living within the substratum, on the surface of the substratum 

and just above it, respectively (Pohle and Thomas, 2001). The infauna is much more 

restricted than the epifauna and only one-fourth as rich in species as the epifauna. 

The epifauna is represented by a maximum number of species in the tropical regions 

and they show decrease in number of species towards the poles. Based on the habitat, 

benthic organisms could be divided into two major groups namely soft-bottom 

benthos, and hard-bottom benthos. Depending upon the size, all large organisms 

retained by O.5mm (500J.l) sieve are generally referred to as macrobenthos; organisms 

which pass through a sieve of O.5mm but retained by 63J.l sieve are known as 

meiobenthos and those which pass through 63 J.l sieve are known as microbenthos. 

The dominant groups of organisms that constitute the macrobenthos are the 

sublittoral soft bottom inhabitants belonging to 4 major taxonomic groups 

polychaetes, crustaceans, molluscs and echinodenns. Among these, polychaete

wonns are the most abundant group and represented by numerous tube dwelling and 

burrowing species. Among meiobenthos, nematodes and foraminifers are the 

predominant ones. Other meiobenthic t'onns include harpacticoid copepods, 

ostracods, isopods, cumaceans, coelenterates, turbellarians and juveniles of larger 

invertebrates, gastrotrichs, kinorhynchs and tardigrades. The microbenthos include 

bacteria, protozoa, yeasts, fungi, diatoms, dinoflagellates, blue-green algae, 

euglenoids, crypomonads etc. (Mare, 1942). This distinction of benthos into three 

size categories is rather arbitrary and it has no biological significance and varies 

according to the researchers and also on the pore size of the sieve used. Demersal 

fishes, which browse and burry themselves in the sediment surface, are grouped as 

megafauna. All feeding types from selective feeders to carnivores and omnivores are 

represented in this group. Based on their trophic status benthos are classified as 

phytobenthos which are represented by plants and algae seen on the sea floor and 

zoobenthos which include all consumers. 

Of all the marine animals, a great many live on finn substrate, good numbers 

occur on sandy or muddy bottoms and a small percentage remains planktonic 

throughout their life. Benthic f'onns develop chitinous exoskeleton, calcareous shells 

and several other adaptations in the fonn of appendages and body musculature, 

enable them to live, move and propagate into the sediments or substrata they select to 

live. Animal representatives of most of the phyla are generally found in benthos, but 

a particular habitat is characterised by a few dominant species. 

1.3. Importance of benthos 

Estimation of benthic abundance is necessary for the assessment of demersal 

fishery resources, as the benthos fonn an important source of food for demersal 

fishes (Longhrust, 1958, Harkantra et al., 1980). According to Spark (1935) the 

average weight and number of benthic organisms have a correlation with primary 

production in the water column, climatic factors and also with demersal fish

production. Demersal fishery has a role in supporting the food requirements of man. 

Marine fish production in India showes that demersal finfish, crustaceans and 

molluscs together contribute about 49% of the total landings (CMFRI Anaual Report, 

1999). Besides their role in human diet, benthos especially mussels and clams are 

also used as an important centinel organisms for pollution monitoring studies and are 

being used as indicators of pollution. The main reason of choice of benthic organisms 

for pollution monitoring are that they have the ability to bioaccumulate many 

pollutants like heavy metals, hydrocarbons and pesticides. Their ability to metabolise 

pollutant is very low, so it is easy to measure the body load of pollutants and also the 

amount that is depurated. They are tolerant to wide ranges of temperature and 

salinity, and can be easily grown in captivity for experimental studies. They can be 

easily sampled from inshore areas due to their sedentary habit. 

Microbenthos are important since they are considered as the decomposers of 

the environment. They degrade the organic matter and enrich or get back the 

nutrients to the environment. Microphyto-benthos like diatoms are autotrophs and 

can prepare the food by means of photosynthesis. This food can be utilised by the 

meiobenthic forms. The meiobenthic organisms form the food for macrobenthic 

forms and act as a connecting link between the micro and macro forms, i.e primary 

producers and secondary consumers. Macrobenthic forms are later consumed by 

megabenthic forms like fishes and therefore the small benthic forms in turn regulates 

the demerasal fishery potential. 

1.4. Review of literature 

The major oceanographic efforts to study the organism and their environments 

initiated as expeditions under the leadership of differentr investigators using various 

research vessels from time to time. Italians, Marsigli and Donati were the first to 

study the benthos, using dredge around the year 1750 (Murray and I-Ijort, 1965). 

British - Anractic expedition in HMS Erebun and HMS Terror (1839-43) under the

leadership of Sir James Clark Ross, used a dredge showing that there was abundant 

and varied benthic fauna down to 730 m. The great marine expedition by H.M. S. 

Challenger (1872-76) during its coarse of study, made investigations on benthic 

invertebrates of the Pacific, Atlantic and Antarctic Oceans. The earlier works were 

on qualitative aspects and pioneering studies on the quantitative aspects of benthos 

were by Peterson (1911, 1913, 1914, 1915 & 1918) who developed a concept about 

community structure of benthos. Nicholls (1935) introduced the term 'interstitial 

fauna' to denote organisms, which inhabited the space between the sand particles. 

Remane (1940) coined the term 'mesopsammon' for these organisms and Thorson 

(1957) proposed 'isocommunity concept', which was the seed of vertical zonation in 

addition to Peterson's (1918) community concept. Sanders (1958) studied the 

benthos of Buzzards Bay and its positive correlation to the type of substratum. 

Sanders (1968, 1969) collected the benthos of the coastal and deep-sea areas and 

studied the population density and diversity of the organisms. Gerlach (1972) studied 

the bottom fauna and sediment characteristics and its influence on the burrowing 

resistance and filter feeding conditions. Buchanan et al., (1978) studied the temporal 

variations and observed that seasonal changes in abundance and biomass appeared to 

be independent of the composition of the assemblage. Gaston (1987) studied the 

feeding and distribution of polychaetes of Middle Atlantic Bight and found that 

proportion of carnivorous were greatest in coarse sediments and decreased 

significantly with water depth across the continental shelf. Graf (1992) investigated 

the benthic - pelagic coupling and developed an energy flow equation for marine 

sediments. Service and Feller (1992) whi le studying the sub-tidal macrobenthos from 

the sandy and muddy sites in the North inlet and noticed significant fluctuations in 

faunal abundance and high variability between replicate samples. 

Powelleit and Kube (1999) studied the effect of severe oxygen depletion on 

macrobenthos in the Pomeranian Bay and concluded that hypoxic and anoxic 

conditions have a major role in the distribution and abundance of be nth os. Desrosiers 

"/

et al., (2000) studied the trophic structure of Macrobenthos of Gulf of St. Lawrence 

and Scotian shelf using multivariate analysis and Martin et al., (2000) investigated 

the polychaetes and its spatial distribution and trophic structure of Alfacs Bay. 

Pioneering works on benthos in India were by Annandale (1907) on the 

macrobenthos and their ecology of Gangetic delta followed by Annandale and Kemp 

(1915) on the fauna of the Chilka Lake. Panikar and Aiyar (1937) studied the bottom 

fauna of the brackish waters of Madras and Samuel (1944) studied the animal 

communities of the Madras coast. Kurian (1953) and Seshappa (1953) studied the 

benthos of Trivandrum and Malabar coasts respectively while, Ganapati and Rao 

(1959) studied the benthos of the continental shelf of the north east coast of India. 

The Soviet research vessel 'Vityaz' collected samples during the Indian Ocean 

Expedition and the results has published by Beljaev and Vinogradova (1961) and 

Sokolova and Pasternak (1962). Later, Kurian (1967 & 1971) made an extensive 

study on the bottom fauna of the south west coast of India. A comparative study of 

marine and estuarine fauna of near shore regions of the Arabian Sea has done by 

Desai and Krishnankutty (1967) and Sanders (1968) studied the bottom fauna and 

species diversity along the east and west coast of India. Neyman (1969) made an 

extensive study on the benthos of northern Indian shelf and was the first study, which 

covered the entire length of northern Indian coast. The work on benthos of mud 

banks of Kerala coast was done by Damodaran (1973) and correlated the benthos 

with prawn fishery. He also included seasonal variations of macro and meiobenthos 

in his study, which was the first quantitative study on meiobenthos along the Indian 

coast. Ganapati and Raman (1973) investigated the role of Capitella capitata as an 

indicator species of Vis aka pat an m harbour. Parulekar and Wagh (1975) made studies 

on the quantitative distribution of benthic macrofuana of northeastern Arabian shelf 

and noticed a gradual decrease of biomass with depth and also in north-south 

direction. Parulekar et aI., (1976) have worked on the distribution and abundance of 

macro and meiofauna off Bombay in relation to the environmental characteristics.

Ansari et al., (1977b) carried out observations on the distribution of macrobenthos in 

five shallow bays of the central west coast of India and described the seasonal 

variations in benthic distribution. Ansari et al., (1977a) also conducted a study on 

the quantitative distribution of benthos in the depth range of 20-1700m from the Bay 

of Bengal and stated a clear relationship between type of sediment and density of 

animals. 

Harkantra et al., (1980) studied the distribution and abundance of benthos of 

the shelf region along the west coast of India and correlated a definite relationship 

between benthic biomass, organic carbon, nature of substrata and demersal fish 

catch. Divakaran et al., (1981) reported the distribution, abundance and ecology of 

benthic fauna from Vizhinjam harbour and its seasonal variations. Harkantra and 

Parulekar (1981) studied the qualitative and quantitative differences in the spatial and 

temporal distribution and production of macrobenthos during the pre-monsoon and 

post-monsoon seasons emphasising their rclation to the environmental factors in the 

coastal zone of Ooa. Parulekar and Ansari (1981) examined the benthic macrofuana 

of Andaman Sea and pointed out that distribution of macrofuana was substrate 

specific and environmental factors like temperature and oxygen also influence its 

distribution. Quantitative study on macro and meiobenthos and the relationship with 

demersal fishery resources in the Indian seas were done by Parulekar et al., (1982) 

and concluded that exploitation of demersal fisheries can increase without adversely 

affecting the resources. They also pointed out the decrease in the abundance of 

macrobenthos as depth increased and dominance of meiofuana in the slope and deep 

sea. 

Devassy et al., (1987) studied the effect of industrial effluent on biota off 

Mangalore, west coast of India and found that effluent discharge did not cause any 

noticeable damage to the inshore areas. Varshney et al., (1988) studied the qualitative 

and quantitative aspects of benthos of Versova (Bombay), west coast of India and 

stated that coastal areas were more polluted than off shore and high species diversity

indices of foraminifers and polychaetes In poHution stressed area revealed their 

tolerance to the pollutants. 

Harkantra and Parulekar (1991) using the multivariate analysis showed the 

dependence of distribution and abundance of sand dweHing fauna on more than one 

ecologically significant environmental parameters rather than one ecological master 

factor. Salinity, dissolved oxygen, grain size and availability of food together fonned 

significant factors in the distribution and abundance of be nth os. 

Vizakat et al., (1991) have made observations on the population ecology and 

community structure of sub-tidal soft sediment dwelling macro invertebrates of 

Konkan, west coast of India and postulated that sediment composition, organic 

carbon content of the sediment and salinity of the bottom water were the key factors 

determining the population and community structure. They observed an increase in 

faunal abundance from pre-monsoon to post-monsoon and suggested that 

colonization of shaHow water macrobenthic communities get enhanced with 

cessation of south west monsoon associated with stability of salinity in coastal 

waters. Prabhu et al., (1993) observed significant spatio-temporal variations in the 

qualitative and quantitative distribution of benthos in the nearshore sediments ofT 

Gangolli, west coast of India. 

Ansari et al., (1994) made a survey of the macro invertebrate fauna in the soft 

sediment of Mormugao harbour and revealed the spatial heterogeneity based on the 

environmental parameters and benthic assemblage. Harkantra and Parulekar (1994) 

also stressed the monsoon impact, which plays an important role in the density and 

diversity of soft sediment dweHing macrobenthos of Rajapur Bay, west coast of India 

and its replenishment after the monsoon. Ansari et al., (1996) studied the macro and 

meiobenthos of the EEZ ofIndia and pointed out the relevance ofbenthic data in the 

assessment of potential fishery resources. 

Saraladevi et al., (1996) studied the bottom fauna and sediment 

characteristics of the coastal regions of southwest and southeast coasts of India. 

I()

Gopalakrishnan and Nair (1998) conducted study on the sub tidal benthic macro 

fauna of the Mangalore coast, west cost of India and found the dominance of 

molluscs over polychaetes in the study area and also pointed out the increase in 

benthic abundance as moving towards greater depths (5 m to 15 m). Sheeba (2000) 

studied the distribution of benthic infuana in the Cochin backwaters, the south west 

coast of India in relation to the environmental parameters and Joydas and Damodaran 

(2001) studied the diversity and abundance of macrobenthic polychaetes along the 

shelf waters of west coast of India. Ingole et al., (2002) have done a study on the 

macrobenthic communities of the coastal waters of Dabhol and suggested that coastal 

waters of Dabhol provide favourable environmental conditions for feeding and 

breeding of commercially important prawn and crab species. Joydas (2002) studied 

the macrobenthos of west coast of India. 

Quantitative studies on meiofauna from west and east coast of India were 

taken up by Thiel (1966), Mc Intyre (1968), and Sanders (1968); and central Indian 

Ocean by Ingole et al., (2000) and Sommer & Pfannkuche (2000). Works of 

meiobenthos from the west coast were that of Damodaran, 1973;Ansari et aI., 1977a, 

1980; Ingole et al., 1992; Ansari and Parulekar, 1993). Pollution and its impacts on 

meiofauna were reported by many workers (Varshney, 1985; Rao, 1987, Ingole et al., 

2000). Sajan (2003) studied the meiobenthic fauna of the west coast oflndia. 

1.6. Scope and objectives 

Benthic studies in India were rather neglected till 1970 due to lack of 

infrastructure and the laborious nature of the work, though scattered attempts had 

been made to understand the quantitative nature and community structure of benthos 

from different regions (Kurian, 1953& 1967; Neyman, 1969). Later, many workers 

(Neyman et al., 1973; Kurian, 1971; Damodaran, 1973; Parulekar, 1973; Parulekar 

and Wagh, 1975; Parulekar et al., 1976; Ansari et al., 1977 a&b; Ansari et al., 1980; 

Harkantra et al., 1980) reported on benthos and most of the information pertains to 

1 I

egional studies on macrobenthos. Damodaran (1973) and Harkantra et al., (1980) 

have attempted to correlate the benthic standing crop as an indication of the potential 

resources of demersal fish and the prawns. 

Most of the earlier studies were directed towards the qualitative and 

quantitative aspects, but during the beginning of the present century, interest in the 

benthos has been directed more on the ecology, with particular reference to benthos 

as a source of fish food. Since 1973, National Institute of Oceanography has 

collected extensive data on various aspects of bottom organisms in different regions 

of the Indian Ocean and some of the results have already been documented 

(Parulekar, 1973; Parulekar and Wagh, 1975; Parulekar et al., 1976; Ansari et al., 

1977 a&b; Ansari et al., 1980). Most of the studies pertaining to the seasonal changes 

on benthos were in the estuaries and backwaters and a few in the shallow subtidal 

regions of west coast (Ansari et al., 1977a; Harkantra and Parulekar, 1981; Vizakat et 

al., 1991, Prabhu et al., 1993; Harkantra and Parulekar, 1994; Gopalakrishnan and 

Nair, 1998) and all are from the very shallow coast of 5-20 m depth. However no 

attempt has been made to project the role of environmental factors on the benthic 

community structure and their distribution and abundance off the coast between 30- 

200m except that of Joydas (2002), which lacks any seasonal comparison. The 

northern part of Indian Ocean is peculiar with its land locked water body, which 

separates the Indian Ocean from the other two major oceans. The northwest coast of 

India experiences different climatic changes under the influence of monsoonal 

regime. Winter cooling is a special feature observing in the study area. It is therefore 

necessary to investigate various environmental factors and their role in structuring 

the infaunal benthic community, variation in their biomass, population density. With 

this view the present study was taken up to investigate the seasonal changes in the 

northwest coast of India and its impact on benthic organisms and the key factors that 

controls the benthic production.

Major objectives:- 

1. To understand the distribution and abundance of marine benthos in relation to 

the prevailing environmental conditions. 

2. To evolve latitudinal and depthwise variations of be nth os. 

3. To assess the community structure, species composition and diversity of 

benthic organisms. 

4. To evaluate hydrography and the sediment characteristics of the northeastern 

Arabain Sea and its influence on benthic community. 

13


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Oopalakrishnan, T. C., Nair, K. K. C., 1998. Subtidal benthic macrofauna of the 

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approach. Indian 1. Mar. Sci. 20, 232-234. 

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Mar. Georesour. Geotechnol. 18(3),263-272. 

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2.1. Study area 

2.2. Collection of the samples 

2.2.1. Hydrographic parameters 

2.2.2. Sediment and benthic samples 

2.3. Analytical method\· 

2.3.1. Sediment texture 


2.3.2. Organic carbon 

2.3.3. Benthic samples 

2.3..1. Statistical analysis 

2.1. Study area 

2.3.4.1. Community structure 

2.3.4.2. Similarity index 

Chapter 2. 

Materials and Methods 

2.3.4.3. Predictive multiple rewession models 

The area selected for the present study is the continental shelf of the northwest 

coast of India. Samples were collected onboard the Fishery and Oceanographic 

Research vessel (FOR V) Sagar Sampada (Plate 1) as part of benthic productivity 

studies of a multidisciplinary project 'Marine Research on Living Resources (MR 

LR) Progamme', funded by Department of Ocean Development (000), Govt. of 

India through the Centre for Marine Living Resources and Ecology (CMLRE). The 

present study is based on the samples collected along 6 transects (October, 1999) and 

5 transects (February, 2002). 

22

analysed after acidification by titration against standard sodium thiosulphate using 

starch as indicator. The concentration of oxygen in the sample was calculated as, 

Dissolved oxygen (mill) = 5.6*N*(S-Bm)* VI V-l)*lOOOIA 

Where. 

N = Normality of thiosulphate in solution 

S = Titre value for sample 

Bm = Mean titre value for blank 

V = Volume of the sample bottle 

2.2.2 Sediment and benthic samples 

A = Volume of sample titrated (50 ml) 

Sampling was done for the estimation of sediment parameters like texture and 

organic matter and for macro and meiobenthos from all the stations. A total of 48 

grab samples (23 from post-monsoon season and 25 from pre-monsoon season 

cruises) were collected for the present work. Modified Smith Mc lntyre Grab was 

used for collecting sediment samples (Plate 3). It traps a substantial volume of 

sample, as its open mouth covers a surface area of 0.lm2. During the sampling. the 

vessel was maintained stationary and the wire was kept as vertical as possible to 

ensure vertical set down and lift-up of the grab at right angles to the hottom. As 

recommended (ICES, 1994). the final 5 m of descent was maintained at a rate < 0.5 

m.s- I 

to minimize the shock bow wave disturbances. The sample showed a 

distinguishable undisturbed surface layer. often including loose flocculent deposits 

and no sign of sediment leakage, such as from incompletely closed buckets. 

Approximately 150 gm of wet sediment sample from each station was taken and 

dried onboard the ship at 70° C in an oven and stored in the polythene bags for the 

study of sediment characteristics. The dried samples were taken to the laboratory for 

further analysis. 

24

2. 2. 2. 1. Macrobenthos 

After sub sampling, all the samples remaining in the grab were sieved through 

O.5mm (SOO J!) sieve to separate specimens from the substrate. For unloading the 

sediment from the grab and then sieving, a wooden platform was fabricated (Plate 4). 

The sediment was unloaded in the conical aluminum portion of the platfonn, which 

was attached to the upper frame. The lower frame was modified in such a way so as 

to slide in and out the sieve in the form of a drawer, where the sediment unloaded as 

directly collected in the sieve. For the present study, O.S mm sieve was selected for 

separating macro benthos. 

In order to avoid sample degradation, the sieving was accomplished on board 

soon after the sample collection. It was done by washing the sample with seawater in 

a bucket and then sieving using SOOJ! sieve. Since immediate processing for 

taxonomic study is not possible, sieved specimens and residual sediments were 

transferred to plastic bottles and fixed in S% neutral fonnaldehyde with "Rose 

Bengal" for staining the live organisms. Samples were properly labeled with details 

like cruise number, date, time, station position and depth. 

2.2.2.1. Meiobenthos 

At each station, with the help of a glass corer (2.S cm diameter), sediment 

samples of 10 cm long cores were drawn and length of the core measured. Replicate 

(in some cases only one) sub samples were collected from each haul. The samples in 

Toto were transferred to polythene containers, labeled and material preserved in 70% 

alcohol-Rose Bengal solution for further examination. 

On arrival at the shore laboratory, the sediment samples were processed 

through a set of two sieves, the upper one of SOOJ! and the lower with 63Jl. Residue 

retained over 63 J! sieve was back washed into a glass container and the same 

preserved in 70% alcohol or 4% neutral formalin. In some cases, Rose Bengal was 

25

used as stain prior to sorting and enumeration. The general methodology was that the 

residue over 63 Jl sieves was taken into a 1000 ml beaker and filled with filtered 

seawater. The diluted sample was elutriated. The supematant was passed through a 

63Jl sieve. The meiobenthods retained on this sieve was washed into a 250 ml glass 

beaker. Meiobenthos in the aliquot sample was then enumerated group wise using a 

binocular microscope. The total number of organisms in the sample represented by 

different groups was calculated and expressed as number/lOcm 2 • Biomass of 

meiobenthos (mgll0 cm 2 ) was determined by using a high precision electronic 

balance (eg. Sartorius). 

2.3. Analytical methods 

2.3.1. Sediment texture 

In the laboratory. for the analysis of sand. silt and clay. oven dried sediment 

samples were subjected to pipette analysis according to a standard method 

(Krumbein and Petti John. 1938). The percentage of each grade (sand. silt. clay) was 

calculated and plotted as triangular graph based on the nomenclature suggested by 

Shepard (1954) 

2.3.2 Organic carbon 

Organic carbon in the sediment was estimated by wet oxidation method (EI 

Wakee1 and Riley, 1957). which was then converted into organic matter (Trask, 

1939). For this. salt was removed by repeated washing. It was done by thoroughly 

mixing the sediment sample with fresh water in a 500 ml beaker and keeping the 

sample for one day for settling and decanted the supematant. Repeated the process 

till all the content was removed prior to the estimation. 

26

2.3.4.1 Community structure 

PRIMER (Plymouth Routines In Multivariate Ecological Research) V 5 

software package developed at Plymouth Marine Laboratory (Clarke and Warwick, 

1994; Clarke and Gorley, 2001) for windows (version 5.2.8) was used for the 

estimation of community structure. Diversity indices such as Margalef s index for 

species richness (Margalef, 1968). Shannon index for species diversity (Shannon and 

Weaver, 1963), Heip's index for evenness (Heip, 1974) and Pielou's index for 

dominance (Pielou, 1966) were computed separately for polychaetes and for all the 

groups together including polychaetes. Indices used for the community structure 

analysis are given below. 

Species richness, d = (s-1 )/LOgIO (N) 

Shannon H(s) = -L:(Pi Log:! Pi) 

j=1 

Heip's evenness J' = e'l( s l-l/s_1 

}=s 

Pielou's dominance = H(s)lMax H(s) 

2.3.4.2. Similarity index 

Similarity between stations with respect to polychaete species and all groups 

combined together were calculated using PRIMER V 5 for windows (version 5.2.8). 

For this Bray-Curtis similarity index (Bray and Curtis, 1957) with fourth root 

transformation was adopted. Dendrogram was plotted using the group average cluster 

mode for grouping stations with respect to polychaete species and also with respect 

to all groups including polychaetes. 

2.3.4.3. Predictive multiple regression models 

Abundance can be related to the environmental parameters by means of linear 

regression. But this relation gives only the prediction efficiency of a single factor at a 

time. A number of factors are jointly controlling the bioactivities at a point of time or 

2B

space. Therefore, it is very essential that, the quantification parameters be considered 

simultaneously to have the best predictive model. Pedersen et al., (1995) have given 

a method for choosing the minimal set of environmental variables that explain the 

variation in the plankton data. Here, an attempt has been made to choose the best 

predictive model (Jayalakshmi, 1998) from a set of 2k predictive models containing 

individual factor effects and first order interaction effects where 'k' is the number of 

parameters used as the independent variables. Using explained variability as the 

criterion for selecting the best model (Snedecor and Cochran, 1967), the factors 

influencing the benthic productivity in terms of biomass and density has been 

determined.


Bray, J. R., Curtis, J. J., 1957. An ordination of the upland forest communities of 

southern Wisconsin. Ecol. Monogr. 27, 325-349. 

Clarke, K. R., Gorley, R. N., 2001. PRIMER v 5 User Manual. Preimer-E, Plymouth, 

9lpp. 

Clarke, K. R., Warwick R. M., 1994. Change in marine communities: an approach to 

statistical analysis and interpretation. Plymouth Marine Laboratory, 1-144 pp. 

Day, J. H., 1967. A monograph on the polychaetea of southern Africa, Part I and H. 

Trustees of the British Museum (National History), London. 

EL Wakecl S. K., Riley J. P., 1957. Determination of organic carbon in marine mud. 

J. Cons. Perm. 1nl. Explor. Mer. 22,180-183. 

Fauval Pierre, 1953. The fauna of India including Pakistan, Ceylon, Burma and 

Malaya- Annelida, Ploychaeta. The Indian Press Ltd. 

Gosner L. Kenneth, 1971. Guide to identification of marine and estuarine 

invertebrates. John WiIey & Sons, Inc. 

GrasshofT, K., 1976. Methods of sea water analysis, Verlag Chemie, Weinheim, 260 

pp. 

i-Icip, C., 1974. A new index measuring evenness. Mar. Bilo. Ass. (U.K), 54, 555·· 

557. 

ICES, 1994. Quality assurance of guidelines for benthic studies. International 

Council for Exploration of the Seas, Report of the Benthic Ecology Working Group, 

92-94 pp. 

Jayalakshmi, K. V., 1998. Biometric studies on the trophic level relation in the Indian 

Ocean. Ph. D. Thesis, Cochin University of Science and Technology 484 pp. 

Krumbein, Petti John, F. J., 1938. Manual of Sedimentary Petrography Appleton 

Century Crafts, New York, 549 pp. 

Margalef, R., 1968. In: Perspectives in ecological theory. Univ. Chicago Press, III 

pp. 

3G

Fig. I - Station locations 

32

Plate1 

Plate 2 

Plate 3 

Plate 4

affected at high temperature. Most marine organisms do not regulate their body 

temperature (Poikulotherms). Temperature effects within lethal extremes thus have 

great effect on biochemical reactions and metabolism. 

Temperature affects the rate of metabolic processes and apparently affects 

morphology of organisms. Warmer temperature, within limits, generally enhances 

metabolic and behavioral activity. The relationship of temperature to metabolic rate 

causes conspicuous physiological problems for marine species that live in thermally 

varying seasonal environments. Cold winter temperature can depress activity of 

poikulotherms with no capacity for acclimation. In tropical fishes, cold depression of 

respiratory system can lead to anoxic condition and death. Many invertebrate species 

spawn only when an optimum temperature is reached. Seasonal changes in gamete 

synthesis and liberation are highly correlated with temperature. The lower solubility 

of oxygen at higher water temperature might limit the individual's capacity for 

efficient respiration and may also limit the distribution of organism. The cause of 

heat death in some cases may be due to protein denaturation or thermal inactivation 

of enzymes. Tolerance of temperature is an important factor regulating the 

distribution of marine organisms. Thus temperature is a major factor regulating the 

distribution and abundance of marine organisms. 

Salinity ranges from 33 to 38 psu in the open ocean. In the open ocean, 

salinity is increased by evaporation and sea ice formation and decreased by dilution 

processes, such as rainfall and river run off. In the coastal waters more drastic 

variation in salinity is observed because of influence of river input. Salinity change 

can present problems to marine organisms because of the physical processes of 

diffusion and osmosis (Levinton, 1982). When salinity changes, marine organisms 

face the danger of water loss or gain, with concomitant changes in body volume. 

Effect of salinity is more in the nearshore waters and estuaries where severe 

fluctuation in salinity is observed due to fresh water influx.

The distribution of oxygen in the ocean is controlled through the exchange 

with the atmosphere and the bioiogical processes of photosynthesis and respiration. 

Oxygen from the atmosphere dissolves in seawater at the sea surface. The amount 

that can be dissolved decreases gradually with increasing temperature and to a lesser 

extent, with increasing salinity. Amount of organic matter present in the system also 

influences the availability of oxygen. Particulate organic matter sinks down and 

accumulates on the density gradient generated by the thermocline. Bacteria 

breakdown this debris and consume oxygen in the process, thereby producing oxygen 

minimum layers (Levinton, 1982). Almost all eUkaryotic organisms require oxygen 

for metabolism. The continued absence or even depletion of dissolved oxygen (DO) 

results in lowering of metabolic activity. Active species consume more oxygen than 

inactive species. Sponges, ascidians and most bivalves consume much less oxygen 

than decapods, cephalopods and teleosts. Species actively feeding during day require 

more oxygen. Oxygen dissolved in water plays a significant physical as well as 

biochemical role in the life of aquatic organisms. The oxygen - hydrogen sulphide 

system is responsible for the development of oxidation-reduction potential. This 

system begins to operate when the oxygen is depleted, mostly due to the presence of 

large amount of organic matter associated with effective vertical separation of the 

water masses. Under anaerobic condition, bacteria, which use the oxygen bound in 

sulphide for oxidation of their organic nutrients, develop, with concomitant formation 

of gaseous H2S, which dissolves in the seawater. As H2S is a powerful biological 

poison, normal plant and animal life can no longer be sustained in such regions. In 

certain fine sediments, anaerobic conditions may develop and effectively exclude 

many species requiring a good supply of oxygen (Fincham, 1984). However, many of 

the meiobenthic forms thrive in this deoxygenated condition. 

Arabian Sea (AS) is unique among the low latitude seas because it is land 

locked in the north by Asian landmass and has marked continental influence. It 

experiences seasonal reversal of atmospheric forcing, and consequently the upper 

35

layers exhibit different oceanographic characteristics during different seasons. The 

ecosystem is very much influenced by seasonal winds, thennohaline circulation and 

remote forcing. Enhanced evaporation is a peculiarity of the AS. The coastline is 

surrounded by the large landmasses, which enhance the differential heating. The land 

has a lower capacity to maintain heat that of water. Therefore, a strong land-ocean 

thermal gradient develops in this region, causing monsoon. As has an extensive bund 

of oxygen minimum layer which often surfaces in coastal areas during the period of 

upwelling. 

Hydrographical studies along the western continental shelf were limited till 

the International Indian Ocean Expedition during 1960 to 1965. During the northeast 

monsoon (Nov-Feb), the winds in the coastal regions of the western India are 

northerly but currents flow pole ward (Darbyshire, 1967). Coastal current along the 

east coast of India (East India Costal Current, EICC) flows equator wards, which 

carries low saline Bay of Bengal (BOB) waters, turn round Sri Lanka and continue to 

flow towards north as West India Coastal current (WICC) along the west coast of 

India and supllies low salinity water in the southern AS. In the northern AS, cool and 

dry continental air brought by prevailing northeast trade winds intensifies the 

evaporation leading to surface cooling. This combined with reduced incoming solar 

radiation and high amount of salinity drives convective mixing in the northern AS, 

that leads to the injection nutrients into the surface layers from thennoc1ine 

(Bhattathiri et al., 1996). The evaporative cooling and convection leads to the 

formation of Arabia Sea High Saline Water Masses (ASHSW) in the northern AS. 

During intermosoon fall under wann and light wind condition, the surface layer 

becomes more stable which inhibits vertical mixing leading to the thinning of mixed 

layer. Under these conditions, entrainment of nutrients to the surface is not possible 

and as a result nutrient depleted layer deepens and eventually leads to poor 

production. 

36

The continental shelf along the west coast of India comes under the monsoon 

regime and hence undergoes seasonal reversal with its hydrography and circulation. 

During southwest (summer) monsoon, the coastal current, WICC along the western 

shelf is towards south while in NE monsoon (winter monsoon) it is towards north. 

This type of reversing pattern of circulation is unique to the northern Indian Ocean. 

Upwelling which brings nutrients to the surface layers in the western shelf during 

SW monsoon supports high biological productivity is also a peculiar feature observed 

in the AS. 

3.2. Results 

Variations of environmental characteristics in the bottom water of the 

northwest continental shelf of India are examined in this chapter. Temperature, 

salinity and dissolved oxygen in various depth zones along different transects have 

been analyzed in this section in three parts. The first part deals with results of 

hydrographic features of the post-monsoon season, second part describes the same 

during pre-monsoon season, the third part deals with the seasonal comparison. 

3. 2.1. Post-monsoon 

Depth wise and transect wise variations of environmental factors during post 

monsoon season are presented here. 

3.2.1.1. Temperature 

Depth wise distribution bottom water temperature in the study area is presented 

in Fig. 2a-f. During post-monsoon, temperature generally decreased to deeper depths 

from 30 m onwards at all transects. Off Mormugao there was a gradual decrease in 

temperature towards deeper depths, but the variation at different depths was low. OfT 

Ratnagiri, Mumbai, Veraval and Porbandar also a decrease in temperature was 

observed from shallow to deeper depths. Off Dwaraka, only two stations were 

sampled and high value was observed at shallow station. 

37

Transect wise variation in temperature distribution along different depth zones 

is presented in Fig. 3a-f. A gradual increase towards northern latitude was noticed at 

30 m zone. At 50 m zone temperature fluctuated between transects with lower values 

in the southern transect and higher values in the northern transect. From 75-150 m 

zone also temperature fluctuated along different transects. At 75 m zone, highest 

value was observed off Veraval and lowest value off Mumbai. At 100 m zone, 

comparatively high values were noticed off Veraval and Dwaraka and low values in 

the southern transects especially off Mumbai. At 150 m zone, low temperature was 

observed off Ratnagiri and slightly high temperature off Porbandar and then it 

decreased towards off Dwaraka. In general, the observations indicated lower 

temperature in the southern latitude stations and higher values in the northern latitude 

stations. 

3.2.1.2. Salinity 

Depth wise distribution of bottom water salinity along different transects is 

shown in Figurs 4a-f. Off Mormugao a slight increase was noticed upto 75 m 

followed by a slight decrease to deeper station. Off Ratnagiri also salinity increased 

slightly to deeper depth up to 75 m and after that a decrease was noticed. Off 

Mumbai, a general decrease was noticed to deeper areas. Off Veraval and Porbandar 

also a gradual decrease was noticed towards deeper stations. Off Dwaraka, only 2 

observations were made and high salinity was observed in both stations with 

comparatively high value in deeper station. Generally, in southern transects ofT 

Mormugao and Ratnagiri, salinity increased to offshore and rest of transects had high 

salinity in shallow stations which decreased to deeper zone. Transect wise variation 

in various depth zones showed a gradual increase towards northern latitude at all 

depth zones (Figurs Sa-e). 

3.2.1.3. Dissolved oxygen (DO) 

Depth wise distribution of bottom water dissolved oxygen (hereafter referred to 

as DO) in the study area is presented in Figurs 6a-f. Off Mormugao, generally a 

3B

was observed upto 75 m and then decreased to deeper depth zone (150 m). The 

decrease was more at 75 m to 100 m depth zone. 

Transect wise variation in temperature distribution (Fig. 3a-t) showed that 

southern transects (off Mormugao and Ratnagiri) recorded high values and northern 

transects (OfT Veraval and Off Dwaraka) recorded low values. Generally 

temperature decreased towards north. The temperature difference between southern 

most and northern most stations in each depth zone showed that it was maximum at 

75 m zone (3.87 QC) and minimum at 150 m zone (0.83 Q C). In 30 m, 75 m and 150 m 

zones, the decrease was gradual but at 50 m and 100 m depth zones decrease was not 

so gradual with slight increase off Dwaraka. At 200 m depth, only 2 observations 

were made and the temperature decreased from off Mumbai to Veraval. 

3.2.2.2. Salinity 

Bottom water salinity distribution in the study area is presented in Fig. 8f-j. In 

general, salinity was high in the study area with low values in the shallow stations of 

the southern transects (off Mormugao, Ratnagiri and Mumbai). An increase was 

observed to greater depths off Mormugao, off Ratnagiri and ofT Mumbai while no 

marked variation was observed ofT Veraval. High values with fluctuating trend was 

noticed off Dwaraka. 

Transect wise variation of salinity in difTerent depth zones (Fig. 5a-t) showed 

that at the 30 m zone there was a gradual increase of salinity towards north with 

minimum values ofT Mormugao (35.09 psu) and maximum off Dwaraka (36.12 psu). 

At 50 m zone also a gradual increase was observed towards northern transects. At 75 

m zone, salinity showed a gradual increase from ofT Mormugao towards north with 

exceptionally high value otT Ratnagiri. At 100 m zone, fluctuating trend was 

observed with low value ofT Veraval (35.74 psu) and high value ofT ofT Dwaraka 

(36.36 psu). At 150 m zone, salinity did not vary much and low value was observed 

otTVeraval (35.72 psu) and high value ofT Dwaraka (35.89 psu). At 200 m depth, 2 

observations were made, salinity decreased from offMumbai to Veraval. 

40

3.2.2.3. Dissolved oxygen (DO) 

Distribution of bottom water DO in the study area is presented in figurs 8k-o. 

Generally DO showed a sharp decrease towards deeper depths in the study area. 

Along Monnugao transect DO showed a decrease to deeper stations. Off Ratnagiri, 

high DO values were observed at all stations and the pattern of distribution was same 

as that observed off Monnugao. OLT Mumbai, a general trend of decrease was 

observed except at 75 m depth where a slight increase was noticed. OfT Veraval and 

Dwaraka also, the decreasing trend was observed towards deeper depths. Generally 

higher values were observed up to 75 m and the gradient increased from shallow to 

deeper depths. 

Transect wise variation of DO distribution in various depth zones (Fig. 7a-f) 

showed that at 30 m, 50 m and 75 m zones, a gradual increase was observed from 

south to north. At 100 m zone, a fluctuating trend was noticed with low value off 

Vcraval and high value off Dwaraka. At 150 m zone generally low values were 

observed and as an exception from the previous depth zones here DO showed a 

decreasing trend towards north. Beyond 150 m, 2 observations were made and off 

Mumbai recorded high DO (0.6ml/l) and off veraval recorded low value (0.16ml/l). 

Generally in the shallow depth zones of 30 to 75 m there was a northward increase in 

DO values while at 150 m zone, a reverse trend was observed. 

3.2.3. Seasonal comparison 

Seasonal variations were very conspicuous in the study area. Temperature 

during post-monsoon decreased to deeper depth stations in all transects while during 

pre-monsoon it increased initially and then decreased to deeper depths. During post 

monsoon, temperature increased to north while during pre-monsoon a northward 

decrease was noticed and the average temperature in the whole study area was high 

during pre-monsoon compared to post-monsoon. Salinity distribution, during post 

monsoon period showed an increasing trend towards deeper depths only ofT 

41

Monnugao and Ratnagiri and along other transects it decreased towards deeper 

depths. During pre-monsoon season salinity increased to deeper areas in the southern 

transects otT Mormugao, Ratnagiri and Mumbai and no such trend in the northern 

latitude stations was observed. Both seasons exhibited northward increasing trend in 

salinity distribution. DO generally decreased to deeper areas in both seasons with 

some exceptions. Latitudinal northward increase of DO was only at 50 m and 75 m 

zones during post-m on soon season while during pre-monsoon in almost all depth 

zones northward enhancement in the level of DO was observed. But in the 150 m 

depth zone DO was low in the northern latitude station. Average DO in the study area 

was high during pre-monsoon season (2.69mlll) compared to post-monsoon 

(O.22ml/l). 

Student's t statistical analysis showed that temperature and DO showed 

significant seasonal variations (Table 1). At 30 m depth, temperature and DO have 

high significant difference between the two seasons (t=2.3916, p

monsoon temperature initially increased then decreased to deeper depths. Qasim 

(1982) has also noticed a decrease of temperature from south to north during pre 

monsoon season in the northern Arabian Sea. The winter is more pronounced in the 

northern region of the Arabian Sea (AS) than southern region as it is away from the 

equator (Darbyshire, 1967). This must be the reason for the decrease in temperature 

from south to north during pre-monsoon season. In general, cooling from south to 

north and low temperature in the coastal waters (up to 75 m) may be because of the 

cooling of the land mass in the northern region and a general flow of cold air from 

the land causing more cooling of the sea close to the land (Sankaranarayanan, 1978). 

This may be the reason for the low temperature in the shallowest region. Joydas 

(2002) also noticed a decrease in bottom temperature with depth and latitude. The 

high values in shallow regions and low values in deeper stations during post 

monsoon season may be due to the secondary heating during this period. In this 

season, no cooling of landmasses is taking places as that of pre-monsoon season. 

Salinity showed a general trend of increase towards north at all depth zones 

during post-monsoon but during pre-monsoon, northward increase was obvious only 

in shallow depth zones (30 m and 50 m). In other depth zones, salinity values 

fluctuated with relatively low values in southern transects and high in northern 

transects. The high rate of evaporation results in the fonnation of several high saline 

water masses. The general northward increase during post-monsoon season may be 

attributed to the presence of Arabian Sea High Saline Water (ASHSW) (Qasim, 

1982). The Arabian Sea high saline water, fonned in the northeastern AS, can be 

traced as a tongue of high saline water towards south (Qasim, 1982). Low surface 

salinity of the west coast of India south of 20° N might be due to the inflow of low 

saline water from the south and not due to either rainfall or land run off as no major 

rivers enter this area and the rainfall in the region is quite low (Qasim, 1982). The 

southern low saline water indicates the presence of north equatorial current (NEe) 

which carries the low saline waters along with it from the Bay of Bengal (BOB) and 

43

the eastern Indian Ocean into the western AS during this season. During the northeast 

monsoon (pre-monsoon season of the present study). low saline water from the BOB 

joins the northward flowing equatorial Indian Ocean water and flows as a northward 

surface current along the west coast of India (Pankajashan and Ramaraju. 1987). The 

reduced salinity in the shallow depth zones also shows the presence of BOB waters, 

which is coming from BOB to AS through the coastal current (Darbyshire, 1967, 

Wyrtki. 1971). Kumar and Mathew (1997) noticed that the maximum northward 

extension of this low saline water is upto 12° N in January but could be traced upto 

17° N in February- March. It starts retreating from March onwards and coincides 

with the reversal in the upper layer circulation. Kumar and Prasad (1996) reported a 

weakly stratified layer of high salinity in the north, thinning towards south in the 

northern AS. They also added that very low saline water towards the south indicates 

the influence of BOB waters, being carried along the shelf by the northward flowing 

coastal current. Joydas (2002) pointed out that the low saline condition in the 

nearshore region could be attributed to the river discharge. In the present study, 

deeper waters of southern transects (off Ratnagiri and Mumbai) showed an increase 

in salinity during both seasons. This increase may be due to the presence of ASH SW. 

The core of ASHSW seen below the surface in the north deepens while spreading 

towards south, which may cause the increased salinity in the south. 

DO was found to increase from south to north in shallow depth zones (30 m 

and 50 m) and the trend got reversed in deeper zone (I50 m) during pre-monsoon 

season. DO showed fluctuating trends in between these zones (75 m and 100 m). 

Generally low values were observed during post-monsoon as compared to pre 

monsoon. During both seasons DO decreased to deep in all transects. Qasim (1982) 

reported a distinct decrease from inshore to off shore. Moreover it decreased towards 

north in the deeper areas of 150 m zone as observed by Joydas (2002). This depletion 

of oxygen in the shelf edge of northern latitudes may be associated with the oxygen 

minimum layer described by Gupta et al., (I 976b, 1980) and Qasim (1982). They 

44

opined that limited mixing. high organic production. sinking and decomposition of 

large amount of organic matter were the reasons for this oxygen depletion in higher 

latitudes. Ivanenko and Rozanov (1961) have reported the presence of H 2S in the 

oxygen deficient zones of AS and BOB. Nejman (1961) observed sinking of high 

saline. high temperature. oxygen poor water in the Persian Gulf and Gulf of Aden 

and spread into the subsurface layers which may have its influence on the low 

oxygen and high saline water observed in the northern transects. Rao and Jayaraman 

(1970) suggested that the oxygen minimum is because of near stagnant conditions in 

the north and central parts of the AS. According to Wyrtki (1973) the oxygen 

minimum layer is due to the isolation and stagnation of the intennediate water. 

limited horizontal advection and high primary productivity. 

The distribution of DO in the northern Indian Ocean is different from most of 

the other open ocean areas in that the surface layer is well mixed down to the 

thennocline and oxygen maximum could occasionally be observed within this layer, 

especially during pre-monsoon season. The intensity of the incident solar radiation is 

very high during this period. which causes maximum primary production to occur a 

few meters below the sea surface (Qasim. 1977). This together with high vertical 

stability may result in the observed oxygen maximum in the shallow depths. The 

strong density gradient prevent any significant exchange of DO from the euphotic 

zone to layers below the thennocline. and the horizontal advection is poor due to the 

semi enclosed nature of the region. These features in conjunction with a high rate of 

supply of organic matter from the surface result in a severe depletion of DO below 

the thermocline throughout the northern Indian Ocean. a feature recognjzed by 

several workers (Nejman. 1961, Wyrtki, 1971. 1973. Gupta et al .• 1976a, 1976b, 

Naqwi et al .• 1982). 

45


Bhattathiri, P. M. A., Aditi Pant, Surekha Sawant, Gauns, M., Matondkar, S. G. 

P., Mohanraju, R., 1996. Phytoplankton production and chlorophyll distribution 

in the eastern and central Arabian Sea in 1994-1995. Curr. Sci. 71(11), 857-862. 

Darbyshire, M., 1967. The surface waters off the coast of Kerala. Deep Sea Res. 

14,295-320. 

Fincham, A. A., 1984. Basic Marine Biology, Cambridge University Press, 

London. 

Gupta, Sen R., Sankaranarayanan V. N., De Sousa S. N., Fondekar, S. P., 1976a. 

Chemical Oceanography of the Arabian Sea: Part 111- Studies on nutrient fraction 

and Stoichiometric relationships in the northern and eastern basins. Indian J. Mar. 

Sci. 5, 58-71. 

Gupa, Sen R., Rajagopal, M. D., Qasim, S. Z., 1976b. Relationships between 

dissolved oxygen and nutrients in the north-westtern Indian Ocean. Indian J. Mar. 

Sci. 5, 201-211. 

Gupta, Sen R., Analia Braganca, Noronha, R. J., Singbal, S. Y. S., 1980. Indian J. 

Mar. Sci. 9, 240-245. 

Ivanenkov, V. N., Rozanov, A. G., 1961. Hydrogen sulphide contamination of the 

intennediate water layers of the Arabian Sea and the Bay of Bengal. Okeanologiia 

1,443-449 (in Russian). 

Joydas, T.V., 2002. Macrobenthos of the shelf waters of the west coast of India. 


Kumar, Hareesh, P. V., Basil Mathew, 1997. Salinity distribution in the Arabian 

Sea. Indian J. Mar. Sci. 26, 271-277. 

Kumar, Prasanna, S., Prasad, T. G., 1996. Winter cooling in the northern Arabian 

Sea. Curr. Sci. 71 (11), 834-841. 

Levinton S. Jeffrey, 1982. In: Marine Ecology. Prentice-Hall Inc., Englewood 

Cliffs, New Jersey. 

46

Naqvi, S. W. A., Noronha, R. J., Reddy C.V.G., 1982. Denitrification in the 

Arabian Sea. Deep Sea Res., 29, 459-469. 

Nejman, V. G., 1961. F onnation of oxygen minimum in the subsurface waters of 

the Arabian Sea. Okeanologicheskie lssledovaniya, 4, 62-65. 

Pankajashan, T., Ramaraju, D. V., 1987. Intrusion of Bay of Bengal water into 

Arabian Sea along the west coast of India during northeast monsoon. Contribution 

in Marine Sciences (Dr. S. Z. Qasim's 60 th birthday Felicitation volume), 237- 

244. 

Qasim, S. Z., 1977. Biological productivity of the Indian Ocean. Indian J. Mar. 

Sci.6, 122-137. 

Qasim, S. Z., 1982. Oceanography of the northern Arabian Sea. Deep Sea Res. 

29, 1041-1068. 

Rao, D. P., Jayaraman, R., 1970. On the occurrence of oxygen maxima and 

minima in the upper 500 meters of the northwestern Indian Ocean. Proceedings of 

the Indian Academy of Sciences. Vot. LXXI, No. 6, Sec. B. 

Sankaranarayanan, V. N., 1978. Some physical and chemical studies of the waters 

of the northern Arabian Sea. Ph.D. Thesis, Kerala University, India. 

Wyrtki, K., 1971. Oceanographic atlas of the International Indian Ocean 

Expedition. National Science Foundation, U.S. Government of Printing Office, 

Washinton D. C. 531 pp. 

Wyrtki, K., 1973. Physical Oceanography of the India Ocean. In: The biology of 

the Indian Ocean. Zeitzschel, B. (Ed) Springer-Verlag. 18-36. 

47

Depths Temperature Salinity Dissolved 

oxygen 

30m 2.3079 (8) 0.7482 (8) 25.5504 (8) 

SOm 7.0498 (7) 0 18.0304 (7) 

7Sm 7.0475 (8) 1.1142 (8) 10.9873 (8) 

lOOm 9.6623 (8) 1.8541 (8) 4.82820 (8) 

lS0m 4.8320 (6) 0.3487 (6) 3.09490 (6) 

Table 1 - Seasonal comparison of environmental parameters based on 

Student's t test (Degree of freedom is given in bracket).

orr Mormugao orr Vernal 

35.36 

35.32 

0 

0 

0 

36.3 

36.2 

0 

35.28 

35.24 

a) 

35.2 

36. 1 

d) 

36 

0 

0 

, , , , , , , , , , , 

20 40 60 80 100 20 40 60 80 100 

35. 16 9 35.9 0 

, 

, 

, 

, - 

35.6 

35.56 

orr Ralnagiri 

0 

0 

36.4 

36.2 

(fJ 

D- 

35.52 

b) 

35.48 I 

36 

e) 35.8 

Orf Porbandrr 

0 

=> 0 0 

£ 

, , , , 1 

35.44 0 

.!: 

0 35.6 0 

n; 35 .4 

0 

35 .4 

(fJ 

" 

0 40 80 120 160 0 40 80 120 160 

35.68 

, , , , 

orr MumbHi Ofr Dwaraka 

0 

36.8 

35.64 0 36.6 

c) 35.6 f) 36.4 

35.56 

35.52 , I 

0 

I 

0 

, I 

36.2 

36 , I , I , I , , , , 

20 40 60 80 100 100 110 120 130 140 150 

---Depths-- 

Fig. 4 - Depth wise distribution of salinity (psu) during post monsoon 

0 

51

4.1. Sediment texture 

4.1.1. Introduction 

4.1.2. Results 

4.1.2.1. Post-monsoon 

4.1.2.2. Pre-monsoon 

4.1.2.3. Seasonal comparison 

4.1.3. Discussion 


4.2. I. Introduction 

4.2.2. Re.wlts 


4.2.2.2. Pre-mon!;oon 




4.1. Sediment Texture 


Chapter 4. 

Sediment characteristics 

The composition of sediment is of vital importance to the benthic biota of any 

aquatic environment. Sediment provides the substratum for organisms to live and 

aslo to obtain food in the form of organic matter. The supply and source of these 

materials and sites of deposition depend upon the various physical and chemical 

environmental factors. The nature and rate of sediment deposited affects the density 

and type of benthic biota in the area. Increase in sediments or sedimentation 

resulting from coastal structure and various river discharges may drastically alter the 

number and type of species dwelling in the region. Sediment characteristics such as 

texture and availability of organic matter are the dominant factors controlling the 

distribution of benthos. 

56

The continental shelf and its adjoining land of the study area is bordered by 

Western Ghats and is influenced by monsoon. The climate is tropical with maximum 

precipitation during monsoon and the shelf is floored with different types of 

sediments. According to Stewert and Pilkey (1965) the continental shelf in the study 

area can be divided into inner shelf and outer shelf marked by the difference in the 

topography and sediment type. Studics by Nair (1971) and Siddiquie and 

Rajamanickam (1974) have shown that the inner shelf has smooth featureless 

topography whereas the outer shelfis fonned by rugged topography. 

Width of the continental shelf varies from about 100 km off Suarashtra (Off 

Dwaraka) coast (Gupta, 1979) to 280 -300 km wide off Mumbai (Kidwai and Nair, 

1972) and this narrows down to about 100 km off Ratnagiri to a progressive 

narrowing of 60 km wide shelf off Monnugao (Nair,1975). The shelf off Mumbai is 

composed of various features like pinnacles with and without adjacent troughs, which 

are usually 1-2 m deep (Nair,1975). In addition to these features a number of large 

mound shaped protuberances with a relief of 6 to 8m are also present. In Ratnagiri 

the pinnacles and troughs are poorly developed as compared to off Mumbai and 

when it reaches Monnugao pinnacles with relatively gentle depression occur on a 

slopping shelf. A notable feature is that pinnacles and troughs are most prominent off 

Mumbai where the shelf is flat and widest and become relatively subdued in profile 

towards south where the shelf is generally half or less than half of width. Wider shelf 

OfT Mumbai narrows in Ratnagiri and further narrows southwards. 

Many workers have studied the substrata of northwestern region and most of 

them pertain to the regional studies including estuaries and gulf regions and a few 

studies were carried out in the shelf region to assess the textural characteristics. 

Kidwai and Nair (1972) studied the sediment texture and distribution of organic 

matter in the NW coast of India (18-22° N) and later, Nair (1975) described the 

nature and origin of small-scale topographic prominences on the western continental 

shelf of India. Parulekar et al., (1976) studied the sediment texture and organic matter 

57

distribution off Mumbai region upto 60 m depths. Ansari et al., (1977) Ansari (1978), 

Hashimi et al., (1978) and Nair et al., (1978) reported the textural characteristics of 

central west coast (13-16° N) of India. Benthos and sediment characteristics of entire 

west coast of India were studied by was that of Harkantra et al., (1980) describing the 

texture and organic matter up to 70 m depth. The other reports were that of Ansari et 

al., (1980) for Monnugao coast (20-840m) and Setty and Nigam (1982) for west 

coast (14-22° N). Vizakat et al., (1991) while studying the population ecology and 

community structure of benthos described the texture and organic matter in the 5-15 

m contour off Konkan, west coast of India and Rao (1991) studied the clay mineral 

distribution in the continental shelf and slope of Saurashtra coast. The other works in 

the west coast included that of Narayana and Prabhu (1993) who studied the texture 

and gcochcmistry of sediments of 110navar shelf, Ilarkantra and Parulckar (1994) 

who studied the benthos and sediment characteristics in the 5-10 m depths of Rajapur 

Bay, west coast of India (16 0 34' N) and Ingole et al., (2002) worked in the coastal 

waters of Dabhol, west coast of India. Joydas (2002) gave an account on the sediment 

texture and macrobenthos of west coast of India. 

4.1.2. Results 

Spatial variations in the sediment characteristics of the northwest continental 

shelf of India are examined in this chapter. Results are described in 3 parts-first part 

deals with sediment texture and its spatial variations during post-monsoon and 

second part deals with the same during pre-monsoon seasons, and seasonal changes 

are described in the third part. 


Six types of texture were observed which include sandy, silty sand, clayey 

sand, silty clay, clayey and mixed type (where sand, silt and clay in almost equal 

proportion) (Fig. 9 a & b). Of these silty clay dominated in the study area. Clayey 

sediment, the second dominant texture, was present at 5 stations followed by sandy 

58

sediments (4 stations). Silty sand was present in 2 stations and clayey sand and 

mixed type texture were present only in onc station each. Spatial distribution showed 

that, generally northern transeets (ofT Porbandar and ofT Dwaraka) showed 

predominance of fine sediment. Shallow depths (30 m and 50 m) of southern 

transeets (offMonnugao, Ratnagiri and Mumbai) and northern transect (ofTVeraval) 

showed more fine sediment texture while beyond 50 m of these transects sand 

fraction increased. 

Distribution of sediment texture in difTerent depth zones is given in Fig. 10. 

Sand percentage increased as depth increased except at > 150 m zone where sand and 

clay were more or less same. Silt was in a medium concentration at all depth zones 

while clay was more in the shallow depth zones (30 and 50 m) and decreased towards 

deeper zone except at > 150 m zone. 

Transect wise variation of sediment texture at each depth zone is given in 

Figs. 11-15. At 30 m zone there was no significant transect wise variation in the 

sediment texture. Sand was low in this zone. Silt fluctuated with highest value ofT 

Mormugao and lowest off Porbandar. Clay was high and no significant variation 

among different stations was observed. At 50 m zone also, sand was generally low 

with slightly higher value recorded ofT Mumbai region. Silt fluctuated with highest 

value off Monnugao and lowest ofT Mumbai. Clay was generally high at all stations 

with minimum value ofT Monnugao and maximum off Porbandar. At 75 m zone, 

sand dominated over clay and increased towards Mumbai and decreased towards 

north and the lowest value observed off Porbandar. Silt percentage was low at all 

transects and fluctuated with maximum value ofT Ratnagiri and minimum ofT 

Veraval. Clay percentage was highly fluctuating with highest value off Porbandar 

and lowest ofT Mumbai region. At 100 m zone, sand percentage increased towards 

north except off Dwaraka, with highest value observed off Veraval and lowest ofT 

Dwaraka. Silt showed the reverse trend and decreased up to ofT Veraval, but the 

highest percentage was observed off Dwaraka. Clay was generally low at all 

59

in deeper depths no change has taken place. Off Veraval region silty clay at 30 and 

50 m was replaced by clayey silt and clayey sand at 75 m also changed to clayey silt. 

Sand in the deeper station showed no change as that of previous transect. Off 

Dwaraka, shallow depth recorded no change in the texture, but in deeper station silty 

clay has changed to sandy clay. In general shallow stations have high clay 

percentage and deeper stations sustained more of sand during both the seasons. Sand 

percentage decreased to north during both seasons however, during post-monsoon 

season the decrease was not as gradual as pre-monsoon. 

Statistical analysis based on Student's t test showed that significant difference 

between two seasons observed in the shallow depths of 30 m and 50 m only (Table 

2). Silt and clay showed significant difference in the 30 m while only clay showed 

considerable di fterence between two seasons at 50 m zone. 


The results of the study revealed transect wise and depth wise variations in the 

texture during the two seasons. Southern part sustained coarser fraction whereas 

northern part showed fine texture. Depth wise, shallow areas sustained more clay 

content and deeper stations had more sand content. Six types of sediment textures 

were obtained during both the seasons, in which silty clay dominated during post 

monsoon while silty clay, clayey sand and sandy sediment were predominant during 

pre-monsoon. 

Occurence of fine sediment texture in the shallow areas and coarser sediment 

in the deeper depths is comparable to that of earlier reports. Nair and Pylee (1968) 

showed that inner shelf (40m) of west coast of India are floored with poorly sorted 

silty clay and further southwards a zone of fine to medium sand exist. Kidwai and 

Nair (1972) pointed out that outer shelf of Mumbai is generally coarser and inner 

shelf is finer with silt and clay. Nair (1975) while elucidating the textural 

characteristics of western continental shelf (off Mumbai to Karwar) of India, reported 

62

fine sediments with comparatively high organic matter (1.9-3.9%) in the inner shelf 

«50m) and sand in the outer shelf (55-90m). Parulekar et al., (1976) reported almost 

a uniform pattern in sediment distribution off Mumbai region upto 60m depths. Mud 

constituted the major component with varying fractions of silt and clay. Beyond 60 m 

depth zone texture showed variations in composition. Hashimi et al., (1978) studied 

the grain size off Vengurla and Mangalore and reported fine sediment (clayey silt and 

silty clay) in the inner shelf and coarser fractions (silty, clayey sand to sand) in the 

outer shelf. Nair et al., (1978) in the same area reported three most abundant 

sediment types which are clayey silt, silty sand and sand. Clayey silt was confined to 

the shallow areas of

deposition of sediments from different sources have worked out by several authors. 

Nair et al., (1978) opined that during the coarse of their transportation from coast, 

some of the fine sediments were deposited on the inner shelf and balance bypassed 

the outer shelf and got deposited. When salinity reduced during monsoon season, low 

saline sediment laden water is discharged into the relatively higher saline waters of 

the inner shelf and thus sediments got tlocculated and deposited. Drake (1976) 

studied the marine sediment transport of southern California and reported that 80% of 

the sediment discharged during tlood was in shallow waters of

Narayana, 1991 ). Limited input of coarser material in the north may be due to 

trapping of coarser material by rivers. During the filtering processes rivers/estuaries 

trap coarse size particle and allow only fine particle to escape into the inner shelf. 

The sandy nature in the outer shelf may be due to the relict nature of sediments and 

the absence of conditions favorable for deposition (Hashimi and Nair, 1981). 

The increased percentage of clay in the northern regions in both seasons may 

be due to the influence of the river Indus in the north. However, clay content in the 

shallow areas of Mormugao area due to the discharge brought by Mandovi and Zuari 

Rivers. Harkantra et al., (1980) described 7 major types of substrata with two 

differentiated areas as north and south of Mormugao (15° N). Sediment was fine and 

dominated by silt and clay in the region north of Mormugao and sandy with little 

percentage of silt and clay in the region south of Mormugao. In the present study also 

study area could be divided into two parts as fine sediment dominated in the north 

and sand dominated in south. Setty and Nigam (1982) found that the inner part of 

Gulf of Kutch area hold very fine-grained clayey silt whereas Mumbai region (16-17° 

N) was sandy in nature below which sediment was mostly clayey with patches of 

sand and silty clay. In Mormugao sector, sandy sediment predominated followed by 

clay. The present data agrees well with the above findings. 

Seasonal variations in the sediment texture could be due to the monsoonal 

flow and also due to the intensity, direction and current speed that makes the 

difference in sedimentation. 

4.2. Organic matter (OM) 


Organic content of bottom sediment may be more causal factor than the 

sediment grain size in determining infaunal distribution because it is a dominant 

source of food for deposit feeders and indirectly for suspension feeders. Organic 

matter (hereafter reffered to as OM) may influence benthos through availability of 

65

food supply and the consumption of OM-bound sediment and subsequent generation 

of faecal pellets, which will alter the mechanical composition of sediments. Bader 

(1954) suggested that size of the sediment particle influence the OM content. 

Extremely small size sediment had large amount of OM and vice versa. In addition to 

the influence through food, OM also influences benthos by regulating the oxygen 

availability in the bottom water and the interstitial space. Bacteria utilize the oxygen 

for decomposition of OM, which in turn reduces the available oxygen to organisms. 

In the decomposition of OM, Bader (1954) opined that in areas where high degree of 

decomposition in a low organic content sediment, the relative amount of 

decomposition per unit volume of sediment will be low when compared with an area 

where the degree of decomposition is same but OM is greater. So, in other words 

coefficient of the degree of decomposition is dependent only upon the actual 

decomposition while the coefficient for the amount of decomposition is dependent 

also upon the amount of organic carbon. Waksman and Starkey (193 I) have shown 

that natural decomposition of OM can produce aldehydes, H2S, methane and many 

other toxic products. Reuszer (1933) and Waksman et al., (1933) have shown that 

degree of decomposition is correlated with the abundance of bacteria. Liagina and 

Kuznetzow (1937), ZoBell and Stadler (1940), ZoBell and Feltham (1942) have 

shown that abundant bacterial activity causes a serious drain on the available oxygen 

supply. So decomposition of OM by bacteria is an ecological factor resulting from 

the production of toxic products and depletion of available oxygen. The factors that 

favour a high organic carbon content in the bottom sediments are: I) abundant supply 

of OM in the overlying waters 2) relatively rapid accumulation of fine-grained 

sediments and 3) low oxygen content of the bottom. According to Parulekar et al., 

(1982,1992) varied but rich benthic fauna and high biomass values are dependent on 

high organic production in the overlying water column. They added that food 

availability is the major factor controlling the distribution pattern of deep-sea 

benthos. Detritus and bacteria fonn the main food for deep-sea benthos (Tietjen, 

66

In general. two ditlerent patterns were observed in the latitudinal distribution 

of OM. In the shallow zones of 30 m and 50 m. OM decreased to north where as in 

the deeper depth zone (beyond 75 m) no regular pattern was observed; however 

northern latitude stations recorded relatively high OM. 


Average of OM in different depth zones is given in Fig. 24. OM was more in 

the shallow depths (30 and 50 m) decreased to deeper depths (100 m), but again 

increased beyond 150 m zone. Transect wise variation at each depth zone is given in 

Table 3. At 30 m depth zone. minimum value was observed off Dwaraka (1.07%) 

and maximum off Ratnagiri (3.63%). At 50 m zone. OM was highly variable and the 

highest value was observed off Ratnagiri and lowest values were noticed off 

Mormugao and Veraval. At 75 m zone also OM fluctuated between stations and 

maximum value was observed off Ratnagiri (1.67%) and minimum off Mormugao 

(0.36%). At 100 m zone high values were found off Mormugao and Ratnagiri and 

low values off Mumbai and Veraval and again an increase was observed off 

Dwaraka. At 150 m depth zone. only 3 observations were made and the OM was low 

otT Mumbai and high off Veraval. At > 150 m depth only one station was sampled 

and high OM (3.33%) was noticed. 

In general. different depth zones recorded different pattern of distribution and 

no particular trend was observed in OM distribution. However. high values were 

found in the southern transect especially 00' Ratnagiri. 


Distribution of OM during the two seasons showed that 65% of the stations 

were influenced by seasonal changes. In the study area most of the stations showed 

significant variation (>60% variation). Majority of the stations showed an increase in 

OM % from post-monsoon to pre-monsoon. Maximum variation was found at 100 

m depth ofT Mormugao (0.48% of OM during post-monsoon changed to 1.78% 

68

during pre-monsoon) followed by 75 m depth off Porbandar (0.36% of OM changed 

to 1.31 %). The lowest variation was found at 120m off Mumbai. Likewise in other 

transects significant variation:; were observed which could be attributed to the 

seasonal changes. Student's t test showed that significant difference was observed 

only in the 30 m depth and eventhough variations in deeper depths notivced but were 

not at a significant level. 


OM showed considerable variation with respect to depth and latitude. In 

general more OM was retained in the fine sediments in the shallow zones (30 and 50 

m). The minimum average values were found at 75 and 100 m depths «I %) and 

maximum average values were found at 30 and 50 m depths (1.5-2%) during both 

seasons. 

In general, OM in the sediment was related to the texture of the sediment. In 

the present study OM ranged from 0.36 to 3.33% during post-monsoon and from 0.18 

to 4.52 % during pre-monsoon season. Low values were found in sandy or sand 

dominating sediment and high values were found in the finer sediments during both 

seasons. Affinity of OM towards fine sediment fraction has observed by several 

workers. Murthy et al., (1969) reported OM off Mumbai ranging from 0.24 to 3.15% 

(av. 1.93%) in the silt-clay fractions. Kidwai and Nair (1972) reported an OM in the 

clay and silt ranging between 4 and 8 % in the NW coast of India. Parulekar et al., 

(1976) studied the OM off Mumbai region and suggested that clay and silty clay 

retained higher OM than the sand and clayey sand substratum. Hashimi et al., (1978) 

reported the OM up to 5% in the fine grained sediment of the inner shelf and

et al., (1980) reported values in the range of 0.62 to 2.05% off Goa region with 

highest value in the outer most station, which was muddy in nature while Harkantra 

et al., (1980) reported OM varying from 0.47 to 6.18% (av. 3.15%) in the west coast 

ofIndia. Higher organic carbon in the fine substrata of clay and silt and low values in 

the sandy substratum also suggested a relationship with the textural characteristics of 

the sediment. Narayana and Prabhu (1993) recorded the OM ranging between 0.1 and 

2.87% with uneven distribution in the Honavar shelf, west coast of India. Joydas 

(2002) reported a value ranging from 0.24-6.23% with an average of 2.81 which is 

slightly higher than the present study. 

One factor favouring the accumulation and preservation of OM in mud was 

the sediment size. The fine-grained sediments have larger surface area and tend to 

adsorb more OM than coarse sediments. This may be the reason for high OM in the 

fine-grained sediment. Once associated with mud, OM remains preserved due to high 

rate of sedimentation in the near shore region and the reduced condition associated 

with such rapidly deposited mud. This preservation together with new discharge from 

rivers increases the OM in the inner shelf region. 

Present study showed high OM in shallow and deeper regions and a low OM 

in between. During pre-monsoon and post-monsoon seasons, OM was high in the 

shallow zones (30 and 50 m). The high OM in the shallow regions may be due to 

river discharge and high biological productivity in the overlying water (Degens and 

Ittekott, 1984) and may also be due to the impact of low energy conditions prevailing 

in the area that accumulate fine sediments which can hold more OM (Hashim et al., 

1978). During the coarse of their transportation from the coast, some of the fine 

sediment gets deposited on the inner shelf and balance bypasses to the outer shelf and 

gets deposited (Nair et al., 1978). The reason for high OM at 50 m depth especially 

during post-monsoon, in the present study may also be due to the bypassing of the 

fine sediment in the shallowest region and getting deposited a little away from the 

coast. 

70

Present study also showed high OM in stations beyond 100 m depth during 

both seasons. Increased OM in the outer regions of Monnugao and off Veraval may 

be due to the low oxygen content (Carruthers et al., 1959) in these areas preventing 

degradation, especially off Veraval where the DO was low «0.5ml/l). Nair (1975) 

also reported inner shelf with high OM (1.9-3.9%) against the outer region (0.88- 

0.95%) from the western continental shelf(14-18° N) of India and also attributed this 

high OM to the reducing environment in the sediment. Joydas (2002) also reported 

similar results of high OM in the shallow and deeper depths and low values in the 76- 

100 m zone. It was suggested that high concentration of organic carbon in the deep 

sediment layer could be due to the presence of refractory fraction of OM left after the 

carbon mineralisation (Anon, 1997). High OM in deeper depths may also be a result 

of the preservation under a reducing environment and in part by the rapid deposition 

(Kidwai and Nair, 1972). The high OM in the shallow and deeper areas may be 

attributed to the fine-grained nature of the sediments and to the variation in the 

benthic productivity (Paropkari et al., 1978). They also have attributed that the grain 

size and biological productivity are the major contributing factors for the variation in 

OM content in the area. Kolla et al .. (1978) opined that the factors such as biological 

productivity, water depth, pressure, turbulance and water chemistry influence the OM 

distribution. 

An additional feature relevant to the distribution of OM in marine sediments is 

the difference in composition of OM. If the OM is proteinaceous in nature it is 

hydroJyzed during diagenesis (cementation and re-crystallization) and if it contains 

humic acid and lignitic OM, it survives compaction and diagenesis (Degens et al., 

(1969). Kidwai and Nair, (1972) suggested that the distribution of OM in a 

depositional environment might be explained in tenns of its production, destruction 

and dilution in the environment. A marine depositional environment contains usually 

allochthonous OM transported to the site of deposition by river discharge and 

autochthonous OM, which originates at the site of deposition by the degradation of 

71

organisms living in the water and the bottom. Rate of production of OM are usually 

higher in areas of upwelling. 

Latitudinally, OM decreased to north below 75 m and beyond 75 m, 

fluctuating values were observed with exceptional high values in the north during 

post-monsoon. During pre-monsoon, no regular trend was observed, but relatively 

high values were found in southern transects especially off Ratnagiri. But Joydas 

(2002) could not observe any latitudinal trend in OM distribution in the west coast. 

The seasonal difference in the distribution of OM can be attributed to the 

changes in the texture of the sediment. The amount of riverine input, filtration 

activities of the rivers and estuaries, strength of the waves and currents, amount of 

DO in the bottom water together with degradation by microorganisms may be 

playing a role in the variations in the OM distribution. 

72


Anon, 1997. Benthic disturbance and impact studies-phase 11 of environment impact 

assessment for nodule mining index. Technical report, NIO, Goa, India. 

Ansari, Z. A., 1978. Meiobenthos from the Karwar region (Central West Coast of 

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meiobenthos off Goa coast, India. Hydrobiologia 74, 209-214. 

Ansari, Z. A., Parulekar, A. H., Harkantra, S. N., Ayyappan Nair, 1977. Shallow 

water macrobenthos along the central west coast of India. Mahasagar 10 (3&4), 123- 

127. 

Bader R. G., 1954. The role of organic matter in determining the distribution of 

pelecypods in marine sediments. J. mar. Res. 13,32. 

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183,1084. 

Degens, E. J., Emery K.O., Reuter, J .H., 1969. News. Jahrl. Geol. Paleontol. Monatsh 

231. 

Degens, E. J., Ittekkot, V., 1984. In Nord-Sud Profile: Zentraleuropa 

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Stanley, DJ., Swift, D. J. P. (Eds.)(John Wiley & Sons, New York, 127 pp. 

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Harkantra, S. N., Ayyappan Nair, Ansari, Z. A., Parulekar, A. H., 1980. Benthos of 

the shelf along the west coast of India. Indian J. Mar. Sci. 9, 106-110. 

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of Raj pur bay, central west coast of India. Indian J. Mar. Sci. 23, 31-34. 

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Hashimi, N. H., Kidwai, R. M., Nair, R. R.,1978. Grain size and coarse-fraction 

studies of sediments between Vengurla and Mangalore on the western continental 

shelf ofIndia. Indian J. Mar. Sci. 7, 231-238. 

Ingole Baban, Nimi Rodrigues, Zaker Ali Ansari , 2002. Macrobenthic communities 

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Ph.D. Thesis, Cochin University of Science and Technology 

Kidwai, R. M., Nair, R. R., 1972. Distribution of organic matter on the continental 

shelf of Bombay: A terrigenous- carbonate depositional environment. Indian J. Mar. 

Sci. 1(2), 116-118. 

Kolla, V., Be, A. W. H., Biscaye, P. E., 1978. Calcium carbonate distribution in the 

surface sediments of the Indian Ocean. J Geophys. Res. (Oceans and Atmosphere) 

81,2605-2616. 

Krone, R., 1962. Flume studies of the transport of sediment in estuarial shoaling 

processes, final report, hydraulic Eng.Lab. and sanitary Eng.Res. Lab. (University of 

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Kuenen, PH.H., 1965. In: Submarine geology and geophysics, edited by W.F. 

Whittard and R. Bradshaw (Colston Research Society, Butterworths, London),47 pp. 

Liagina, N. M., Kuznetzow, S. I., 1937. The detennination of the intensity of 

respiration of some species of water bacteria at various temperatures under laboratory 

conditions (in Russian, with English summary). Mikrobiologia, 6, 21-27. 

Mann, K. H., 1982. Ecology of coastal waters: A system approach. (University of 

California press, Los Angeles) 256 pp. 

Mc Cave, I. N., 1972. In: Shelf sediment transport process and pattern. Swift, D. J. 

P., Duane, D. B. and Pilkey, O. H. (Ed.) (Dowden Hutchinson and Ross, 

Inc.Stroudsburg), 225 pp. 

Murthy P. S. N., Reddy C. V. G., Varadachari, V. V. R., 1969. Proc. Nat. Inst. Sci. 

India 35 b, 167. 

Nair R. R., Pylee, A. 1968. Size distribution and carbonate content of the sediments 

of the western continental shelf of India. Bull.natLinst.sci. India.38, 411-420. 

74

Nair, R. R., Hashimi, N. H., Kidwai, R. M., Gupta, M. V. S., Paropkari, A. L., 

Ambra, N. V., Muralinath, A. S., Mascarenhas, A., D'costa, G. P., 1978. Topography 

and sediments of the western continental shelf of India - Vengurla to Mangalore. 


Nair, R R., 1971. Beach rock and associated carbonate sediments of the fifty fathom 

flat, a submarine terrace on the outer continental shelf off Bombay. Proc.lndian 

Acad.Sci. 72(3), 148-154. 

Nair, R R, 1975. Nature and origin of small-scale topographic prominences on the 

western continental shelfofIndia. Indian J. Mar. Sci. 4, 25-29. 

Narayana, A. C., Prabhu, Venkatesh 1993. Textural and geochemical studies of relict 

and modern sediments of the continental shelf off Honavar, West Coast of India. 

Journal Geological Society ofIndia 41,299-305. 

Nayak, G. N., 1996. Grain size parameters as indicator of sediment movement 

around a river mouth, near Karwar, west coast of India. Indian J. Mar. Sci. 25, 346- 

348. 

Pandarinath, K., Narayana, A. C., 1991. Textural and physico-chemical studies of 

inner shelf sediments off Gangoli, west coast of India. Indian J. Mar. Sci. 20, 118- 

122. 

Paropkari, A. L., 1979. Distribution of organic carbon in sediments of the 

northwestern continental shelfofIndia. Indian J. Mar. Sci. 8,127-129. 

Paropkari, A. L., Rao, Ch. M., Murty, P. S. N., 1978. Geochemical studies on the 

shelf sediments off Bombay. Indian J. Mar. Sci. 7, 8-11. 

Parulekar, A. H., Harkantra, S. N., Ansari, Z. A., Matondkar, S. G. P., 1982. Abyssal 

benthos of the central Indian Ocean. Deep Sea Res. 29,1531-1537. 

Parulekar, A. H., Nair, S. A., Harkantra, S. N., Ansari Z. A., 1976. Some quantitative 

studies on the benthos off Bombay. Mahasagar 9 (1&2),51-56. 

Parulekar, A. H., Ingole, B. S., Harkantra, S. N., Ansari, Z. A.,1992. Deep-sea 

benthos of the western and central Indian Ocean. In: Oceanography of the Indian 

Ocean, B.N. Desai (Ed.) Oxford-IBH pub. Co., New Delhi, 261-270 pp. 

75

Postma, H., 1967. In Estuaries, LaufTG. H. (Ed.) (Am. Assoc. Adv. Sci., Washington 

DC) 158 pp. 

Prabhu Venkatesh, H., Hariharan, V., Katti, R. J., 1997. Textural characteristics of 

near shore sediments of Honnavar, southwest coast of India. Indian J. Mar. Sci. 26, 

392-394. 

Rao, Purnachandra V., 1991. Clay mineral distribution in the continental shel f and 

slope offSaurashtra, West Coast off India. Indian J. Mar. Sci. 20,1-6. 

Reuszer, H. W., 1933. Marine bacteria and their role in the cycle oflife in the sea. Ill. 

The bacteria in the ocean waters and mud about Cape Cod. BioI. Bull. Woods Hole. 

65,48-97. 

Setty, Anantha Padmanabha M.G., Nigam Rajiv, 1982. Foraminiferal assemblages 

and organic carbon relationship in benthic marine ecosystem of western Indian 

continental shelf Indian J. Mar. Sci. 11,225-232. 

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continental margin of India. Initial report and data file of INS Darshak 

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Oceanography, Ref No. 74-1,228-233. 

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Geo!., 3, 411-427. 

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Carolina. Deep Sea Res. 18, 941-957. 

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community structure of subtidal soft sediment dwelling macro-invertebrates of 

Konkan, West coast ofIndia. Indian J. Mar. Sci. 20 (1),40-42. 

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Waksman, S. A., Starkey, R. L., 1931. In: Soil and microbe. John WiJey & sons, Inc. 

New York 260 pp. 

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76

ZoBell, C. E., Stadler, J., 1940. The oxidation of lignin by lake bacteria. Arch. 

Hydrobiol. Plankt. 37, 163-171. 

77

Depths Sand Silt Clay Organic 

matter 

30m 0.1835 8) 4.0213 (8) 4.0450 (8) 2.2024 (8) 

SOm 0.5039 (7) 1.3402 (7) 3.0123 (7) 0.4776 (7) 

7Sm 0.6190 (8) 0.0718 (8) 0.8414 (8) 0.6344 (8) 

100 m 0.7095 (8) 0.0323 (8) 1.0083 (8) 0.2217 (8) 

lS0m 1.1455 (6) 2.2272 (6) 0.5924 (6) 0.3007 (6) 

Table 4 - Seasonal comparison of sediment characteristics based on 

Student's I test (Degree of freedom is given in bracket) 

80

100 

80 

'" 60 

• 40 

2 • G R M V 

Transects 

G· Off Monnugao, R- Off Ratnagiri. M- Off Mumbai, 

V- OtrVeraval, P- OITPorbandar 

p 

• clay 

Dsill 

Dsand I 

Fig. 12 - Transect wise di stribution of sediment texture at 50 m 

• '" 

100 

80 

60 

40 

2 • G R M V 

Transects 

G-Off Monnugao, R- OfT Ratnagiri. M- OfT Mumbai. 

v - OffVeraval. p- Off Porbandar 

p 

. clay 

O silt 

D sand 

Fig. 13 - Transect wise distribution of sediment texture at 75 m 

83

• 

PRE'MONSOON 

SOUTHERN'TRANSECTS 

Fig. 16a. Triangular diagram showing sediment distribution in 

southern transects during pre-monsoon season 

• 

PRE - MONSOON 

NORTHERN TRANSECTS 

----'''----- -----L-------''----S-IL-'T 

Fig. 16 b Triangular diagram showing sediment distribution in northern 

transects during pre-monsoon season 

85

5.1. Introduction 

5.2. Results 

5.2.1. Biomass of macro be nth os 

5.2. J. 1. Post-monsoon 


5.2.2. Density of macro be nth os 



5.2.3. Biomass ofmeiobenthos 

5.2.3.1. Posl-monsoon 


5.2.4. Density ofmeiobenthos 

5.2.4. I. Post-monsoon 



5.3. Di!i'cussion 



Chapter 5. 

Standing Stock 

It is well recognized that benthic production is a tool for measurmg the 

hiological productivity of an area. Estimation of standing stock of henthos is 

important for the assessment of demersal fishery resources, as they form an important 

source of food for demersal fishes and shellfishes. Benthic organisms have an 

important role in the food chain, either at secondary level as feeding detritus and 

plant material or at tertiary level as food for predators. Hence, the availability of 

benthos at any region can be an indicator of demersal fishery potential of that area. 

The standing crop of macrobenthos is not only important to the demersal fishes 

which directly feed on them, but also to many pelagic species that restrict to shallow 

waters during some period of their life. Also, benthic organisms have been regarded 

'lO

as the best indicators of the environmental changes caused by pollution, because of 

their constant presence, relatively long life span, sluggish or sedentary habits and 

tolerance to differing stress. 

Quantitative study of benthos attained importance after the work of Peterson 

(l911, 1913) in Danish waters. Belegvad (1930,1932), Jones (1956) and Sanders 

(1956) after carrying out intensive studies on the bottom fauna have revealed the 

importance of study of benthic biomass in the evaluation in utilization of benthos as 

food for higher carnivores and fishes. Sanders (1969) and Sanders et al., (1965) also 

studied faunal distribution and salinity and ecology of deep-sea benthos. 

In the Indian basin, the bottom fauna was first studied by Annandale (1907) 

and Annandale and Kemp (1915). Neyman (1969) reported the benthos of the 

shelves in the northern part of Indian Ocean and Desai (1973) studied the benthic 

productivity of the Indian Ocean. After that Parulekar (1981), Parulekar et al., (1982 

b) worked on the benthos of the Indian Ocean and other investigations on the benthos 

of the entire Indian basin includes Parulekar et al., (1982a), Parulekar (1985), 

Parulekar et al., (1992) and Ansari et al., (1996). Harkantra et al., (1980) studied 

the benthos of the entire west cost up to 70 m depth, Joydas and Damodaran (2001) 

studied the polychaetes along the west coast of India and Joydas (2002) reported the 

macrobenths along the west coast of India. Most of the studies in the west coast were 

concentrated on the central west coast, which includes the works of Parulekar (1973), 

Ansari et al., (1977b), Harkantra and Parulekar (1981), Devassy et al., (1987), 

Varshney et al., (1988), Vizakat et al., (1991), Prabhu et al., (1993) and 

Gopalakrishnan and Nair (1998). In the southwest coast, the earlier reports on the 

benthos from the coastal and estuarine waters were mainly from the investigations of 

Seshappa (1953), Kurian (1953,1967), Damodaran (1973) and Pillai (1977). The 

works pertaining to NW coast of India were a few, of which Savich (1972) and 

Prabhu & Davan (1974) have demonstrated a direct relation between demersal fish 

catch and abundance of bottom fauna of the Pakistan shelf and Morrnugao coast 

91

espectively. Parulekar and Wagh (1975) and Qasim (1982) also studied the benthos 

of shelf region of NW coast of India. Other works on benthos along the northwest 

coast of India were that of Parulekar et al., (1976) off Mumbai, Harkantra and 

Parulekar (1994) off Rajapur Bay, and Ingole et al., (2002) of Dabhol. 

5.2. Results 

Spatial variations in the benthic biomass and density of the northwest 

continental shelf of India are examined and discussed in this chapte in 5 parts. First 

and second part deals with biomass and density of macrobenthoc during post 

monsoon and pre-monsoon seasons, third and fourth part deals with biomass and 

density of macro be nth os and fifth part deals with the seasonal comparison. 

S.2.1. Biomass of macrobenthos 


Averages of total biomass were given in Fig. 25. Maximum biomass was 

observed at 30 m zone (8.01 g/m 2 ) and minimum at 150 m zone (0.79g/m2). Average 

values showed a decrease towards deeper depths. Transect wise biomass of various 

groups in different depth zones is given in Table 5. At 30 m depth zone, total hiomass 

varied from 3.72 g/m 2 (off Mumbai) to 16.07g/m 2 (off Veraval) with an average of 

K.Olgitn 2 • In most of the stations polychaetes contributed more to the total hiomass 

except ofT Ratnagiri and off Porbandar stations where miscellaneous groups 

collectively contributed more to the total biomass than polychaetes. Contribution of 

miscellaneous group was mainly from sipunculids. At 50 m zone total biomass varied 

from 1.71 glm 2 (offMormugao) to 18.88 g/m 2 (offVeraval) with an average of6.75 

glm 2 • In most of the stations polychaetes contributed more to the total biomass 

except ofT Ratnagiri and Mumbai where molluscs contributed more to the total 

biomass than polychaetes. At 75 m zone total biomass varied from 0.44 g/m 2 (ofT 

Monnugao) to 1.7g/m 2 (off Veraval) with an average of 0.88 glm 2 • In this depth 

')2

showed that northern transects have higher values (4.34 g/m 2 ) than southern transects 

(2.75 glm 2 ) (Fig. 26). 


Average values for total biomass in different depth zones is given in Fig. 25. 

Average of total biomass was maximum at 50 m depth zone (7.46 g/m 2 ) and 

minimum at> 150 m depth zone (0.32 g/m2). Generally high biomass was observed in 

the shallow depths (upto 75 m)and low biomass beyond 75 m depth. Transect wise 

biomass distribution at different depth zones is given in Table 6. At 30 m depth zone, 

total biomass varied from 0.86 g/m 2 (off Ratnagiri) to 14.25 g/m 2 (off Dwaraka) with 

an average of 4.69 g/m 2 . Qualitative composition at this depth zone showed that 

miscellaneous groups collectively contributed more followed by polychaetes to the 

total biomass. Contribution of miscellaneous groups was mainly from stations off 

Dwaraka, Veraval and Monnugao. Off Monnugao sipunculids contributed more and 

otT Veraval and Dwaraka, juvenile fish, sipunculids and nemertene worms 

collectively exceeds the polychaete biomass. At 50 m depth zone, total biomass 

varied from 1.56 g/m 2 (off Ratnagiri) to 15.87 g/m 2 (off Mumbai) with an average of 

7.46 glm 2 . At this zone average value showed that polychaete had a discrete 

dominance over all other groups in contributing more to the total biomass. At 75 m 

zone total biomass varied from 2.6 glm 2 (off Monnugao) to 17.51 glm 2 (off 

Ratnagiri) with an average of 6.85 g/m 2 . Even though average biomass of 

polychaetes was high, contribution of polychaetes were low at stations ofT Monnugao 

and Veraval. Off Monnugao, contribution of molluscs was more to total biomass 

than Polychaetes while offVeraval, crustaceans and miscellaneous group contributed 

more. Molluscs comprising of bivalves and gastropods and miscellaneous group 

constituted mainly by juvenile fishes and nemertene wonns. Crustaceans comprised 

mainly of amphipods. At 100 m zone total biomass varied from 0.87g/m 2 (off 

Mormugao) to 3.95 g/m 2 (off Dwaraka) with an average of 2.07 g/m 2 . Even though 

average biomass of polychaerte was high, its contribution to the total biomass was 

94

more only at stations off Ratnagiri and Dwaraka. Off Monnugao, Mumbai and 

Veraval stations contribution of molluscs was more especially off Veraval. At 1)0 m 

zone, only three observations were made and total biomass varied from 1.76 g/m-' (off 

Veraval) to 5.86 glm 2 (off Mumbai) with an average of 3.43 glm 2 • Even though 

average biomass was maximum for crustaceans, at each station different groups 

contributed more to the total biomass, i.e., polychaetes have higher contribution to 

the total biomass at station off Dwaraka, crustaceans contributed more to the total 

biomass off Mumbai and molluscs showed better contribution to the total biomass otT 

Veraval. At > 150 m depth zone, only two observations were made and total biomass 

varied between 0.02 glm 2 (offVeraval) to 0.61 glm 2 (otT Mumbai) with an average of 

0.32 glm 2 • Off Mumbai, crustaceans and miscellaneous groups exceeded polychaetes 

whereas off Veraval polychaetes alone were present. 

Transect wise variation of total biomass in each depth zone showed a general 

increase to north (Table 6). At 30 m depth zone total biomass exhibited wide 

variation with a general increase towards north. At 50 m zone, total biomass was 

fluctuating transect wise while at 75 m depth zone a general increase to north was 

observed with e {ceptionally high value off Ratnagiri. At 100 m zone also an 

increasing trend was observed in biomass distribution towards north except otT 

Mumbai transect. At 150 m zone, 3 observations were done, total biomass decreased 

from off Mumbai to off Veraval and then increased to Off Dwaraka. In general there 

was a northward increase in biomass. Few exceptional values in the southern stations 

noticed were off Ratnagiri and Mumbai. Southern and northern average values 

showed comparatively high biomass in north (Fig. 27) 

5.2.2. Density of macrobenthos 

5.2.2.1. Post-monSooD 

Averages of total density were given in Fig. 28. Highest total average density 

was recorded at 30 m zone (2654 I m 2 ) and lowest at 150 m zone (257 / m 2 ) and 

95

decreased from shallow to deeper depths. Transect Wlse density distribution in 

different depth zones during post-monsoon is given in Table 7. At 30 m zone total 

density ranged from 360 (off Porbandar) to 48201 m 2 (off Mormugao) with an 

average of 26541 m 2 • Polychaetes dominated at all the stations followed by 

crustaceans. At 50 m zone, total density ranged from 210 I m 2 (off Ratnagiri) to 

41001 m 2 (off Veraval) with an average of 13881 m 2 • In this zone also polychaetes 

showed an obvious dominance over other groups. Crustaceans were the second 

dominant group in most of the stations. At 75 m zone, total density varied from 110 

/ m 2 (ofT Porbandar) to 9421 m 2 (off Ratnagiri) with an average of 4641 m 2 and 

polychaetes had a distinct dominance over other groups. Crustaceans were the second 

dominant group in most of the stations. At 100 m zone, total density ranged from 25 

/ m 2 (ofT Veraval) to 770/m 2 (off Monnugao) with an average of 327 / m 2 • At all the 

stations polychaetes dominated except off Dwaraka where molluscs dominated. At 

150 m zone three stations were sampled and density ranged between 901m 2 (otT 

Ratnagiri) and 560 1m2 (off Dwaraka) with an average of 257 1m 2 . Polychaetes 

dominated off Ratnagiri and Porbandar while molluscs dominated off Dwaraka. 

Transect wise density distribution in different depth zones during post 

monsoon is given in Table 7. Transect wise variation of total density showed that at 

30 m zone there was a gradual decrease in total density towards north except off 

Veraval. At 50 m zone, total density fluctuated with. low value off Ratnagiri and 

high value offVeraval while at 75 m zone, high values were-seen in southern transect 

stations with a decreasing trend towards north. At 100 m zone also decreasing trend 

was noticed in total density towards north with an exceptionally high value off 

Dwaraka mainly because of the presence of molluscs and polychaetes. In 150 m zone 

as an exception from the other depth zones, an increase was observed for total 

density towards north with exceptional high value off Dwaraka. In general 

comparatively high density was observed in southern transect stations in most of the 

depth zones. Average values of southern and northern transects also showed 

96

elaatively higher average density in the southern transect (1200/m2) and lower in the 

northern transect (800/m 2 )(Fig. 29). 


Average of total density in different depth zones is given in Fig. 28. Average 

density was highest at 75 m (3578/m 2 ) and lowest at >150m (620/m 2 ). Density first 

increased from 30 m to 75 m zone then decreased to deeper depths. Transect wise 

density distribution in different depth zones during pre-monsoon is given in Table 8. 

At 30 m zone total density varied from 570/m 2 (off Ratnagiri) to 1740/m 2 (off 

Dwaraka) with an average of 1220/m 2 . At an stations polychaetes dominated in the 

population counts except off Ratnagiri where density of molluscs was more than that 

of polychaetes. At 50 m zone total density varied from 710/m 2 (off Ratnagiri) to 

5250/m 2 (off Mormugao) with an average of 2623/m 2 • At all the stations polychaetes 

had an obvious dominance over all other groups. In the next depth zone, 75 m, total 

density varied from 530/m 2 (offVeraval) to 10090/m 2 (otT Ratnagiri) with an average 

of 3 578/m 2 • As that of previous depth zone, here also polychaete had a wen-defined 

dominance at all stations followed by miscellaneous group and crustaceans. At 100 m 

depth zone total density varied from 1760/m 2 (off Dwaraka) to 2400/m 2 (ofTVeraval) 

with an average of 2060/m 2 and polychaetes dominated at all stations. At 150 m 

zone, total density varied from 140/m 2 (off Veraval) and I 885/m 2 (off Mumbai) with 

an average of 1493 1m 2 • At this zone, off Veraval station, molluscs dominated and 

polychaete density reduced considerably than rest of the groups. At > 150 m zone 

only two stations were sampled and total density ranged between 101m 2 (off 

Veraval) and 1230 1m 2 (off Mumbai) with an average of 620 1m 2 . Off Mumbai, 

polychaete dominated followed by miscellaneous group and crustaceans while off 

Veraval only polychaete was present and lowest density in the study area was 

observed at this station. 

Transect wise density distribution in different depth zones during pre 

monsoon is given in Table 8. Transect wise variation of density distribution in 

97

different depth zones showed that at 3v lJl zone. total density was fluctuating with 

high average values in north. At 50 m also total density fluctuated with low value off 

Ratnagiri and high value off Monnugao station. At 75 m depth zone, fluctuating 

trend was observed and variation of total density between transects was more in this 

zone. Highest value was observed off Ratnagiri and lowest off Veraval. At 100 m 

lone, the variation among transect was low and no regular trend was observed along 

transects. At 150 m zone, fluctuating trend was observed. Off Mumbai and Off 

Dwaraka total density was more or less similar and off Veraval, total density reduced 

significantly. It was comparatively high in southern latitude station (off Mumbai) and 

then decreased to off Veraval then showed an increase to off Dwaraka, thus showing 

an irregular pattern. At > 150 m zone, only two stations were sampled and high total 

density was observed off Mumbai and low off Veraval. In general no regular transect 

wise trend was observed in total density. however, average values showed relatively 

high values in the southern transect (Fig. 30). 

5.2.3. Biomass of meiobenthos 


Biomass distribution of meiobenthos during post-monsoon season is given in 

Table 9. Average biomass showed a general decrease towards deeper depths with 

highest value at 30 m (1.91 mg/IO cm 2 ) and lowest at 150 m (0.08 mg/IO cm 2 ). At 

30 m lone, total biomass varied from 0.66mg/1O cm 2 (Off Monnugao) to 4.09 mg/IO 

cm 2 (off Veraval) with an average of 1.91 mg/IO cm 2 • Contribution of individual 

groups to the total biomass at different depth zones showed that nematodes 

contributed more to the total biomass followed by copepods. Relatively higher values 

were observed in the northern transect stations. At 50 m zone, total biomass variec 

from 0.55 mgllO cm 2 (off Porbandar) to 1.39 mg/lO cm 2 (off Ratnagiri) with an 

average of 0.98 mg/lO cm 2 • Here also nematodes contributed more to the total 

biomass. Off monnugao, low biomass was noticed and off Ratnagiri recorded 

98

that nematodes contributed 27.3 (10 to lill; total biomass, copepods contributed 4.8% 

and rest of the groups collectively contributed 67.8% to the total biomass. 

5.2.4. Density of meiobenthos 


Density distribution of meiobenthos during post-monsoon season is given in 

Table 12. Average of total density showed that density decreased towards deeper 

depths. Highest average density was observed at 30 m (427/10 cm 2 ) followed by 50 

m (187/10 cm 2 ) and lowest at 150 m (l3/10cm\ Nematodes were the dominant 

group contributing 91 % to the total population (Fig. 32). Of the remaining groups, 

copcpods were relatively more (4%) followed by foraminifers and miscellaneous 

groups. 

At 30 m depth zone, density varied from 144110 cm 2 (off Ratnagiri) to 770/10 

cm 2 (ofT Veraval) with an average of 427/10 cm 2 (Table 12). Nematodes were the 

dominant group followed by copepods and ioraminifers. Relatively high density was 

observed in north. At 50 m zone, total density varied from 95110 cm 2 (otIPorbandar) 

to 285/10 cm 2 (off Ratnagiri) with an average of 187110 cm 2 . Here also nematodes 

were the dominant group followed by foraminifers, and copepods contributed least to 

the total density. At this depth, comparatively high density in the southern transects. 

At 75 m zone, total density varied from 41 110 cm 2 (ofTVeravai) to 177 110 cm 2 (ofT 

Mormugao) with an average of 90/10 cm 2 , Nematodes dominated the zone, followed 

by copepods, and foraminifers. Here also southern transects recorded more density. 

At lOO m zone, total density varied from 38/10 cm 2 (off Ratnagiri) to 128110 cm 2 (off 

Mormugao) with an average of 66/10 cm 2 • More or less similar density was obserced 

at all stations except off Mormugao. Similar to the previous depth zone, here also 

nematodes were the dominant taxa, copepods were the second dominant group and 

foraminifers were the least abundant group. At 150 m zone, total density varied 

from 9/10 cm 2 (off Dwaraka) to 19/10 cm 2 (ofT Ratnagiri) with an average of 13/10 

100

cm 2 with a dominance of nematodes. In general no distinct transect wise trend was 

observed. 

Percentage contribution within individual group at different depth (Table 13) 

showed that contribution of nematodes decreased with increasing depth while, rest of 

the groups showed an opposite trend. Highest contribution of nematodes was at 30 m 

(56.7%) and lowest at 150 m (1.5 %). Copepods contributed maximum at 150 m 

zone (37.4%) and minimum at 50 m zone (9%). Miscellaneous groups also have 

relatively lower percentage contribution at 30 m (19.7%) and higher contribution at 

deeper depths of 100 m (28.5%), but exceptionally low value at 150 m (3.6%). 


Density followed the similar trend as that of biomass with relatively low 

density at the 30 m depth off Mormugao and Mumbai while, high density was 

observed at 30 m depth off Ratnagiri, Veraval and Dwaraka (Table 14). Overall 

percentage contribution by various groups to the total density (Table 14) showed that 

nematodes contributed more to the total density (65.3%) followed by foraminifers 

(25%) and miscellaneous groups (8%). Copepods were the least abundant group 

(1.3%). 


In general, average biomass and density of macrobenthos in the whole study 

area were high during pre-monsoon season than post-monsoon period (Fig. 33&34). 

In both seasons shallow depth stations registered high biomass and density, while it 

reduced considerably in deeper stations with some exceptions. During post-monsoon, 

even though no regular trend was observed, average biomass showed comparatively 

high value in the northern transect than its southern counterpart (Fig. 26). Biomass 

showed a northward increase during pre-monsoon. Average value of this season also 

showed comparatively high value in the northern transect than southern transect 

(Fig. 27), however, exceptionally high biomass was observed at 75 m depth otT 

101

Ratnagiri. Density was comparal ively high in the southern transects in both seasons 

(Fig. 29&30). All depth zones of pre-monsoon season recorded high biomass except 

at 30 m depth zone, and at few depth zones the seasonal variation was more. 

During post-monsoon, generally all the groups have high biomass in shallow 

areas (30 m and 50 m) and low at deeper zones (beyond 50 m). in addition to the 

high biomass of crustaceans in the shallow depths, it was also more in the middle or 

deeper depths off Monnugao (lOO m) Ratnagiri (150 m) and Mumbai (75 m). During 

pre-monsoon season polychaetes and miscellaneous groups showed high biomass up 

to 7S m depth and low values beyond 75 m while crustaceans showed low biomass in 

shallow areas (up to 50 m depth) in all transects and high in middle (75 m) or deeper 

depths (beyond 75 m). Molluscs were high in deeper stations (from 75 m to 150 m). 

In other words, season wise comparison showed that during post-monsoon most of 

the groups have more biomass in shallow areas while during pre-monsoon only 

polychaetes and other groups have more biomass in shallow areas (30 m and 50 m). 

Students t statistical analysis (Table 15) showed no significant difference in 

biomass and density between two seasons except for the polychaete density and total 

density at 100 m depth zone. Observed difference may be due to the uneven 

distribution of organisms in various stations. Seasonal comparison for meiobenthos 

was not possible due to lack of sufficient data, however, average biomass and density 

of meiobenthos showed relatively higher values during pre-monsoon than post- 

monsoon. 

53. Discussion 

In the present study biomass in the whole study area varied from 0.05 to 

18.88g/ m 2 (av. 3.81g1 m 2 ) during post-monsoon and 0.02 to 15.87g1m 2 (av. 4.53g/ 

m 2 ) during pre-monsoon season. Density in the whole study area varied from 10 to 

4820/ m 2 (av. 1040; m 2 ) during post-monsoon and 10 to 10090/m 2 (av. 2104/m2) 

during pre-monsoon season. At 30 m to 50 m zones an average biomass of7.38 glm 2 

102

and 6.08 g/m 2 were recorded during post-monsoon and pre-monsoon seasons 

respectively, which is comparable with the result of Joydas (2002) who reported a 

biomass of 8.3 g/m 2 in the 30-50 m depth zone for the continental shelf of entire west 

coast of India. 

Average density at the 30 m depth zone was 2654/m 2 and 1220/m 2 during 

post-monsoon and pre-monsoon seasons respectively. Average density reported by 

Prabhu et aI., (1993) in the 30 m depth zone off Gangolli, west coast of India was 

1725 and 1775 1m2 in the two consecutive years is comparable to the density reported 

during the present study. In the present study, average density observed at the 30 m 

and 50 m zone during pre-monsoon was 1922/m 2 , and was comparable with density 

0969/m 2 ) reported by Joydas (2002) in the 30-50 m zone of NW coast of India 

during same period. 

Since no similar works were available, present study was compared with data 

from other earliedr works. Neyman (1969) reported a biomass of 20 g/m 2 in the NW 

coast of India. Parulekar et al., (1982 a) reported an average biomass of 14.06 glm 2 

tor both macro and meio benthos together from the 20-40 m depth range. Parulekar et 

al., (1976) studied the quantitative aspects of benthos off Mumbai from 12 to 77 m 

depth and reported a low biomass values from nil to 4.63g/m 2 with no uniformity in 

the macrobenthic production. They reported an average of 1.1 g/m 2 in the study area 

olTMumbai. Harkantra et al., (1980) reported an average biomass of7.77 g/m 2 in the 

west coast from 30-70 m zone. Parulekar and Wagh (1975) recorded an average total 

biomass of 46.9 g/m 2 from 40-140 m depths stations in the NW coast of India. 

Parulekar et al., (1982a) observed an average biomass for both macro and 

meiobenthos was 12.39 glm 2 from 20-200 m. Qasim (1982) recorded a mean biomass 

of6.74g1 m 2 in the NW coast oflndia and biomass reported by Ansari et al., (1996) 

ranged from 10 to 100g/ m 2 with a mean of 20 g/ m 2 in the NW Indian shelf from 20 

to 350m depth. 

103

Difference in biomass and density noticed by earlier workers may be due to 

the use of different types of gears (Neyman, 1969; Parulekar and Wagh, 1975; 

Parulekar et al., 1976; Harkantra et al., 1980; Parulekar et al., 1982a; Qasim, 1982) 

or due to sampling in different seasons from diverse ecosystems (Ansari et al., 1996). 

In addition to the above reasons, biomass reported by Parulekar et al., (1982a) was a 

total of both macro and meiobenthos. The average biomass value (4.53g1m 2 ) for the 

study area as a whole during pre-monsoon season in the NW coast is well 

comparable to that of Joydas (2002) who reported an average value of 5.3g1 m 2 in the 

northwest coast of India during pre-monsoon. 

During post-monsoon biomass was generally high in shallow depths (30 m 

and 50 rn) and during pre-monsoon season it was high from 30 to 75 m and low in 

the deeper stations beyond 75 m. Density also followed more or less the same trend 

with high values in shallow stations and low in deeper depths in both seasons. This 

was in agreement with earlier reports (Kurian, 1953, 1967,1971; Neyman, 1969; 

Parulekar, 1973; Parulekar and Dwivedi, 1974; Parulekar and Wagh, 1975; Parulekar 

et al., 1976; Ansari et al., 1977b; Harkantra et al., 1980 & 1982; Parulekar et al., 

1982 b; Qasim, 1982; Devassy et al., 1987; Prabhu et al., 1993; Ansari et aI., 1996; 

Joydas and Damodaran, 2001). Enrichment of coastal waters due to riverine flow and 

land run off seems to be one of the factors contributing to richness of fauna in the 

nearshore regions (Parulekar, 1973). Devassy et al., (1987) reported high biomass in 

the near shore region and attributed it to the influx of nutrient rich river water. 

Influence of nutrient rich water is reported by other workes also (Kurian, 1971; 

Harkantra et al., 1980; Harkantra and parulekar, 1981 ). But the work of 

Gopalkrishnan and Nair (1998) recorded low benthic population in the nearshore 

areas (Srn) and rich fauna in 20 m contour of Mangalore. Ansari et al., (1996) also 

reported a decreasing standing crop with increasing depth and distance from the 

shore. They reported that neritic coastal waters of continental shelf (up to 200m 

depth) were often highly productive and many of the world's commercial fisheries 

104

were located in the nearshore waters. However they noticed an increase in the 

diversity of benthos in deeper waters as observed by Parulekar et al., (1992). High 

production reported by Devassy et al., (1987) in the near shore areas (5m depth) was 

also attributed to the variation in sediment texture. High biomass and numerical 

abundance in shallow depth zones can be due to high primary productivity 

(Radhakrishna et al., 1978). Parulekar and Wagh (1975) stated that Arabian Sea is 

charecterised by rich bottom fauna which is attributed to the inflow of equatorial 

waters of low salinity causing stratification in the water column. Low benthic 

biomass at higher depths is probably because of an inflow of subsurface water with 

low oxygen content. 

In the present study there was no obvious latitudinal variation in benthic 

biomass but comparatively high biomass values were observed in north in both 

seasons. This is in agreement with earlier reports of Neyman (1969), Humphrey 

(1972), Parulekar and wagh (1975), Parulekar et al., (1982a) and Ansari et al., 

(1996). As per the differential production in the south and north latitudes, Parulekar 

and Wagh (1975) demarcated the Arabian Sea shelf into two zones, one north of 20° 

N upto 23° and south of 20° N upto 17° Nand biomass in the Arabian Sea decreases 

gradually southward. Humphrey (1972) has attributed high phosphate content and 

higher primary production to the di fference in biomass production in the northern 

region as compared to the southern region. The rich bottom life in the Arabian Sea is 

attributed to rich plankton in the region enhanced by upwelling and intrusion of 

subsurface water during monsoon (Qasim, 1977). Neyman (1969) suggested that 15° 

N is the boundary between high and low productive zones. During pre-monsoon, off 

Ratnagiri showed an exceptional high biomass and density at 75 m depth. This 

variation observed may be due to the impact of localized biotic or abiotic factors or 

both. But Elizarov (1968) reported abundance of bottom life in the southern part of 

Arabian Sea and correlated the abundance to an inflow of equatorial waters of low 

salinity causing a strongly expressed stratification of water masses. Harkantra et al., 

105

(1980) also reported high values in shallow region with more diverse fauna in 

southern region of west coast and the difference may probably due to the influence of 

equatorial waters and upwelling. In the areas where ridges and sills develop low 

oxygen and high H 2S condition, the benthic biomass is either very impoverished or 

absent (Parulekar, 1986), However study of Joydas (2002) could not found any 

north-south variation in biomass in the west coast of India. 

Distribution of benthos showed a different pattern with higher population 

density in the southern latitude for both seasons as compared to the northern latitude. 

The change in trend could be due to variations in the size of the organisms. Usually 

population density and biomass are directly related but if the size variation among 

individuals is too large, the direct relation is lost. Parulekar and Ansari (1981) studied 

the macrobenthos of Andaman Sea and reported an inverse relationship between 

biomass and popUlation density. Ansari et aI., (1994) also reported that biomass did 

not follow the same trend as that of density due to the presence or absence of large 

sized organisms whilst Harkantra et al., (1980) observed a direct relation between 

benthic density and biomass except at few stations having large sized organisms in 

the west coast of India. 

The decrease of fauna towards deeper depths was influenced by environmental 

parameters like temperature, salinity and DO (Ingole et al., 2002; Parulekar and 

Ansari, 1981). Variation in temperature during pre-monsoon may influence the 

benthic popUlation. Ingole et al., (2002) reported temperature and salinity were 

regarded as regulators of the reproductive cycle of the marine invertebrates. Marine 

species inhabiting the tropical region generally have a narrow range of temperature 

tolerance since they normally live in a temperature regime that is close to their upper 

tolerance limit. The important variables controlling the distribution and abundance of 

benthic organisms in the tropical regime are salinity (Alongi, 1990; Parulekar and 

Dwivedi, 1974), and sediment stability (Wildish and Kristmanson, 1979; Warwick 

and Uncle, 1980). Seasonal variations observed in benthic production could be due to 

106

changes in the hydrographical and textural features. Harkantra and Parulekar (1981) 

also reported distinct seasonal changes in the benthos in the shallow depths off Goa. 

Present study showed an average meiobenthic biomass of 0.99 mg/lO cm2 

during post-monsoon and 4.77 mg/IOcm2 during pre-monsoon which is within the 

range of the earlier reports from the coastal waters of India (Damodaran, 1973; 

Parulekar et al., 1976; Rodrigues et al., 1982). Sajan (2003) studied the meiobenthos 

of west coast of India and reported a biomass of 1.27 mg/l0cm 2 in the northwest 

coast, which is more or less similar to the post-m on soon biomass value obtained in 

the present study. Average meiobenthic density in the present study was 169/IOcm 2 

during post-monsoon and 88611 Ocm 2 during pre-monsoon. Ansari et al., (1980) 

reported a density of 250-2925110cm 2 , which is higher than the present report. Sajan 

(2003) reported a density of 225/lOcm2 in the northwest coast of India which is 

closely similar to density of the post-m on soon season. 

Present study revealed high meiobenthic biomass and density in the shallow 

depths of all transects during post monsson season and at a few transects (ofT 

Monnugao and Mumbai) during pre-monsoon season. High occurrence of meiofauna 

in the shallow depths was in agreement with earlier reports (Parulekar et al., 1976; 

Ansari et ai., 1980;Rodrigues et al., 1982; Ansari and Parulekar, 1998; Sajan, 2003). 

Rodrigues et al., (1982) attributed the high meiobenthic biomass in the near shore 

region to the enrichment of coastal waters due to riverine flow and land runof( 

Fluctuations in the meiofaunal density and biomass at some stations may probably be 

as a result of graizing by macro fauna, or presumably because of the predator-prey 

relationship existing among meiobenthos itself (Mare, 1942). 

Present study showed that among meiobenthos, nematodes contributed more 

to the total biomass and population density. Mc Intyre (1969) suggested that 

nematodes were generally the dominant taxon in marine meiofauna. Parulekar et al., 

(1976) found that biomass was mainly represented by nematodes and density by 

foraminifers and nematodes. Ansari er al., (1980) reported dominance of nematodes 

107

followed by foraminifers while Rodrigues et al., (1982) reported dominance of 

nematodes followed by polychaetes. Ansari and Ingole (1983) and Sajan (2003) also 

noticed the dominance of nematodes followed by harpacticoides. The increased 

biomass and density in the shallow stations during pre-monsoon may be due to high 

surface productivity. 

Trend in meiobenthic distribution bctween transects was not disccrnible, but 

average values showed relatively high biomass and density along the northern 

transects. Neyman (1969) showed that benthos were sparse in the northern shelf of 

wcstern India at depths of 75-200m, attributing this to the low oxygen content in the 

water along the north. Present study reported dominance of nematodes among the 

other groups in shallow (95%) as well as deeper depths of 150 m depth (79%) even 

though density of total meiofaunal and nematodes decreased with depth. This can be 

explained by the tolerance capacity of nematodes in low oxygen conditions as 

observed by Damodaran (1973), Gooday et al., (2000) and Bernhard et al., (2000). 

Sajan (2003) reported 87% of the total meiofauna represented by nematodes beyond 

150 m. 

Present study showed that during post-monsoon macrobenthos and 

meiobenthos were more in the shallow depths than deeper depths reveals their 

positive relationships among themselves but Desai and Krishnankutty (1967) noticed 

an inverse relationship between macro and meiofauna. Average macrobenthic density 

was 1372/m 2 and 2104/m 2 during post-monsoon and pre-monsoon seasons 

respectively. Average density irrespective of seasons was I 738/m 2 . Average 

meiobenthic density during post-monsoon was 169/10 cm 2 (16900/m2) and during 

pre-monsoon it was 886/10 cm 2 (88600/m2). Average meiobenthic density 

irrespective of seasons was 52750/m 2 • The relation between macro and meiobenthos 

in the present study was in the ratio of 1 :30. Parulekar et al., (1976) reported an 

average ratio of macro to meiofauna was in the order of 1: 16,000 and opined that 

contribution of nematodes and foraminifers in the meiofauna seems to be the main 

108

factor for such a large difference in the faunal distribution. Rodrigues et ai., (1982) 

reported a population ratio of macro:meio fauna was I :91. Comparison of macro 

mciofauna ratios can indicate genuine differences in the utilization of particular 

habitats by the fauna. He also reported that ratio varies with the change in the 

sediment texture. Ansari et ai., (1982) reported that meiofauna was numerically 94- 

2193 times more than macrofauna with an overall contribution of 50 % to the total 

standing crop. Parulekar et al., (1992) reported a ratio of 1 :467 between macro and 

meiofauna. Ansari et al., (1977a) stated that relative proportion of macro to 

mciofauna was of the order of 1 :3500, which indicates the important role of 

meiofauna in the benthic community. High meiobenthic density in the present study 

reveals that meiobenthos is not limiting the macrobenthic production as that of 

surlacc primary production. 

109


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115

Transects 

30m 

Polychaetes Crustaceans Molluscs Miscellaneous 

group 

Total 

Off Monnugao 0.26 0.01 0.12 0.65 1.04 

Off Ratnagiri 0.41 0.02 0.42 0.01 0.86 

Off Mumbai 1.61 0.01 0.69 0.04 2.35 

OffVeraval 1.29 0.01 0.00 3.62 4.92 

Off Dwaraka 5.18 0.05 0.15 8.87 14.25 

Average 

50m 

1.75 0.02 0.28 2.64 4.69 

OtT Monnugao 8.80 0.00 0.00 0.17 8.98 

Off Ratnagiri 0.96 0.08 0.49 0.03 1.56 

Off Mumbai 14.00 0.10 0.09 1.68 15.87 

OffVeraval 2.68 0.01 0.00 0.76 3.45 

Off Dwaraka 6.61 0.05 0.15 0.66 7.46 

Average 

75m 

6.61 0.05 0.15 0.66 7.46 

Off Monnugao 0.83 0.02 1.58 0.17 2.60 

Off Ratnagiri 14.73 0.54 0.39 1.85 17.51 

Off Mumbai 2.83 0.08 0.46 0.03 3.40 

OffVeraval 0.77 1.00 0.00 2.25 4.02 

Off Dwaraka 5.03 0.26 0.14 1.29 6.72 

Average 

lOOm---_._._------ 

4.84 0.38 0.51 1.12 6.85 

OtT Monnugao 0.20 0.03 0.46 0.17 0.87 

Off Ratnagiri 1.77 0.03 0.10 0.14 2.04 

Off Mumbai 0.25 0.24 0.38 0.14 1.21 

OffYeraval 0.26 0.05 1.88 0.09 2.28 

OfT Dwaraka 3.58 0.04 0.24 0.09 3.95 

Average 

150m 

1.21 0.08 0.61 0.17 2.07 

Off Mumbai 0.82 2.90 0.27 1.87 5.86 

OffYerava! 0.00 0.03 1.72 0.0] 1.76 

OtT Dwaraka 1.51 0.67 0.23 0.26 2.67 

Average 

>t50m 

0.78 1.20 0.74 0.71 3.43 

OtT Mumbai 0.06 0.34 0.00 0.21 0.6] 

OffVeraval 0.02 0.00 0.00 0.00 0.02 

Average 0.04 0.17 0.00 0.11 0.32 

Table 6 - Macrobenthic biomass (g/m 2 ) during pre-monsoon season 

117

Traosects Polychaetes Crustaceans Molluscs Miscellaneous Total 

group 

30m 

Off Monnugao 4730 80 10 0 4820 

Off Ratnagiri 3810 90 40 80 4020 

Off Mumbai 1560 20 0 0 1580 

OffVeraval 2080 340 30 40 2490 

Off Porbandar 340 10 0 10 360 

Average 2504 108 16 26 2654 

50m 

Off Monnugao 1480 40 10 0 1530 

Off Ratnagiri 160 30 20 0 210 

Off Mumbai 340 0 60 0 400 

OffVeraval 3860 180 10 50 4100 


Average 1304 54 20 10 1388 

75m 

Off Mormugao 740 0 0 0 740 

Off Ratnagiri 932 ]0 0 0 942 

Off Mumbai 300 10 20 0 330 

OffVeraval 120 70 10 0 200 


Average 436 20 6 2 464 

lOOm 

Off Mormugao 680 70 20 0 770 


Off Mumbai 80 0 10 0 90 

OffVeraval 20 5 0 0 25 

Off Dwaraka 160 0 430 0 590 

Average 216 19 92 0 327 

lSOm 



Off Dwaraka 60 0 500 0 560 

Average 80 0 177 0 257 

Table 7 - Macrobenthic density (No/m2) during post-monsoon season 

118

Transects Polychaetes Crustaceans Molluscs Miscellaneous Total 

group 

30m 

OfT Mormugao 830 10 30 130 1000 

OfT Ratnagiri 260 10 290 10 570 

OfT Mumbai 1400 20 170 10 1600 

OfTVeraval 970 70 0 150 1190 

Off Dwaraka 1380 110 30 220 1740 

Average 968 44 104 104 1220 

SOm 

OfT Mormugao 5230 0 0 20 5250 

OfT Ratnagiri 490 70 110 40 710 

OfT Mumbai 2950 260 60 50 3320 

OfTVeraval 1070 10 0 130 1210 

Off Dwaraka 2435 85 43 60 2623 

Average 2435 85 43 60 2623 

7Sm 

Off Mormugao 840 30 160 20 1050 

Off Ratnagiri 8750 490 450 400 10090 

OfT Mumbai 3440 130 140 80 3790 

OffVeraval 430 50 0 50 530 

Off Dwaraka 1160 330 70 870 2430 

Average 2924 206 164 284 3578 

lOOm 

Off Mormugao 1860 20 180 20 2080 

Off Ratnagiri 1450 30 330 120 1930 

OITMumbai 1030 580 160 360 2130 

OffVeraval 1610 180 350 260 2400 

Off Dwaraka 1220 190 170 180 1760 

Average 1434 200 238 188 2060 

ISOm 

OflMumbai 1190 365 50 280 1885 

OfTVeraval 10 30 70 30 140 

Off Dwaraka 1550 170 50 30 1800 

Average 1080 273 73 67 1493 

>ISOm 

Off Mumbai 700 110 0 420 1230 

OfTVeraval 10 0 0 0 10 

Average 355 55 0 210 620 

Table 8 - Macrobenthic density (No/m2) during pre-monsoon season 

119

Miscellaneous 

Transects Nematodes Copepods group Total 

30m 

OfT Mormugao 0.53 0.00 0.13 0.66 

Off Ratnagiri 0.46 0.06 0.33 0.85 

OfT Mumbai 2.04 0.16 0.00 2.20 

OffVeraval 2.42 1.15 0.52 4.09 

OtT Porbandar 1.43 0.12 0.20 1.75 

Average 1.38 0.30 0.23 1.91 

% 72.0 15.6 12.3 

50m 

OtT Mormugao 0.44 0.06 0.13 0.63 

OfT Ratnagiri 0.94 0.12 0.33 1.39 

OfT Mumbai 0.84 0.09 0.20 1.13 

OffVeraval 0.47 0.09 0.65 1.21 

OfT Porbandar 0.29 0.06 0.20 0.55 

Average 0.60 0.09 0.30 0.98 

0/0 60.9 8.9 30.5 

75m 

OfT Mormugao 0.52 0.19 0.85 1.55 

OfT Ratnagiri 0.31 0.34 0.20 0.85 

Off Mumbai 0.12 0.09 0.13 0.34 

OffVeraval 0.08 0.37 0.20 0.65 

Off Porbandar 0.26 0.09 0.00 0.35 

Average 0.26 0.22 0.27 0.75 

0/0 34.5 28.9 36.4 

lOOm 

Off Mormugao 0.40 0.16 0.20 0.75 

Off Ratnagiri 0.08 0.22 0.20 0.49 

Off Mumbai 0.11 0.09 0.65 0.85 

OffVeraval 0.03 1.12 0.46 1.60 

Off Dwaraka 0.16 0.22 0.20 0.57 

Average 0.16 0.36 0.34 0.85 

% 18.4 42.3 39.8 

150m 

Off Ratnagiri 0.05 0.00 0.00 0.05 

Off Porbandar 0.03 0.00 0.00 0.03 

Off Dwaraka 0.02 0.00 0.13 0.15 

Average 0.04 0.00 0.04 0.08 

0/0 46.8 0.0 54.2 

Table 9- Meiobenthic biomass (mg/l0cm 2 ) distribution during pos-monsoon season 

120

Transects Nematodes Copepods Foraminifers M.G.* Total 

30m 

Off Monnugao 155 0 4 2 161 


Off Mumbai 600 5 15 0 620 

OffVeraval 713 37 12 8 770 

OffPorbandar 420 4 12 3 439 

Average 405 10 9 4 427 

0/0 94.8 2.2 2.1 0.8 

50m 



Off Mumbai 248 3 11 3 265 

OffVeraval 137 3 3 10 153 


Average 175 3 4 5 187 

0/0 93.8 1.5 2.2 2.5 

75m 

Off Monnugao 154 6 4 13 177 


Off Mumbai 35 3 3 , 43 


OffPorbandar 76 3 0 0 79 

Average 76 7 2 4 90 

0/0 84.9 7.8 2.7 4.7 

lOOm 



Off Mumbai 32 3 4 10 49 


Off Dwaraka 47 7 0 3 57 

Average 46 12 3 5 66 

0/0 69.9 17.6 4.6 7.9 

150m 



Off Dwaraka 7 0 0 2 9 

Average 11 0 2 1 13 

0/0 82.5 0.0 12.5 5.0 

Table 12 - Meiobenthic density (NolI 0 cm 2 ) distribution during post-monsoon 

(M.G.* - Miscellaneous group) 

122

Depths Nematodes Cope pods Foraminifers M.G* Total 

30 m 56.7 31.0 

SOm 24.6 9.0 

7S m 10.7 22.6 

lOO m 6.5 37.4 

ISO m 1.5 0.0 

--------------------------- 

44.4 

20.7 

11.8 

14.8 

8.2 

19.7 

25.2 

23.0 

28.5 

3.6 

Table 13 - Percentage contribution of meiobenthic groups in different depths 

M. G* - Miscellaneous groups 

Transects Depths Nematodes Foraminifers Cope pods M.G* 

Off Mormugao 30m 46 12 0 33 

75m 136 34 0 67 

lOOm 1740 624 0 27 

Off Ratnagiri 30m 177 0 2 34 

75m 77 7 0 19 

Off Mumbai 30m 170 0 0 108 

75 m 1506 886 50 241 

OffVeraval 30m 338 14 11 10 

75m 91 90 13 18 

Off Dwaraka 30m ]23 13 11 25 

75m 102 52 2 10 

100 m 89 16 0 5 

Average 383 146 7 50 

'10 65.34 24.86 1.27 8.49 

Table 14 - Distribution of meiobenthic density (NolI 0 cm 2 ) during pre-monsoon 

M. G* - Miscellaneous groups 

54.5 

23.9 

11.5 

8.4 

1.7 

Total 

--- 

91 

237 

2391 

213 

103 

278 

2683 

373 

212 

172 

166 

110 

586 

123

Biomass 

30m 50m 75m lOOm 150m 

----_ .. _--- 

Polychaetes 1.1841 (8) 0.4478 (7) 1.6782 (8) 1.1021 (8) 0.5432 (6) 

Crustaceans 1.5840 (8) 1.2902 (7) 1.4058 (8) 1.0498 (8) 0.7928 (6) 

Molluscs 0.9181 (8) 1.5868 (7) 0.8002 (8) 0.4768 (8) 0.2453 (6) 

Others 0.2671 (8) 1.5153 (7) 2.4222 (8) 0 0 

Total 0.9426 (8) 0.1568 (7) 2.1625 (8) 0.8501 (8) 1.0104 (6) 

Density 

Polychaetes 1.8842 (8) 0.1847 (7) 1.5981 (8) 6.4973 (8) 1.4782 (6) 

Crustaceans 1.0106 (8) 0.4817 (7) 2.0775 (8) 0.7676 (8) 1.2390 (6) 

Molluscs 1.58 (8) 0.8589 (7) 2.0532 (8) 1.5429 (8) 1.0968 (6) 

Others 1.7746 (8) 2.0786 (7) 1.7438 (8) 0 0 

Total 1.7209 (8) 1.2604 (6) 1.7981 (8) 9.4887 (8) 1.3558 (6) 

Table 15- Seasonal comparison ofmacrobenthic biomass and density based on Student's t 

test in different depths (Degree of freedom is given in bracket). 

12

Wagh, 1975; Parulekar et ai, 1976; Ansari et ai, 1977; Harkantra and Parulekar, 

1981; Devassy et ai, 1987; Varshney et ai, 1988; Vizakat et ai, 1991; Harkantra and 

Parulekar, 1991 & 1994; Prabhu et ai, 1993; Gopalakrishnan and Nair, 1998 and 

Ingole et ai, 2002). Parulekar et al (1982), Ansari et al (1996) have attempted to 

study the benthos from the deeper depths of Indian EEZ. Later, Joydas (2002) and 

Sajan (2003) worked on the macro and meiobenthos from the west cost of India 

respectively. 

6.2. Results 

Depth wise and transect wise variations m the faunal composition of 

northwestern continental shelf of India are examined and discussed in this chapter. 

The description is presented in three parts. The first part deals with results of faunal 

composition during post-monsoon and pre- monsoon periods. Second part describes 

the community structure analysis of polychaetes and all groups including 

polychaetes. Third part of the result deals with the similarity indices for both the 

seasons. 

Based on their occurrence benthic organIsms were differentiated into 3 

catregories such as 'abundant', 'moderately abundant' and 'rare'. The 'abundant' are 

those organisms present in more than 75% of the total stations sampled in each depth 

zone and 'moderately abundant' are those occurred in 25-75% of the stations and the 

remaining is considered as 'rare'. 

6.2.1. Faunal composition 


Fauna composed of polychaetes, crustaceans, molluscs and miscellaneous 

groups (Plates 5-8). Percentage contribution of each group is given in Fig. 35. 

Polychaetes constituted 86% followed by molluscs (9%) and crustaceans (4%). 

Miscellaneous groups formed only 1 % to the total population. Other than 

131

polychaetes, crustaceans contributed substantially along most transects except ofT 

Mumbai and Porbander where molluscs dominated. 

Percentage contribution of various polychaete families is presented in Table 

16. Polychaetes were composed of errantia (6%) belonging to 10 families and 

sedentaria (94%) belongigng to 14 families. Eunicidae (2.8%) and Pilagidae (1.2%) 

were the major families in Errantia. Other important families among errantia were 

Nephtydae (0.58%), Aphrodite (0.53%), Glyceridae (0.41 %) and Pisionidae (0.27%). 

Among 14 sedentarian families, Spionidae was the dominant one (64.2%) followed 

by Magelonidae (10.3%), Cirratilidae (5.1 %), Cossuridae (5%), Capitellidae (3.6%), 

Paraonida (2.2%) and Stemaspidae (1.2%). Of the 76 species present during post 

monsoon, 25 species belonged to errantia and 51 species to sedentaria. 

Depth wise percentage occurrence of polychaete species is presented in Table 

17. At 30 m depth zone, 37 species were present of which 8 species were coming 

under errantia and 29 under sedentaria. Of the 37 species, 6 species were considered 

as 'abundant' (Prinospio pinnata, P. polybranchiata, Magelona capensis, Cirratulis 

cirra/us, Cossura coasta and Capitella capitata) and 12 were 'moderately abundant' 

of which Ancystrosyllis constricta, Lumbrineries aberans, Prinospio cirri/era, 

Magelona cincta and Heteromastus bifidis were the major ones (i.e., present in more 

than 50% of the stations). The remaining 19 species were considered as 'rare'. 

Species contributed more to the total density were Cossura coasta (6100/m 2 ), 

Magelona cincta (5800/m 2 ), and Prinospio cirri/era (5400/m 2 ). 

At 50 m zone altogether 34 species were present, composed of II errantia and 

23 sedentaria. Among these, 7 were regarded as 'abundant' (Ancystrosyllis 

cons/rieta, Prinospio pinnata, P. polybranchiata, P. cirri/era, Cirratulis cirratlls, 

Cossura coasta and Capitella capitata) and 10 species were treated as 'moderately 

abundant' of which Lumbrineries aberrans, L. hartmani, Prinospio ehlersi, 

Magelona capensis, Paraheteromastus tenuis and Sternaspis scutata were the major 

132

ones and 17 were included in the 'rare' catogery. Dominant species were Magelona 

cincta (8000/m 2 ), Prinospio sexoculata (7400/m2) and Magelona capensis (3900/m 2 ). 

At 75 m zone, 59 species were present of which 19 belonged to errantia and 

40 to sedentaria. Of the 59 species, 4 were 'abundant' (Prinospio pinnata. P. 

polybranchiata. P. cirrifer and. Cossura coasta), and 18 were 'moderately abundant' 

of which Ancystrosyllis constricta. Malacoceros indicus, Magelona cincta. Cirratulis 

cirratus and Scolariella dubia were the important ones and 37 were 'rare'. Prinospio 

cirri/era (l700/m 2 ), Malacoceros indicus (l200/m 2 ), Prinospio polybranchiata and 

Cirratulis cirratus (llOO/m 2 each) and Sthenelais boa (lOOO/m2) were the major 

contributors to the total density. 

At 100 m zone, 27 species were present; of which 8 were from errantia and 

19 from sedentaria. Only one species could be considered as 'abundant' in this zone 

(Prinospio pinnata) and 10 species as 'moderately abundant'. Among the moderately 

abundant species the major ones were Glycera longipinnis, Lumbrineries hartmani. 

Prinospio polybranchiata. P. cirrifera. Cirratulis cirratus and Capitella capitata. 

Sixteen species were considered as 'rare'. In this zone Pygospio elegans (l500/m2) 

and Prinospio polybranchiata (1300/m2) were the dominant species. 

At 150 m zone, six species were present including one errantia and 5 

sedentaria. An exception from the other depth zones, all the 6 species recorded were 

considered as 'moderately abundant' which includes Ancystrosyllis conslricla, 

Prinospio pinnata. P. polybranchiata. Cirratulis chrysoderma, Paraonides lyra lyra 

and Cossura coasta of which P. pinnata and C. coasta were the major ones. C. 

coasta (10001 m 2 ) is the only species which contributed more to the total density in 

this zone. 

Among the non-polychaete taxa, crustaceans were mainly constituted by 

decapods and amphipods; molluscs by pelecypods and miscellaneous groups by 

sipunculoides. Here also occurrence of different groups were categorized to 

133

'abundant', 'moderately abundant' and 'rare'. Percentage occurrence of each group is 

presented in Table 18. 

At 30 m zone, a total of 18 groups/species were found, of which 2 groups 

were considered as 'abundant' (decapod species and carridian prawns), 6 groups as 

'moderately abundant' of which megalopa larvae and sipunculids were major ones 

and ten groups were considered as 'rare'. 

At 50 m depth zone, 14 groups were present, and none could be included in 

the 'abundant' category, and the only one 'moderately abundant' group/species was 

bivalve Tellina sp, and rest of them were regarded as 'rare'. 

At 75 m depth 8 groups were present and 'abundant' group was absent and 

only one taxa was considered as 'moderately abundant' (caridian prawns) and rest of 

the 7 groups were included in the 'rare' category. 

At 100 m zone 15 groups were present of which 4 were 'moderately abundant' 

which included cardiun sp., mactra sp., decapod sp. and lobster. Eleven groups were 

considered as 'rare' and no group occurred as 'abundant'. 

At 150 m zone, 4 groups were present of which bivalve Tellina sp. was 

'abundant' and 3 groups/species (bivalves Cardium sp, Mactra sp. and Sunetta 

scripta) were 'moderately abundant' and 'rare' species were absent. 

6.2.1.2. Pre- monsoon 

During pre- monsoon, polychaete contributed 80% followed by miscellaneous 

groups (7%), crustacean (7%) and molluscs (6%) to the total fauna (Fig. 36). In all 

transects, molluscs dominated among non-polychaete groups except off Mumbai and 

Porbander where crustaceans and miscellaneous groups dominated respectively. 

Polychaetes were composed of errantia and sedentaria. The former constituted 

only 28.3% and latter formed 71.7% to the total polychaetes density (Table 19). A 

[otal of 33 families were encountered of which errantia comprised of 13 families and 

sedentaria of 20. Of the 13 errant families Pilargidae (7.8%) and Eunicidae (6.6%) 

Ilere dominant. Other major families were Syllidae (4.8%), Aphroditidae (4.2%) and 

134

Nephtydae (2%). Among the 20 sedentarians families Cirratulidae contributed 

maximum (19.7%) to the total density followed by Spionidae (15.2%), Capitellidae 

(7.2%), Ampharetidae (8.3%), Cossuridae (5%) and Terebellidae (3.6%). Of the total 

133 polychaete species encountered, errantia was represented by 43 species and 

sedentaria by 90 species. 

Depth wise occurrence of different polychaetes species is presented in Table 

20. At 30 m depth zone, 52 species were present of which 12 species were of errant 

type and 40 were sedentarian. Of the 52 species, 6 species were considered as 

'abundant' (Ancystrosillis constricta, Lumbrineries hartmani, Prionospio pinnata, P. 

po(vbranchiata, Cossura coasta and Capitella capitata) and 21 species were 

'moderately abundant' among which Nephtys dibranchis, Prionospio cirrobranchia, 

P. cirrifera, Magelona cincta, Ciriformia ajer, Heteromastus bifidis, Notomastus 

fauvelli, Schyphoproctus sp. and Sternaspis scutata were the major ones (present> 

50% of the stations). The remaining 25 species can be considered as 'rare'. In this 

zone, species which contributed more to the total density were Cossura coasta 

(730/m2), Prionospio pinnata (600/m2), P. polybranchiata (530/m2), and Sternaspis 

scutata (490/m2) 

At 50 m zone, 58 species were obtained of which 18 species were errant forms 

and 40 were sedentarians. Of the 58 species, 8 were 'abundant' (Ancistrosyllis 

constricta, Nephtys dibranchis, Lumbrineries aberrans, Prinospio pinnata, P. 

polybranchiata" Cossura coasta, Capitella capitata and Sternaspis scutata) and 50 

were 'moderately abundant' of which Glycera longipinnis, Lumbrineries hartmani. 

Prinospio cirrobranchiataa, P. cirrifera, Magelona cincta, Cirratulis cirratus, 

Cirriformia afer, Paraonides lyra lyra , Aricidea fauveli, Notomastus abberans, 

Paraheteromastus tenuis, Amphictius gunneri, and Etione sp. were the major ones 

and no species could be considered as 'rare'. In this depth zone Ancistrosyllis 

135

constricta (920/m2), Prionospio pinnata (820/m2), Cirratulis aler (J8l0/m2) were 

the dominant species. 

At 75 m zone a total of 72 specIes were present, among which errantia 

constituted 26 species and sedentaria 46 species. Of the 72 species, 10 species were 

considered as 'abundant' which included Ancistrosyllis constricta, Prionospio 

pinna ta, P. cirrobranchia, P. cirri/era, Magelona cincta, Cirratulis cirratus, 

Cirriformia aler, Cossura coasta, Maldane sarsi, and Amphicteis gunneri. In the 

'moderately abundant' group, 18 species were noticed of which Nephtys dibranchis, 

Gonioda emerita, Lumbrineries hartmani, Prinospio polybranchiata and Capitella 

capitata were the major ones. The 'rare' ones included 44 species. In this zone 

Cirratulis cirratus (l710/m2) and C. chrysoderma (l280/m2) were the dominant 

specIes. 

At 100 m zone, a total of 66 species were recorded, errantia constituted by 24 

species and sedentaria represented by 42 species. Of the total 66 species, 9 species 

were regarded as 'abundant' which included Ancistrosyllis constricta, Prionospio 

pinnata, P. cirrifera, Magelona cincta, Cirratulus cirratus, Tharyx sp., Capitella 

capitata, Notomastus aberans, and Amphicteis gunneri. Nine species were 

'moderately abundant' (Nephtys dibranchis, Prionospio cirrobranchiata, Cirriformia 

a/er, Cossura coasta, Syllis spongicola, Lumbriconeries aberrans, L. hartmani, 

Heteromastides bifidus and Maldane sarsi), and as many as 48 species were found to 

be 'rare'. Species such as Notomastus aberrans (J 1 lO/m2), Cirratulus cirratus 

(BOO/m2), Prinospio pinnata (560/m2) and Ancistrocyllis constricta (660/m2) 

contributed more to the total density. 

At 150 m depth zone, only two stations could be sampled and 39 species were 

present of which 12 belonged to errantia and 27 to sedentaria. Of the 39 species 

encountered in this zone, only one species, Cossura coasta was considered as 

ilb

At 75 m zone, 31 groups/species were present of which 3 were 'abundant' 

such as decapod larvae, amphipod Eriopisa chilkensis and sipunculids. Thirteen 

groups/species were 'moderately abundant' of which amphipod Grandidierella 

gilesi, species of Anthurid, bivalve Sunetta scripta, oligochaetes, nematods and 

nemertene worms were the major ones. Fifteen groups/species were considered under 

'rare' category. 

At 100 m zone, 41 groups/species were present of which 5 were 'abundant' 

(decapod larvae, amphipod Grandidierella gilesi, gastropod Nassarius sp., 

nematodes, and sipunculids) and 17 were moderately occurring of which Atys sp. and 

olygochaetes were important ones and 19 groups/species were considered as 'rare'. 

At 150 m zone, 28 groups/species werepresent of which 2 (decapods an nematodes) 

were abundant and 26 were moderatly abundant. Beyond 150m depth, 9 

groups/species were presnt and all were moderatly abundant. 

6.2.2. Community structure 


6.2.2.1.1. Community structure of Polychaetes 

Community structure indices of polychaete species (Table 22) in the study 

area varied from 1 to 41. More number of species as well as higher ahundance was 

observed in the southern transects where number of species varied from 4 to 41 and 

abundance (density) varied from 80 to 4730 /m 2 compared to the northern transect 

stations where species number varied from 1 to 23 and abundance varied from 30 to 

3860/ m 2 . 

6.2.2.1.1.1. Species richness (Margalef's index, d) 

Depth wise average of community structure indices based on polychaete 

species during post-m on soon season is presented in Fig. 37. Average values of 

species richness increased from 30 m to 75 m and tllen decreased (Fig. 37a). In 

southern transects, relatively high richness was observed and Margalef index varied 

138

etween 0.68 and 5.85 and in northern transects generally lower richness was 

observed which varied between 0.29 and 2.88 (Table 22). Transect wise richness in 

different depth zones presented in Fig. 38 showed that at 30 m zone richness was 

fluctuating transect wise and highest richness was observed off Veraval followed by 

Ratnagiri and lowest off Porbandar. At 50 m zone, richness first increased up to off 

Mumbai then decreased to Porbandar with highest richness off Mumbai and off 

Veraval, and lowest off Mormugao. At 75 m depth zone, high richness was observed 

in the southern transect stations and low in the northern transect stations. Maximum 

richness was observed off Ratnagiri from where richness decreased towards the north 

and minimum richness was observed off Porbandar. At 100 m depth zone species 

richness decreased towards north except off Dwaraka where a slight increase was 

observed. Highest value was observed off Mormugao and lowest off Veraval. At 150 

m depth also, even though, richness was low, high value was observed off Ratnagiri 

and low value off Porbandar and no richness was observed off Dwaraka. In general, 

comparatively high richness was observed in the southern transect especially after 50 

m depth. 

6.2.2.1.1.2. Evenness (Heip's index, J') 

Depth wise average values in the study area showed that (Fig. 37b) evenness 

was generally increasing from 30 m to 75 m depth then decreased however high 

evenness was observed at greater depths beyond 50 m. Evenness in the southern 

transects showed a higher uniformity in the distribution of individual organisms 

among the various species and ranged between 0.21 and 0.96 (Table 22). Uniformity 

observed was close to the maximum uniformity at most of the stations. In northern 

transects also a closeness to the maximum uniformity in the distribution of total 

abundance among various species was observed and evenness ranged from 0.48 to 

0.98. In the study area average evenness was 0.78 with very low variation (C. V. %= 

28.15%). Evenness distribution in different depth zones showed that (Fig. 39), at 30 

m zone, evenness increased to north with lowest value off Mormugao and highest ofT 

139

Porbandar. At 50 m depth zone, fluctuating results were observed with lowest value 

otT Veraval and highest off Mumbai. At 75 m depth zone, generally high evenness 

was observed with an increasing trend towards north. Lowest value was observed off 

Monnugao and highest off Veraval and Porbandar. At 100 m zone, comparatively 

high evenness was observed with the lowest value off Mormugao and highest ofT 

Dwaraka. At 150 m zone, high evenness was noticed off Ratnagiri and low values 

were recorded off Porbandar. Comparison with off Dwaraka was not possible due to 

the occurrence of only single species. In general evenness was fluctuating however, 

high evenness was observed in the northern transect (OffDwaraka). 

6.2.2.1.1.3. Diversity (Shannon index. H') 

Average values showed that diversity generally increased up to 75 m and then 

decreased with a drastic fall in 150 m zone (Fig. 37c). Regarding the species 

diversity, a pattern similar to species richness was obtained. Diversity and ranged 

between 0.7 and 4.92 in the southern transects (Table 22) and in the northern 

transects, at all stations diversity was less than that of southern transects but more 

stable and ranging between 0.92 and 3.38. For the study area average diversity 

obtained was 2.53 with very low spatial variation (c. V. % = 47.63%). Diversity 

distribution in different depth zones showed (Fig. 40) fluctuating results at 30 m 

depth zone, however high values observed in northern transect with lowest diversity 

otT Monnugao and highest off Veraval. At 50 m depth, even though diversity was 

fluctuating, comparatively high value was observed in the southern transect. At 75 m 

depth zone, diversity decreased towards north. Highest diversity was observed off 

Ratnagiri and lowest off Porbandar. At 100 m depth also, a decreasing trend was 

observed towards north except a high value off Dwaraka. Highest diversity was 

recorded ofT Mormugao and lowest off Veraval. At 150 m depth zone, high diversity 

was observed off Ratnagiri and low off Porbandar and no diversity off Dwaraka due 

to the presence of single species. In general, diversity in different depth zones 

showed a general decrease towards north beyond 50 m depth. 

1'10

H2./.l.4. Dominance (Pie/ou's index) 

Average values showed that dominance was decreased from 30 m to 75 m 

depth then it increased to deep with highest value at 150 m depth (Fig. 37 d). Very 

low species dominance was observed in the southern transects (ranged from 0.04 to 

0.82) in most of the stations whereas in the northern transects, most of the stations 

comparatively higher values were noticed (ranged from 0.1 to 1.0) thus showing an 

inverse relationship with species richness and diversity in general. Species 

dominance was very low (X = 0.31) with high spatial variation (C.V. %= 82.43%). 

Dominance at different depth zones showed that (Fig. 41) at 30 m zone, eventhough 

dominance was fluctuating with transect, relatively high dominance was observed in 

south and decreasing to north with ofT Mormugao having highest value followed by 

off Mumbai and lowest ofT Veraval. At 50 m zone, it was fluctuating with 

comparatively high dominance off Veraval and low off Mumbai. At 75 m depth, a 

slight increase in dominance was observed towards north with minimum value found 

offRatnagiri and maximum value off Porbandar. At 100 m zone, a similar trend was 

observed with an increasing dominance towards north except ofT Dwaraka. Lowest 

dominance was observed off Mormugao and highest ofT Veraval. At 150 m depth 

lone, an increasing trend was noticed towards north as that of 75 m and 100 m zone 

with lowest dominance observed off Ratnagiri and highest ofT Dwaraka. The 

dominance observed ofT Dwaraka was due to the presence of a single species. In 

general increased dominance was observed in the northern transect. 

6.2.2.1.2. Community structure of groups 

Community structure of groups showed that number of groups varied from 

to 10 with benthic abundance of 40 to 4820. In the southern transects number of 

species varied from 1 to 10 and density varied from 90 to 4820/m 2 and in the 

northern transects number of species varied from 2 to 7 and density varied from 40 to 

4100/m2. 

141

otTMumbai and Ratnagiri and low evenness in the rest of transects. At 75 m depth 

rone, comparatively high evenness was observed off Veraval and low off Ratnagiri. 

Due to the presence of a single species no evenness could be calculated ofT 

Monnugao. At 100 m depth zone a general increase in evenness towards north with 

highest value ofT Dwaraka and lowest off Monnugao. At 150 m depth zone, evenness 

was more off Porbandar and low off Dwaraka and Ratnagiri. In general high 

evenness was observed in the northern transect stations. 

6.2.2.1.2.3. Diversity (Shannon index, H') 

Depth wise average values showed that diversity increased towards deeper 

zones with minimum value at 30 m depth zone and maximum at 100 m zone (Fig. 

42c). In the southern transects diversity varied from 0.08 to 1.25 and in the northern 

transects it varied from 0.19 to 1.40 (Table 23). Diversity distribution in various 

depth zones is presented in Fig. 45. Transect wise diversity showed that, at 30 m 

depth zone, it was fluctuating with comparatively high value offVeraval and low off 

Mumbai. In 50 m depth zone also fluctuating trend was observed. High diversity was 

recorded off Ratnagiri and it decreased towards north and minimum diversity was 

observed ofT Porbandar. At 75 m depth zone, comparatively high diversity was 

observed at north with maximum value off Veraval and minimum ofT Ratnagiri. No 

diversity could be calculated off Monnugao due to lack of non-polychaete taxa. At 

lOO m depth zone, diversity reduced from off Monnugao to off Mumbai thcn 

increased to off Dwaraka with highest diversity recorded ofT Dwaraka and lowest off 

Mumbai. At ISO m depth zone, diversity was more off Porbandar and low off 

Dwaraka and Ratnagiri. In general, diversity among different transects fluctuated 

however, northern transects recorded comparatively higher diversity. 

6.2.2.1.2.4. Dominance index (Pie/ou's index, A') 

Depth wise average values showed that dominance generally decreased to 

deep with maximum value at 30 m depth zone and minimum at 100 m zone (Fig. 

42d). Dominance in the southern transects varied from 0.59 to 1.0 and in the northern 

143

uansects stations it varied from 0.45 to 0.94 (Table 23). Transect wise dominance 

distribution in various depth zones is presented in Fig. 46. At 30 m depth zone, high 

dominance was observed at most transects, especially in the southern transects with 

maximum dominance off Mumbai and minimum off Veraval. At 50 m depth zone, 

dominance was fluctuating, with highest value observed off Mormugao and 

Porbandar and lowest off Ratnagiri. At 75 m depth zone, high dominance was 

observed at southern transects and low in the northern transects. Highest dominance 

was observed off Mormugao (due to a single group, polychaete) and lowest off 

Veraval. At 100 m depth zone also, high dominance was observed in the southern 

lra/1sects and low in the northern transects. Maximum value was observed off 

Mumbai and minimum off Dwaraka. At 150 m depth zone, more or less similar 

dominance was observed with a slight decrease off Porbandar. In general dominance 

was more in the southern transect stations than northern transect stations. 


61.2.2.1. Community structure of Polychaetes 

Community structure indices of polychaete during pre-monsoon season 

(Table 24) showed that number of species varied from 7 to 50 and abundance 

varied from 290 to 8825in the southern transects. More number of species as 

well as higher abundance was observed in the southern transects. In the 

northern transect stations least number of species observed and it varied 

between 1 to 34 and abundance varied from 50 to 1700. 

6.2.2.2.1.1. Species richness (Margalef's index, d) 

Depth wise of average species richness at different depth zones based on 

average values is presented in Fig. 37a. Average values showed that richness was 

more in the 75 'm followed by 100 m zones and low in the other depth zones and 

drastically reduced beyond 150 m. Species richness varied from 0.89 to 5.39 in the 

southern transect and 0.19 to 4.55 in the northern transects (Table 24). Average 

richness for the study area was 2.67 with high variability of 464.36%. Transect wise 

144

species richness at each depth zones is presented in Fig. 38. At different depth zones, 

richness was generally more in the northern transect stations and northward increase 

in the species richness was obvious in the 30 m depth zone. In 50 m zone, transect 

wise trend was fluctuating with high values off Mormugao and Mumbai and low off 

Ratnagiri. In 75 m zone, Ratnagiri recorded high species richness and off Mumbai 

the lowest. At 50 m and 75 m depth zones even though species richness was 

fluctuating, comparatively high average values were observed in the northern transect 

stations. At 100 m zone, a northward increase was observed and at 150 m zone, only 

3 observations were made and richness fluctuated with relatively high value ofT 

Dwaraka. In > 150 m zone, since only two observations were done no comparison 

was possible. Generally during this season northern transect stations recorded high 

species richness especially at 30 and lOOm depths. 

6.2.2.2.1.2. Evenness index (Heip's index, J') 

Average values showed high evenness In the lower depths and a general 

decrease towards deeper depths with highest value at 30 m and lowest at > 150 m 

(Fig. 37b). Species evenness was more consistent in the southern transect with least 

value of 0.64 and highest value of 0.95 (Table 24). Since this index measures the 

closeness to maximum evenness, it could be stated that stations with highest 

evenness value, distribution is more close to the maximum uniformity. In the 

northern transects, this index varied between 0.28 and 0.90. Average evenness in the 

in the study area was 0.73 which is also high indicating a less dominance tendency 

for Polychaetes species. Since Heip's index varied over a large scale, the spatial 

variation was very high (C. V. %=462.77%). Transect wise evenness distribution in 

each depth zones (Fig. 39) showed that at 30 m zone, evenness was fluctuating with 

highest value off Ratnagiri and lowest off Mormugao. At 50 m depth zone also 

evenness was fluctuating as that of previous zone and high evenness was observed 

off Ratnagiri and low off Mormugao. At 30 m and 50 m zones, even though trend 

was fluctuating, average values showed comparatively high evenness in the northern 

14')

transect stations. At 75 m zone also evenness was fluctuating with comparatively 

high evenness observed in the northern transect stations than southern transect 

stations. Maximum evenness was observed otT Veraval and minimum otT Mumbai. 

At 100 m zone, northern latitude stations observed comparatively high evenness and 

southern transect stations otT Monnugao and Ratnagiri had low evenness. At 150 m 

zones, high evenness was observed off Mumbai and Porbandar but low off Veraval. 

Beyond 150 m depth, only 2 observations made, and no comparison was possible. In 

general, at most of the depth zones comparatively high evenness was observed in the 

northern transect stations. 

6.1.2.2.1.3. Species diversity (Shannon index, H') 

Depth wise average diversity for polychaete species (Fig. 37c) showed that it 

was generally high from 30 m to 100 m depth zones and beyond 100 m zone 

diversity reduced sharply with maximum diversity at 75 m. Species diversity showed 

a more consistent pattern of distribution in southern transects than northern transects 

(Table 24). In the southern transects it ranged between 1.84 and 4.35. In the northern 

transects relatively high diversity was observed in most of the stations than southern 

transects and it varied from 0.28 to 4.38 and showed a more patchy distribution 

(Table 24). Average diversity for the study area was 3.14 with high spatial variation 

(C. V. % =463.43%). Transect wise diversity distribution in each depth zones is 

given in Fig. 40. At 30 m zone a gradual increase towards north was observed with 

minimum diversity otT Monnugao and maximum otT Dwaraka. At 50 m depth zone, 

more or less similar diversity was observed in most transects with high value off 

Mumbai and exceptionally low value off Ratnagiri. At 75 m depth zone, diversity 

was fluctuating along transects and maximum diversity was observed off Ratnagiri 

and minimum otT Mumbai. At 100 m zone, a general increasing trend was noticed 

towards north with lowest value otT Monnugao and highest otT Veraval. At 150 m 

zone also northern latitude station (off Dwaraka) recorded maximum diversity. 

Exceptionally low diversity met with otT Veraval as an exception from the previous 

146

E2.2.2.!. Richness (Margalef's index, d) 

Depth wise average richness based on groups is presented in Fig. 42a. Group 

wise richness showed slightly different trend as that of species richness with high 

average richness in the deeper depth except at > 150 m. Group richness in the 

southern transects varied from 0.12 to 1.53 and in the northern transects it varied 

from 0.7 to 1.61 (Table 25). Transect wise richness in different depth zones is 

presented in Fig. 43. Results showed that at 30 m zone, richness was more in the 

northern transect stations than in the southern transect stations and the highest value 

was observed off Dwaraka and lowest off Mumbai. At 50 m zone, with an 

exceptional low value off Mormugao, richness decreased from ofT Ratnagiri to 

veraval. At 75 m depth, richness was fluctuating with maximum value observed ofT 

Mumbai and minimum ofT Veraval. Average values showed more or less similar 

richness in the southern and northern transect stations at this depth zone. At 100 m 

depth zone, richness was more in the northern transects than in the southern transects 

with lowest value ofT Mormugao and highest off Dwaraka. At 150 m depth, 

comparatively high richness was observed off Mumbai and low off Dwaraka with a 

general decrease towards north. Below 150 m depth no comparison was possible due 

to insufficient observation. Generally, at 30 m and 100 m depth zones, richness was 

more in the north and in 50 m and 150 m it was more in south and at 75 m zone it 

was more or less similar in northern and southern transects. 

62.2.2.2.2. Evenness (Heip's index, J ') 

Evenness was low in shallow depths and comparatively high evenness was 

observed beyond 75 m depth zone (Fig. 42b). Evenness in the southern transects 

varied from 0.04 to 0.69 and in the northern transects it varied from 0.27 to 0.81 

(Table 25). Transect wise evenness distribution in different depth zones showed that 

(Fig. 44) at 30 m depth zone, slightly higher values were observed off Mormugao, 

and Ratnagiri and low values in the rest of transects. At 50 m depths, fluctuating 

results were observed, with high value off Ratnagiri and low values off Mormugao. 

148

Average values of northern and southern transect stations showed more or less 

similar values in both areas. Low evenness was observed at 75 m depth zone, with 

comparatively high values in the northern transect stations. In 100 m zone, 

fluctuating trend was observed, and average values showed comparatively high 

evenness in the northern transect stations. At 150 m zone, evenness varied with 

transects and comparatively high value was observed off Veraval and low value off 

Dwaraka and off Mumbai. In > 150 m zone, no comparison was possible due to 

insufficient observation. In general, no regular transect wise trend was observed. 

6.2.2.2.2.3. Diversity (Shannon index, H') 

Depth wise average values showed that diversity was more in the deeper depth 

zones with highest value in 150 m zone and lowest in 50 m zone (Fig. 42c). Diversity 

in the southern transects varied from 0.04 to 2.27 and in the northern transects it 

varied from 0.71 to 2.26 (Table 25). Transect wise diversity distribution in different 

depth zones showed that (Fig. 45) at 30 m depth zone, generally northern transect 

stations have comparatively high diversity than southern transect stations however, 

maximum (off Ratnagiri) and minimum (off Mumbai) values met with southern 

stations only. At 50 m zone, with an exceptionally low diversity observed off 

Mormugao, generally diversity decreased to north with minimum value off 

Mormugao and Dwaraka and maximum off Ratnagiri. At 75 m depth zone, northern 

transect generally noticed higher diversity and southern transect low diversity with an 

exceptional high diversity off Monnugao. Lowest value was found off Mumhai and 

highest value off Dwaraka. At 100 m depth zones, with an exceptional high diversity 

observed otT Mumbai, diversity increased towards north. Minimum diversity was 

observed off Mormugao and maximum off Mumbai. At 150 m depth zone, diversity 

was fluctuating and maximum was observed off Veraval and minimum off Dwaraka. 

At >150 m zone, no comparison was possible due to insufficient samples. In general, 

northern transect showed more diversity as that of species.

I ):.2.2.2.4. Dominance (Pie/ou's index) 

Depth wise average values showed that dominance was low at 100 m and 150 

, m and high in the rest of the depth zones, especially at 50 m zone (Fig. 42d). 

: Dominance in the southern transects varied from 0.31 to 0.99 and in the northern 

I 

I transects it varied from 0.29 to 1.0 (Table 25). Transect wise dominance recorded in 

! 

, JilTcrent depth zones showed that (Fig. 46) at 30 m depth zone, fluctuating trend was 

observed with maximum dominance off Mumbai and minimum off Ratnagiri. At 50 

m depth zone also, fluctuating trend was observed with high dominance observed off 

\1orrnugao and Dwaraka and low off Ratnagiri. In both these depth zones (30 m and 

I )0 m), minimum dominance was observed off Ratnagiri. At 75 m depth zone, 

dominance was fluctuating. It increased up to off Mumbai then decreased to off 

Dwaraka. Minimum value was observed off Dwaraka and maximum value off 

Mumbai. At 100 m depth zone, southern latitude stations of Mormugao and Ratnagiri 

noticed higher dominance and rest of transects have low dominance. Highest 

dominance was observed off Mormugao and lowest off Mumbai. At 150 m depth 

lone, only three observations were made and no regular trend was observed with 

highest dominance off Dwaraka and lowest off Veraval. At > 150 m depth zone, no 

comparison was possible due to reduced number of observations. Generally no 

regular transect wise trend was observed for dominance. 


The composition of Macrobenthos showed that during both seasons 

polychaetes were dominated with 86% during post-monsoon and 80% during pre 

monsoon. Crustaceans increased from post-monsoon (4%) to pre- monsoon (6%), 

molluscs decreased from 8% to 5% during the post-monsoon and pre- monsoon 

seasons respectively. The miscellaneous group showed a drastic change between the 

two seasons, during post-monsoon it was 0.7% and increased to 8% during pre 

monsoon. Generally during post-monsoon, groups/species were low in all the depth 

150

Table 17. contd .. 

._---_. 

P.ehlersi 20 60 0 33 0 

P.cirr!fera 60 100 100 50 0 

PYKospio elegans 0 0 0 33 0 

Spiophanes kroyeri 0 0 20 0 0 

S. bombyx 0 0 0 17 0 

Malacoceros indicus 0 0 60 17 0 

Spionid sp. 0 0 20 0 0 

Magelonidae 0 0 0 0 0 

Magelona cincta 60 40 60 17 0 

Mcapensis 80 60 40 33 0 

Cirratulidae 0 0 0 0 0 

Cirralulis cirratus 80 80 60 67 0 

Cbioculalus 0 20 0 0 0 

C.Kilchrisl 0 20 0 0 0 

Cchrysoderma 20 20 40 17 33 

C.concinnus 0 0 0 0 0 

Cirr!formia afer 20 40 40 17 0 

Tharyx dorsobranchialis 0 20 40 0 0 

Disomidae 0 0 0 0 0 

Disoma sp. 0 0 20 0 0 

Orbiniidae 0 0 0 0 0 

Scolaricia dubia 20 0 60 0 0 

Schroederella pauliani 20 0 20 0 0 

Paraonidae 0 0 0 0 0 

Paraonides lyracapensis 0 20 40 0 0 

P./yra/yra 40 20 20 0 33 

Paraonis gracilis gracilis 0 0 40 0 0 

Aricidea capensis 20 20 20 17 0 

A.fauveli 40 0 0 0 0 

Cossuridae 0 0 0 0 0 

Cossura coasla 100 80 80 17 67 

Capitellidae 0 0 0 0 0 

Capitella capitata 100 80 40 50 0 

Heleromastides bifidus 60 0 20 0 0 

Nolomastus aberans 20 0 20 0 0 

N.fauvelli 40 0 20 0 0 

Paraheleromastes tenuis 20 60 20 33 0 

Heleromaslus fili/ormis 20 0 0 0 0 

Mediomastes capensis 20 0 20 0 0 

Maldanidae 0 0 0 0 0 

Ma/dane sarsi 40 20 20 17 0 

Ma/denella capensis 40 0 0 0 0 

Axiolhella jarli 0 0 20 0 0 

Ma/dane sp. 0 0 0 0 0 

166

Tablc 17. Contd .. 

- Sternaspidae 0 0 0 0 0 

Sleraspis seutata 40 60 20 17 0 

FlabeJligeridae 0 0 0 0 0 

Pycnoderma eongoense 0 0 40 0 0 

Ampharetidae 0 0 0 0 0 

Amphrete aeutifrons 20 20 0 0 0 

Amphicteis gunneri 0 20 20 0 0 

Amphicteis sp. 0 0 0 0 0 

Phyllocomus hi/toni 20 0 0 0 0 

Terebellidae 0 0 0 0 0 

Terebellides stroemi 20 0 20 0 0 

Lanice conchilega 0 0 20 0 0 

Slreblosoma persiea 0 0 20 0 0 

Lysilla sp. 0 0 20 0 0 

Pisla foliigera 0 0 20 0 0 

P.quadrilobata 0 0 20 0 0 

Arlacama proboscidea 20 0 0 0 0 

Sabellidae 0 0 0 0 0 

Megalomma vesieulosum 0 0 40 0 0 

Desdemona ornata 0 0 20 0 0 

Total species 37 34 59 27 6 

Errantia 8 11 19 8 1 

Sedentaria 29 23 40 19 5 

Abundant species 6 7 4 1 0 

Moderately occurring species 12 10 18 10 6 

Rare species 19 17 37 16 0 

167

Taxa 30m 50m 75m lOO m 150m 

CRUSTACEANS 

Oecapoda sp. 80 20 0 33 

Scrgestid 20 0 0 17 

Megalopa 60 0 0 17 

Lobster 20 20 0 33 

Caridian prawns 80 20 60 17 

Acetes 0 0 0 17 

Amphipoda 0 0 0 0 

Melila zeylanica 0 0 0 17 

Eriopisa chi/kensis 40 20 20 0 

Quadriovisio bengalensis 20 20 0 0 

Grandidierella gilesi 40 0 20 0 

Isopoda 0 0 0 0 

Anthuridae 20 0 20 0 

Ostracoda 20 20 0 0 

-- 

MOLLUSCS 0 0 0 0 

Cardium sp. 20 20 0 33 

Bivave 0 0 0 0 

Mactra sp. 40 20 20 33 

Tellina sp. 20 60 0 17 

Si/iqua sp. 0 0 0 17 

Sunetla scripta 0 0 20 17 

Gastrpod 0 0 0 0 

Nassarius sp. 40 0 20 17 

Prunum sp. 0 0 0 17 

Bulla sp. 0 0 0 17 

Atys sp. 0 20 0 0 

_._-- 

MISCELLANEOUS GROUPS 0 0 0 0 

Nematodes 20 0 0 0 

Sipunculoides 60 20 20 0 

Juvenile fish 0 20 0 0 

Platyhelminthes 20 20 0 0 

Nudibranches 0 20 0 0 

Echiroides 20 0 0 0 

Total groups 18 14 8 15 

Abundant species 2 0 0 0 

Moderately abundant species 6 I 1 4 

Rare s(!ecies 10 13 7 11 

Table 18 - Percentage occurrence of groups in various depth zones during postmonsoon 

0 

0 

0 

() 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

33 

0 

67 

100 

0 

33 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

4 

1 

3 

0 

168

Table 20. contd .. 

G. alba 20 25 20 20 33 0 

Gonioda emerata 40 25 60 20 0 0 

[unicidae 

LlImbriconeries aberrans 20 75 20 40 0 0 

L. hartmani 80 50 60 40 33 0 

L.laterali 0 25 20 20 0 0 

LlImbrineries sp. 40 0 20 0 0 0 

E. indica 0 0 0 0 33 0 

Eunice sp. 0 0 20 0 0 0 

ElIniphis emerita 0 0 20 0 0 0 

Protodorvillea biarticulata 0 0 20 20 0 0 

Diapatra sp. 0 25 20 0 0 0 

Diopatra monroi 0 0 20 0 0 0 

Diopatra neopolitana 0 25 0 0 0 0 

Epidiopatra sp. 0 0 0 20 0 0 

Ophryotrocha puerilis 0 0 0 20 0 0 

Dorivilla gardineri 0 25 20 20 0 0 

Dorivilla sp. 0 0 20 0 33 0 

SEDENTARIA 

Spionidae 

Prinospio pinnata 100 75 100 100 67 0 

P.polybranchiata 80 75 60 20 33 0 

P. cirrobranchia 60 50 80 60 0 50 

P. sexoculata 0 25 0 0 0 0 

P.chelersi 0 0 20 20 0 0 

P.cirrifera 60 50 80 80 0 50 

Prinospio sp. 40 0 0 0 0 0 

Pygospio elegans 0 0 20 20 33 0 

Spiophane bombyx 0 0 40 20 33 0 

.\falacocirus indicus 0 0 40 0 0 0 

Bocardia sp. 20 0 0 0 0 0 

Scolelepis sp. 0 25 0 20 0 0 

Magelonidae 

.lfagelona cincta 60 50 80 80 67 50 

.If. capensis 20 0 20 0 0 0 

.'v/agelona papilicornis 0 0 20 0 0 0 

Cirratulidae 

Cirratulis cirratus 20 50 80 80 67 50 

Cchrysoderma 0 25 40 0 0 0 

Cauleriella capensis 0 25 0 0 0 0 

Cirriformia a/er 60 50 100 60 33 0 

Tharyx dorsobranchialis 0 25 0 0 0 0 

T fllibranchia 0 25 0 0 0 0 

Tharyx sp. 20 0 40 80 33 0 

171

Table 20. Contd .. 

Pectinariidae 

--------------- 

Peclinaria capensis 20 0 0 0 0 0 

Peclinaria sp. 

Ampharetidea 

40 25 0 20 33 0 

Isolda whydahensis 0 0 0 0 33 0 

Ampharete agulhasensis 0 25 0 20 0 0 

Amphicleis gunneri 40 50 80 100 67 50 

."iabellides luderitzi 0 0 20 0 0 0 

Sabellides capensis 

T erebellidae 

0 0 0 0 33 0 

Polycirrus haematodes 0 25 0 0 0 0 

P. coccinius 0 0 20 0 0 0 

Polycirus sp. 0 25 20 0 0 0 

Terebellides stroemi 40 25 0 0 0 0 

Slroblosoma persica 0 0 0 20 0 0 

Lysilla ubiansis 20 0 0 0 0 0 

P. brevi branchia 0 0 20 0 0 0 

Telolhelepus capensis 

Sabellidae 

0 0 0 0 0 50 

Ellchone rosea 0 0 20 0 0 0 

.\legalomma vesiculosum 0 0 20 20 0 0 

."iabellid sp. 0 0 20 0 0 0 

Amphiglena mediterranea 0 0 0 0 0 50 

[hone collaris 0 0 20 20 0 0 

C lellerstedti 0 0 0 20 33 0 

Oriopsis eimeri 0 0 0 0 33 0 

Fabricia jiJamentosa 0 0 0 0 33 0 

Serpulidae 20 0 0 0 0 0 

Prolula tubularia 0 0 20 0 0 0 

Serpu/id sp. 0 0 0 20 0 0 

I'ermiliopsis acanthophora 0 0 0 20 0 0 

Polygordius 0 0 0 20 0 0 

T Dial species 52 58 72 66 39 15 

[mntia 12 18 26 24 12 4 

Sedentaria 40 40 46 42 27 11 

Abundant species 6 8 10 9 1 0 

\toderately abundant species 21 50 18 9 38 15 

Rare species 25 0 44 48 0 0 

173

150 

Taxa 30m 50m 75m lOOm 150 m m 

Decapoda 40 25 80 100 100 0 

Sergestid 0 0 0 0 33 0 

Megalopa 20 0 0 20 67 0 

Crab 0 50 0 0 0 0 

Alima larvae 0 0 20 0 0 0 

Juvenile Lobster 0 0 40 0 33 0 

Amphipoda 0 0 0 0 0 0 

Corophium triaenonyx 0 0 0 20 0 0 

Caprillidae( amphi pod) 0 0 0 20 0 0 

Melita zeylanica 0 0 20 0 0 0 

Eriopisa chilkensis 

60 75 80 40 67 50 

Quadriovisio bengalensis 40 0 40 40 0 0 

Grandidierella gilesi 

20 25 60 80 33 0 

G.gonneri 0 0 20 20 33 0 

lsopoda 0 0 0 20 0 0 

Cirrolinea fluviata 0 0 0 20 33 50 

Anthuridaea sp. 20 25 60 20 33 0 

Cumacea 40 25 20 0 33 50 

Mysid 0 0 20 0 0 0 

Tanais sp. 0 0 40 40 0 0 

Apsudus chilkiensis (tanaidacaea) 20 0 20 40 33 0 

Mollusca 0 0 0 0 0 0 

Patella sp. 0 0 20 0 33 0 

Nucula sp. 0 0 0 0 33 0 

Sunetta scripta 0 0 60 20 0 0 

Mactra sp. 40 50 40 40 33 0 

Glycimeris sp. 0 0 40 20 0 0 

Tellina sp. 0 50 40 20 33 0 

Siliqua sp. 20 0 0 0 0 0 

Solen sp. 0 0 0 40 0 0 

Littorina sp. 40 0 20 40 0 0 

Prunum sp. 20 0 20 40 0 0 

Nerita sp. 0 0 0 40 0 0 

Nassarius sp. 60 25 20 80 33 0 

Bulla sp. 0 0 20 40 0 0 

Turritella sp. 0 0 0 20 0 0 

Terebra sp. 0 25 20 40 0 0 

Atys sp. 0 0 0 60 33 0 

Oliva sp. 0 0 0 20 0 0 

Cerithidea sp. 0 0 0 20 0 0 

Table 21. Percentage occurrenl:e of groups in various depth zones during 

pre-monsoon season. 

174

Depths Margalef Evenness Shanon Simpson 

index index index index 

30m 1.4831 (8) 2.4089 (8) 2.3916 (8) 2.2907 (8) 

SOm 1.5034 (7) 0.6178 (7) 1.6897 (7) 1.5863 (7) 

75m 0.4284 (8) 3.0785 (8) 0.1245 (8) 0.7493 (8) 

lOOm 2.8138 (8) 3.6274 (8) 1.5463 (8) 0.8343 (8) 

150 m 1.5012 (6) 0.9519 (6) 1.0985 (6) 0.6159 (6) 

Table 26a - Seasonal comparison of community structure indices of polychaete 

Species based on Student's t test (Degree of freedom is given in bracket) 

Depths Margalef Evenness Shanon Simpson index 

index index index 

30m 1.3581 (8) 3.0721 (8) 3.7718 (8) 3.1257(8) 

50m 0.9595 (7) 0.3133 (7) 0.6162 (7) 0.4465 (7) 

75m 5.6884 (8) 0.1873 (8) 1.7622 (8) 1.0590 (8) 

lOOm 4.6840 (8) 1.1185 (8) 2.5318 (8) 1.4980 (8) 

150 m 2.2399 (6) 0.1060 (6) 1.4810 (6) 1.1192 (6) 

Table 26b - Seasonal comparison of community structure indices of groups based on 

Student's t test (Degree of freedom is given in bracket) 

180

9% 1% 

o poIychaete 

• crustacea 

o mollusc 

• others 

Fig 35 - Fauna} composition (%) during post-monsoon 

o polychaete 

• crustacea 

Cmollusc 

[lothers 

Fig 36 - Fauna} composition (%) during pre-monsoon 

181

'" 

" 

'H 

:0:0."':01 1 

I 

L-_ _ __________ .. ___ __ . __ ! 

Fig. 51 - Dcndrogram (MDS) for stations based on pulychacte density during premonsoon 

season 

'" 

------ -- -- ---.. --- - . -- -;;;-n7il 

I 

I I 

, i 

, 

L. ___________ . _ ___ .. _________ .. ___ ____ J 

Fig. 52 - Dendrogram (MDS) for stations ba

a) 

c) 

e) 

g) 

Plate 5 a) Prinospio sp. 

e) Diopatra sp. 

b) 

d) 

f) 

h) 

b) Capitella sp. c) Syllis sp. 

f) Cirratulus sp. g) Glycera sp. 

d) Cossura sp. 

h) Nephtys sp.

a) b) 

c) d) 

e ) f) 

g) h) 

Plate 6 a) Magelona sp. b) Arenicola sp. c) Sabella sp. d) Sabella sp. 

e) Serpu/a sp. f) Serpu/a sp. g) Serpula sp. h) Serpufa sp.

a) 

c) 

e) 

Plate 7 a) Cardium sp. 

d) Mactra sp. 

b) 

d) 

b) Cardium sp c) Tellina sp. 

e) Prunum sp. f) Prunum sp. 

f)

a) 

c) 

e) 

Plate 8 a) Atys sp. 

d) Grandidiere/fa sp. 

b) 

d) 

b) Bulla sp. 

e) Sipunculid 

f) 

c) Nudibranch 

f) Nematod

7/. /ntroduct ion 

7.2. Hydrography 

7.2.1. Temperature 

7.2.2. Salinity 

7.2.3. Dissolved oxygen 

7.3. Sediment lexture 


7.5. Multiple regression analysis 

7.5.1. Macrohenlhic hiomass 

7.5.2. Macrobenthic density 

7.6. Trophic relationships 



Chapter 7. 

Ecological relationships 

Abundance and diversity of benthic organIsms are controlled by varIOUS 

environmental parameters such as temperature. salinity, DO. OM and sediment 

texture. Depending upon the habitat and the community inhabits, the intensity in the 

influence of these factors also varies. All factors have a positive correlation at its 

oplimum levels and influence negatively beyond this limit and this optimum limit 

varies with organisms. Based on the habitat. like intertidal zone, littoral and deep 

sea, organIsms develop many adaptations to cope up with the environmental 

conditions. 

Arabian sea IS UnIque for its seasonally oscillating monsoon system and 

associated features (Qasim, 1982). Northern Arabian Sea is peculiar in its negative 

water balance, which result in the formation of several low and high water masses 

)96

(Gupta and Naqvi, 1984). It is also a unique feature in its land locked boundary in the 

north and predominant oxygen minimum zone prevailing in that area. All these have 

an effect on the benthic community and previous studies in the estuarine and coastal 

waters have shown the effect of various environmental factors on benthic distribution 

(Varshney et al., 1988; Harkantra and Parulekar, 1991&1994; Ansari et al., 1994; 

Harkantra and Rodrigues, 2003) and the destruction of benthic fauna associated with 

fresh water influx during monsoon and their re-colonization (Hark antra and 

Parulekar, 1981, Vizakatetal., 1991). 

7.2. Hydrography 

7.2.1. Temperature 

From the hydrographic data a decrease in temperature with increase in depth 

and also a northward increase was evident during post-monsoon. Similar to the 

distribution of temperature, total benthic biomass also showed a decrease towards 

deeper depth zones during post-monsoon, which clearly indicated the influence of 

temperature on benthic production. Similar to the total biomass, biomasses of 

polychaetes and miscellaneous groups also decreased with depth. Molluscs showed 

comparatively high values at 30 m and 50 m while crustaceans were abundant at 30 

and 50 m with some exceptionally high values at deeper depths (lOO m). Results 

revealed that temperature appears to influence the entire benthic community. 

Correlation analysis (Table 27) showed a positive relation of total biomass (r=0.600, 

p

also showed a similar pattern with salinity distribution. Miscellaneous groups showed 

a more or lcss similar pattern with salinity in the northern and southern transects. But 

crustaceans and molluscs were more in deeper stations. Correlation analysis (Table 

27) showed positive correlation with total biomass, biomass of polychaetes, 

crustaceans and miscellaneous groups and negative correlation with molluscs. 

Latitudinally, salinity showed an increase towards north in most of the depth zones 

during both seasons and benthic biomass was also more in the northern stations 

during both seasons. This may be due to the influence of salinity on benthic 

production. Comparatively high salinity was observed during pre-monsoon, which 

corroborates with the high biomass in that season. During post-m on soon polychaete 

density and total density was negatively correlated with salinity (Table 28), but 

density of crustaceans, molluscs and miscellaneous groups showed positive 

correlation with salinity of which the relation with molluscs is at significant level 

(F0.505. p

Many workers have suggested that salinity had a strong relation with benthos. 

lIarkantra and Parulckar (1991), Vizakat et al.,(l99l) and Harkantra and Parulckar 

(1994) reported decreased population of benthos during monsoon months and its 

recolonisation after the monsoon indicated the role of salinity in benthic production. 

Ingole and Parulekar (1998) stated that salinity could act as a community regulator 

determining the physiological activity of marine organisms. They observed two 

maxima in faunal abundance first in December and second in March. This agrees 

with the present study as high benthic biomass was observed during pre-monsoon 

and it might be due to the second recolonisation after the post-monsoon season with 

increasing salinity as observed by the above authors along with other ecological 

parameters. Temperature and salinity of the sea water were regarded as important 

regulators of the reproductive cycle of marine invertebrates (Kinne, 1977; lngole and 

Parulekar, 1998) and those marine species inhabiting the tropical region generally 

have very narrow range of temperature tolerance since they normally live in a 

temperature regime that is closer to their upper tolerance limit. Therefore important 

variables controlling the distribution and abundance of benthic organisms in the 

tropical regime were salinity (Parulekar and Dwivedi, 1974; Alongi, 1990;) and 

sediment stability (Wildish and Kristmanson, 1979; Warwick and Uncles, 1980). 

7.2.3. Dissolved oxygen (DO) 

During both seasons DO decreased towards deeper depths and showed anoxic 

condition especially in the northern transect. In shallow depth zones, DO was low in 

southern transect and comparatively high in the northern transect. Increasing trend of 

biomass towards north showed positive correlation with high DO in the north. But in 

the deeper depths (beyond 100 m) DO drastically reduced and northern latitude 

stations recorded very low values. The lowest biomass was also observed in the 

deeper depths (beyond 100 m) during both seasons. This could be due to the 

anaerobic or suboxic condition prevailing in that region which could not be tolerated 

201

y most of the organisms. It was also noted in the present study that, DO was 

comparatively high during pre-monsoon and low during post-monsoon. This high 

DO value during pre-monsoon might also have positively influenced high benthic 

biomass in this season when compared to post-monsoon. Correlation analysis showed 

that (Table 27), during post-monsoon, total biomass and biomass of polychaetes, 

molluscs and miscellaneous groups were positively correlated with DO while 

crustaceans were negatively correlated. During pre-monsoon, total biomass and 

biomass of polychaetes and miscellaneous groups were positively correlated with DO 

whereas crustaceans and molluscs were negatively correlated. For density, 

correlation analysis showed that (table 28) all benthic groups were positively 

correlated with DO except molluscs during post-monsoon season, and the relation 

between crustaceans were at significant level (r=0.423, p

Decrease of benthos with DO agrees with earlier reports. Neyman (1969) 

noticed a decline in benthic organisms in the northern shelf of west coast of India at 

the depth of 75 to 200 m and this was attributed to the impact of reduced DO. 

Parulekar and Ansari (1981) pointed out that low levels of DO especially below 200 

m depth in the Andaman waters resulted in low macrobenthic biomass. Rosenberg 

(1977) reported that low oxygen content causes high physiological stress resulting in 

considerable impoverishment in the benthic production. Joydas (2002) recorded near 

anoxic values in the depth > 150 m in the northern shelf edge of Arabian Sea 

characterized by low biomass, density, species richness and diversity which also 

agrees with present observation. 

7.3. Sediment Texture 

The results of the sediment analysis showed that clay content predominated in 

the shallow depths and sand in the deeper depths during both the seasons. Moreover, 

southern transects recorded sand dominated sediment and northern transects were 

dominated by fine sediment. Total biomass and biomass of polychaetes, molluscs and 

miscellaneous groups were high in shallow depths and low in deeper depths thus 

showing the influence of fine texture. Biomass of crustaceans was higher in deeper 

depths showing the influence of the sand dominating texture. Correlation analysis 

showed that (Table 27) during post-monsoon, total biomass (r= -0.515, p

with sand of which total density (r=-0.499, p

crustaceans. This indicated that during post-m on soon most of the groups were 

positively correlated with fine sediment and negatively correlated with sand except 

for crustaceans. The fuanal distribution with respect to texture also (Table 29) 

showed that during post-monsoon polychaetes was abundant in the silty clay and 

clayey sediment while crustaceans were more in silty clay and clayey sand. Molluscs 

preferred silty clay substratum and miscellaneous groups were present only in silty 

clay and clayey sediment. Thus during post-monsoon most of the benthic groups 

preferred fine sediment texture with low sand content. This was evident from the 

decrease of biomass of all benthic groups with the increase in sand except the 

crustaceans. During pre-monsoon, sand prevailed in the deeper depths and clay 

content was more in the shallow depths. The abundance of Polychaetes and 

miscellaneous groups in the shallow depths indicated their affinity to the fine 

sediment and abundance of crustaceans and molluscs in the deeper stations clearly 

indicated a positive correlation with sand content. The faunal distribution with 

respect to different texture also (Table 29) showed that during pre-monsoon, 

polychaetes preferred fine sediment texture with a mixture of sand and clay. 

Crustaceans dominated in sandy sediment while molluscs were abundant in the 

clayey sand and the sandy sediment. This showed the preference of crustaceans and 

molluscs to the sand dominated sediment. 

Results showed that total biomass and biomass of polychaetes and 

miscellaneous groups were positively correlated with fine sediment and that of 

crustaceans with coarser fraction. Molluscs prefer sand or a mixture of sand and mud. 

From statistical analysis (Table 27 &28) it was clear that most of the benthic groups 

were influenced by sediment texture in their distribution even though it was not at a 

significant level. So it can be stated that sediment texture is not the single controlling 

factor, texyure together with other ecological factors controls the benthic distribution. 

Earlier works also reported the preference of benthos to the substrata. Neyman 

(1969) observed that polychaetes, bivalves and echiuroidea were abundant in the 

205

muddy bottom of the west coast of India. Ansari et al., (1977) stated that polychaetes 

prefer muddy sand and were completely absent in the clayey sediment. Pelecypods 

prefer fine sediment with high percentage of silt and clay and they have also noticed 

that amphipods depend on the availability of OM rather than the type of sediment. 

Savich (1972) also observed the dependence of benthos to the substratum. Parulekar 

and Wagh (1975) studied the benthos of northeastern Arabian shelf and suggested 

that bottom deposits of sand with a mixture of clay or silt form an ideal substrate for 

polychaetes and bivalves. They also inferred that substratum, along with OM act as 

an important ecological factor in the distribution of bottom fauna along the north 

west coast of India. Eggleton (1931) found complete absence of bottom animals on a 

substratum of clean sand, but he added that a dense population could exist if there is 

a strong current bringing in nutrients or the productivity of the water column above is 

high. Panikkar and Aiyar (1937) observed the absence of animals on substrata of 

thick clay and their abundance on loose substratum. Kurian (1967) observed that 

sandy deposits had high abundance of benthos at some places while in others, 

production was low in similar deposits and suggested that type of substratum cannot 

be considered independently as a major ecological factor determining the distribution 

and abundance of bottom fauna. Harkantra et al., (1982) found the dominance of 

polychaetes in the silty sand and low in the clayey sediment while bivalves were 

more in the sandy clay and suggested that seston feeding animals were mainly 

restricted to sandy areas with low percentage of silt and clay whereas detritus feeders 

and deposit feeders were restricted to muddy areas. A specificity of faunal density to 

the type of substratum largely depends on feeding habits. Presumably fine particles 

of clay results in the clogging of filter feeding apparatus of the filter feeders hence its 

avoidance from inhabiting the fine particle size substrata. 

Sanders (1968) and Boesch (1973) suggested that in a given geographical 

area, sandy substratum harbour high standing stock of benthic fauna besides 

supporting a more diversified community than muddy sediment. Devassy et al., 

206

(1987) also found high population density in the shallow areas where the texture was 

sandy and low density in higher depths where the texture was muddy in nature. 

Ingolc et al., (1992) reported that variation in benthic standing crop might be due to 

the changes in sediment texture and variation in depth. Thomas (1970) stressed the 

importance of substratum in controlling the abundance of marine organisms and 

statcd that the abundance of sediment covering coarser bottom has pronounced effect 

on benthic biota. Ansari et al., (1994) reported that the sandy sediments support high 

biomass and Ingole et al., (2002) noticed that medium sand grain size support a good 

bcnthic crop. From the present study and the earlier reports it can be stated that type 

of substrata influences benthic abundance and distribution. 

7.4. Organic matter (OM) 

In the study area OM was generally high in the shallow depths (30m and 50 

m) and low beyond 50 m with some exceptions especially in the northern transects 

during both the seasons. During post-monsoon, total biomass and biomass of 

polychaetes, molluscs and miscellaneous groups were more in lower depths (up to 50 

m) while crustaceans were more in shallow depths (30 m and 50 m) with some 

exceptions in deeper depths. Correlation analysis (Table 27) showed that during post 

monsoon season total biomass, biomass of polychaetes, and miscellaneous groups 

wcre negatively correlated with OM while crustaceans and molluscs were positively 

correlated, of which relationship of molluscs was at a significant level (r=0.457, 

p

crustaceans and miscellaneous groups were negatively correlated while during pre 

monsoon, all the faunal groups were negatively correlated (Table 28). 

Effect of OM on the community structure of polychaetes and all the groups 

combined during post-m on soon and pre-monsoon season respectively is given in Fig. 

67 and 68. During post-monsoon, species richness, evenness and diversity were 

negatively correlated with OM while dominance was positively correlated (Fig. 67 a 

d). Community structure based on groups (Fig. 67 e-h) showed a positive correlation 

for richness, evenness and diversity with OM but negatively correlated with 

dominance. During pre-monsoon, richness, evenness and diversity were negatively 

correlated while dominance was positively correlated with OM (Fig. 68 a-d). 

Community structure based on groups (Fig. 67 e-h) showed a negative correlation 

with richness and diversity but not much con troll on evenness and dominance. 

In general no consistent relationship with OM was observed, however benthos 

were usually low in places with very high OM (>3%). The relationship between 

bcnthic abundance and percentage of OM has been studied by many workers (Bader, 

1954; Sanders, 1968; Ganapati and Raman, 1973). Sanders et al., (1965), Varshney et 

al., (1988) and Joydas (2002) could not observe any consistent relationship between 

OM and faunal abundance. Bader (1954) while studying the abundance of bivalves in 

relation to percentage of organic carbon observed a decrease in population when the 

OM was more than 3%, which is comparable with the present study. He pointed out 

that beyond this concentration, products of bacterial decomposition and decline in the 

available oxygen become the limiting factors. Harkantra et al., (1980) observed that 

organic carbon was related to the textural characteristics of the sediment and also 

observed a decrease in benthic animals when the OM was high (>4%). Hence OM 

seems to be one of the limiting factors controlling the distribution and abundance of 

benthic population. Ganapati and Raman (1973) who studied the pollution in 

Visakapatnam harbour found that discharge of domestic waste into the harbour 

waters led to the anoxic condition, which adversely affected the organisms. This is 

208

uue to the accumulation of OM (6%) in the substrate and emanation of lhS, resulting 

anoxic condition to the marine life. Parulekar and Wagh (1975) stated that suspended 

OM and substratum act as important ecological factors controlling the distribution of 

benthos along the northeastern Arabian shelf. Vizakat et al., (1991) observed the role 

of OM of the sediment as one of the factors controlling the distribution and 

abundance of sediment dwelling benthic fauna. Prabhu et al., (1993) showed a direct 

relationship of echiurids and polychaetes with the amount of OM while Ansari et al., 

(1994) opined that moderate organic enrichment has a biostimulating effect on 

benthic community and high organic enrichment will lead to eutrophication and 

unsuitable environment conditions for the benthic life. Gopalakrishnan and Nair 

(1998) also reported that slightly higher OM (1.97%) enhanced the benthic 

production. Kumar and Antony (1994) studied the impact of environmental 

parameters on polyehaetes in the mangrove swamps of Cochin and noticed no direct 

correlation between polychaete fauna and OM. From the present study it can be 

stated that benthos were not significantly related to OM but get adversely affected if 

it goes beyond a level (3%). 

Most of the polychaete families had their representation in the shallow depths 

and got reduced below 100 m. Sedentarians were more in all depths than errantia 

during both the seasons showing their ability to withstand the adverse conditions. All 

the families showed more occurrences in the shallow and middle depths especially at 

75 m when compared to other depths. Below 75 m depth, spionids, cirratulids, 

eunicids and glycirids showed better occurrence. Beyond 100 m spionids, cossurids 

and cirratulids are the only representatives. In errantia pilargids alone were found at 

150 m depth zone. During pre-monsoon among sedentarians, spionids and capitillids 

were high in occurrence in the> 150 m zone than other groups. 

High representation of spionids and capitellids at all depths may be due to 

their ability to withstand adverse environmental conditions. It is well established that 

capitillids are used as indicators of organic pollution owing to their ability to live in 

209

the organic rich environment with high OM. The present study also confinns the 

above fact. Joydas (2002) observed the dominance of spionids and cirratulids in the 

low oxygen environments. Ingole et al., (2002) noticed the dominance of spionids in 

the coastal waters of Dabhol, west coast of India. Among spionids, Prinospio pinnata 

was the most abundant species. The abundance of spionids in the deeper depths 

showed that these organisms have a low metabolic rate and can withstand adverse 

conditions. The decrease in temperature with increase in depth supports the above 

statement. 

7.5. Multiple regression analysis 

Step up predictive multiple regression model for biomass and density of 

polychaetes, crustaceans, molluscs, miscellaneous groups and total benthos from the 

environmental factors during post-monsoon and pre-monsoon season was carried 

out. 

A total of 8 parameters were measured among which a set of highly 

correlated 6 factors were selected during post-m on soon and pre-monsoon season as 

the input variables along with their first order interaction effects. This model selects 

the one, which could explain the maximum variability from a set of 64 models for 

each of the three transfonnations viz, 

1. original values of densitylbiomass on original values of the input 

factors 

2. original values of density/biomass on log 10 of input factors 

3. log 10 of density/biomass on log 10 of input factors 

In each case, the factors were standardized to standard nonnal variables as 

y-y x-x 

210

important parameters were graded as OM, saliniy, OM*temperature, temperatue, 

OM*salinity and temperature*saliniy. This model could explains only 31 % of the 

variaions in the spatial distribution of the mollusc bomass at 5% significance level 

(p

Icvci (p

Macrobenthos, by feeding on meiobenthos and OM. and fonning food for higher 

fonns like fishes remain an important component of the food wcb. Among the 

bcnthic animals, polychaetes are the principal components (Longhrust and Pauly, 

1987). Benthic organisms, which inhabit the bottom of the sea largely, fonn the food 

for the most of the commercially important bottom dwelling finfishes and shellfishes 

(Savich, 1972). Hence their prey-predator relationship, benthic biomass and its 

production data help in the estimation of demersal fishery resources based on the 

hypothetical food pyramid or bioenergy flow (Odum, 1973). The standing crop of 

macrobenthos is not only important to the demersal fishes which directly feed on 

them, but also to many pelagic species that are restricted to shallow waters during 

some period of their life (Kurian, 1971). So estimation of benthic standing crop 

production is necessary for the assessment of demersal fishery (Damodaran, 1973, 

Harkantra et al., 1980). An analysis of benthic biomass distribution and demersal fish 

catch showed a positive correlation as areas with high benthic biomass were found 

supporting greater density of bottom fishes (Harkantra et al., 1980). West coast shelf 

region of India showed high demersal fish catch particularly in the near shore region 

0; south west coast which was largely due to the upwelling phenomenon (Warren, 

1992). In addition to their importance in fishery resources, some of the burrowing 

benthic organisms like polychaetes and amphipods are regarded as the efficient 

bioturbators and recyclers of nutrients. 

Meiofauna once thought to be the trophic dead end (Mc Intyre and Murison, 

1973) are now known as an important component in the diets of fish (Bell, 1980; 

Hodson et al., 1981; Coull and Palmer, 1984; Coull et al., 1995; Greg et al., 1998). 

There has been much controversy in the interaction between meiofauna and higher 

trophic levels. Mc1nture and Murisin (1973) and Heip and Smol (1975) suggested 

that primarily meiobenthic predators consume meiobenthic prey species and thus 

were not available to higher trophic levels. Mc1ntyre (1964) and Marshal (1970) 

stated that there is competition for food between macro and meiofauna and that 

21.5

mcioHmna serve primarily as rapid metazoan nutrient regeneration. However, Feller 

and Kaczynski (1975) and Sibert et al., (1977) showed that juveline salmon feed 

almost exclusively on meiobenthic copepods, Odum and Heald (1972) reported that 

meiobenthic copepods comprise 45% of the north American Grey mullot gut 

contents. Sikora (1977) has reported that nematods provide a significant portion of 

the insitu food of the grazing grass shrimp, Palaeomonetcs pugis. Ahlstrom (1968) 

stated that in oceanic stations larvae of Myctophidae and Gonostomatidae dominated 

whereas in the intermediate zone diversified larval forms in large numbers including 

the larvae of several demersal fishes (20%). Mukundan (1971) also reported 

significant number of eggs and larvae from august to December mostly carangids, 

clupeoids and soles. Present study has observed relatively high density and biomass 

of macrobcnthos and meiobenthos during pre-monsoon season than post-monsoon. 

Studies made on fish larvae of the west coast of India by Binu (2003) showed high 

abundance of fish larvae during pre-monsoon season than post-monsoon season. 

Majority of the benthic invertebrates have no direct commercial or recreational value, 

but provides much of the food for bottom feeding species that are themselves 

important in the commercial fisheries of the region. 

According to the present study, the average benthic biomass along the 

northwest coast for the two seasons was 4.16 g/m 2 or 4160 kg/km 2 • Using the 

. 

conversion factor developed by Parulekar et al., (1980), the dry weight for the total 

benthos was 451.12 kg/km 2 and dry weight in terms of carbon (34.5 % of the dry 

weight) was 155.64 kg C/km 2 • Annual production would be twice of the standing 

crop (Sanders, 1956) so it is about 311.28 kg C/km 2 /yr. 

Average meiobenthic biomass for both seasons was 2.88 mg/l0 cm 2 (2880 

kg.lkm2). Assuming that ratio of dry weight to wet weight as 1:4 (Gerlach, 1971, 

Wieser, 1960), the dry weight obtained from wet weight was 720 kg/km 2 and carbon 

content (34.5% of dry weight) will be 248.4 kg C/km 2 • Most of the meiofauna has got 

216

a life span of about 3 months (Sajan, 2003), and then the annual production will be of 

993.6 kg C/km2/yr 

The area covered in the present study is approximately 55000 km 2 . An average 

biomass of 4.16 g/m 2 when converted to annual benthic production (Slobodkin, 

1962) gives a value of 8.32 g/m 2 /y. The benthic production in tenns of wet weight in 

the study area of 55000 km 2 will be 0.46 million tones. Since transfer of energy to the 

next trophic level is approximately 10 %, production transferred to the tertiary level 

will be 0.046 million tonnes. 

Meiobenthic annual production will be 11520 kg/km2 (2880 kg/km2 *4) and 

production from the study area will be 0.6336 million tones. So the total benthic 

production (macro+meio) will be 1.0936 miilion tones. Considering an ecological 

transfer efficiency of 10 %, benthic potential will be 0.10936 million tones. 

According to Somvanshi (1998) present exploitation is 1.875 million tons/y 

along the west coast of India. Assuming that 92.9 % of which is supported by 

continental shelf within 200 m depth zone the production will be 1.75 million tons 

(m. 1.) of which demersal fishery contribute 49% (Sudarsan et aI., 1990). the benthic 

fish production in the continental shelf will be 0.8558 m. t. Considering the area of 

the western continental shelf is 75000 km 2 , which supports 0.8558 m. t. benthic fish 

production, the average demersal fish production in the northwest continental shelf 

will be about 0.5159 m. t. In the present study, annual benthic potential yield is 

0.10936 m t, which can support 21.2% of the current demersal fishery yield of 0.5159 

m t. Limitations of the present study were the sampling was done in the 30-200 m 

and benthic biomass below 30 m depth has not included in the present study. 

Moreover, epifauna and microfuana, which also contributed significant role to 

benthic production, were not taken into consideration. 

Average surface primary production obtained in the near to the coast from the 

two seasons was 20.43 mg C/m3/d and surface chlorophyll a production was 0.64 

mg/m 3 and off coast stations surface primary production was 9.50 mg C/m3/d and 

217

surface chlorophyll a was 0.36mg I m 3 (Madhu, 2005). So annual surface primary 

production will be 745.70 g C/m 3 /y in the near shore region and 346.75 g C/m3/y off 

coast station with an average of 547 g C/m 3 /y in the continental shelf. Considering 

the 20% of the surface production reaches the bottom (Damodaran, 1973), about 109 

g e/m 3 /y is available for benthos. This showed that the primary production of the 

overlying water was not a limiting factor for benthic production. 

218


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224

Polychaetes Crustaceans Molluscs M.G.* Total 

N=23 Post monsoon 

Temperature 0.503* 0.009 0.220 0.452* 0.600* 

Salinity 0.302 -0.361 0.159 0.061 0.261 

DO 0.419* -0.073 0.085 0.042 0.372 

Sand -0.427* 0.066 -0.382 -0.303 -0.515* 

Silt 0.251 0.101 0.118 -0.169 0.194 

Clay 0.397 -0.105 0.388 0.392 0.513* 

OM -0.182 0.039 0.457* -0.056 -0.075 

N=24 Pre-monsoon 

Temperature 0.408* -0.255 0.007 0.005 0.316 

Salinity 0.216 0.165 -0.081 0.315 0.319 

DO 0.363 -0.254 -0.312 0.391 0.394 

Sand -0.142 0.309 0.335 -0.300 -0.161 

Silt -0.026 -0.299 -0.278 0.368 0.054 

Clay 0.287 -0.241 -0.299 0.144 0.236 

OM -0.028 -0.263 -0.039 -0.118 -0.107 

Table 27 - Correlation ofbenthic biomass with environmental parameters during post 

monsoon and pre-monsoon seasons 

(M.G.*- Miscellaneous group) 

Polychaetes Crustaceans Molluscs Others Total 

N=23 Post monsoon 

Temperature 0.492* 0.509* -0.342 0.460* 0.480* 

Salinity -0.207 0.215 0.505* 0.138 -0.140 

DO 0.170 0.423* -0.282 0.324 0.167 

Sand -0.469* -0.325 -0.226 -0.379 -0.499* 

Silt 0.354 0.224 0.317 0.073 0.386 

Clay 0.411 0.291 0.152 0.399 0.435* 

OM 0.103 -0.156 0.235 -0.062 0.113 

N=24 Pre-monsoon 

Temperature 0.429* -0.066 0.331 -0.098 0.397 

Salinity 0.126 0.421 * 0.119 0.314 0.189 

DO 0.170 -0.180 -0.042 0.044 0.141 

Sand 0.179 0.430* 0.305 0.164 0.236 

Silt -0.256 -0.448* -0.248 -0.122 -0.300 

Clay -0.048 -0.299 -0.283 -0.167 -0.103 

OM -0.215 -0.385 -0.033 -0.387 -0.270 

Table 28 - Correlation ofbenthic density with environmental parameters during post 

monsoon and pre-monsoon seasons 

225

Faunal groups Silty Clayey Mixed 

Sand;r sand sand Silty c1a;r Cla;re;r ty(!e 

Post-monsoon 

Polychaetes 140 806 120 1605 1310 100 

Crustaceans 9 40 70 82 34 0 

Molluscs 8 10 10 131 12 20 

Miscellaneous groups 0 0 0 13 18 0 

Total 157 856 200 1831 1374 120 

Pre-monsoon 

Clayey Clayey Sandy Silty Mixed 

Sandy sand silt clay clay type 

Poiychaetes 1692 2763 683 3390 1229 935 

Cru'itaceans 324 110 35 170 140 25 

Molluscs 150 188 75 50 87 125 

Miscellaneous groups 252 112 83 30 196 25 

Total 2418 3173 876 3640 1652 1110 

Table 29. Texture wise distribution of fauna during post and pre-monsoon season 

226

Chapter 8. 

Summary and conclusion 

The benthic organisms play an important role in the marine food chain. The 

demersal fishery potential especially in the coastal waters depends mainly on benthic 

productivity. Small benthic organisms fonn a part of the diet of fishes thus regulating 

the fishery resources of an area. Benthic organisms have been regarded as the best 

indicators of environmental changes caused by pollution, because of their constant 

presence, relatively long life span, sluggish habits and tolerance to differcning stress. 

Since benthic organisms mainly live on the surface of the bottom terrain, are 

influenced by the water column, sediment texture and organic matter. Concentration of 

organic matter also detennines the availability of oxygen. 

Indian ocean has unique features like northern land locked boundary, 

seasonal reversal of monsoonal currents, upwelling and the oxygen minimum layer. All 

these factors may influence the organisms inhabiting the pelagic as well as benthic 

realms. The present study assesses the biomass, density, and community structure of 

benthos in relation to the environmental parameters during post monsoon and pre 

monsoon periods along the northeastern Arabian Sea. Most of the earlier bcnthic 

studies are for localized areas along the west coast extending up to 20 m depth. The 

present study on the macro and meiobenthos from the conticontinental shelf of India 

extending from 30 to 200 m is the first report elucidating the seasonal variations in the 

distribution, abundance and community structure of benthic population. The benthic 

production and abundance had been correlated to the environmental conditions. 

Present study fonns a part of multi disciplinary programme, on Marine 

Research on Living Resources (MR-LR), which includes the assessment of benthic 

productivity of the continental shelf of Indian EEZ. Study area extended from 

245

Mannagoa to Porbandar located between latitude 14° to 22° N and longitude 68° to 

74.5° E and covered an area of - 55000 sq. km. Samples were collected from transects 

off Mannagoa, Ratnagiri, Mumbai, Veraval and Porbander from 30, 50, 75, 100, 150 

and 200 m depths. Water samples for hydrographic parameters were collected using 

Sea-Bird CTD, and sediment samples were collected using Smith-McIntyre Grab. 

Statistical interprettation for community structure was done using PRIMER v 5 

software, and student's t test was worked out for finding the seasonal difference. 

Multiple regression analysis was carried out to find the important ecological factors 

predicting the benthie dictribution and abundance. The fishery potential of the area was 

calculated from the biomass data obtained and compared with the available literature. 

Relationship between macro and meiobenthos was also worked out. 

The thesis is presented in seven chapters. The first chapter gives a general 

introduction regarding the marine environment, its classification, definition, and 

importance of benthos, review of previous works, scope and objectives of the present 

study. 

The second chapter deals with the materials and methods, which covers the 

sampling methods, analytical procedures for the estimation of various parameters, 

collection and processing of benthic organisms and their identification and methods for 

statistical inference. 

The third chapter describes with the general hydrographic features of northeastern 

Arabian Sea. The distribution of environmental features like temperature, salinity and 

dissolved oxygen. During 

Third chapter is on the hydrographic features of the study area and salient 

features are as follows. During post-monsoon, temperature decreased from shallow to 

deeper depths and transect wise analysis showed a general increase towards northern 

stations. During pre-monsoon, temperature initially increased from 30 m to 75 m 

depths and then decreased to deeper stations. It also showed a decrease towards 

northern latitudes. For salinity no consistent depth wise trend was observed during 

l46

zones. Low biomass and density observed at 30 m contour is a peculiarity observed 

during pre-monsoon season. During this season, biomass and density increased from 

30 m to 75 m and then decreased to deeper stations. Biomass was more in the north but 

for density, no general transect wise pattern was observed; however high average 

density was observed in southern transects. Both seasons recorded more or less similar 

biomass with a slight increase during pre-monsoon. Comparatively high density was 

observed during pre-monsoon. Statistical analysis showed no seasonal difference in 

biomass and density between the two seasons. 

Meiobenthic biomass and density decreased to deeper depths. Transect wise 

biomass was more in the northern transect, whereas density showed no regular pattern. 

Nematodes contributed significantly to the total biomass and desity. 

The faunal composition, and the community structure of benthos are presented 

in chapter 6. Four groups viz, polychaetes, crustaceans, molluscs and miscellaneous 

groups were identified from the study area. In polychaetes twenty-four families were 

encountered during post-monsoon and 34 families during pre-monsoon. In both 

seasons sedentarians contributed more than errantia. In errantia, family Pilargidae and 

Eunicidae were the dominant ones during both seasons. In sedentaria, family 

Spionidae and Magelonidae were the major ones during post-monsoon while during 

pre-monsooon family Cirratulidae and Spionidae dominated. Altogether 166 

polychaete species were observed from the study area. Seventy-six species were 

present during post-monsoon, which included 25 errantia species and 51 sedentaria 

species. During pre-monsoon, 133 species were encountered of which errantia 

consisted of 43 species and sedentaria 90 species. During post-monsoon Prionospio 

pinnata was the only abundant species at all depth zones while during pre-monsoon, 

Ancystrosillis constricta and Prionospio pinnata were the abundant species. 

Among non-polychaete taxa, crustaceans were the dominant group mainly 

constituted by decapods during post-monsoon and by amphipods during pre 

monsoon. In molluscs, pelecypods were more frequent during post-monsoon as 

248

against gastropods during pre- monsoon. In miscellaneous groups, sipunculids were 

comparatively high in number during post-monsoon, and during pre- monsoon 

sipunculids and nematods were the major taxa encounterd. Statistical analysis 

showed that species richness was low during post-monsoon. Richness and diversity 

of polychaetes were high in the shallow depths while that of crustaceans and 

molluscs were high in deeper depths in both seasons. 

Trophic relationships showed that primary production was adequate enough in 

the surface layers and was not limiting the benthic production. Estimated fishery 

potential showed that about 21 % of the tertiary production could be supported by 

benthic community (macro and meiobenthos) and rest of which contributed by 

microfauna, epifauna and benthos below 30 m depth. 

13enthic biomass and its relation to the environmental parameters like 

temperature, salinity, DO, sediment texture and OM are discussed in chapter 7. In 

general, benthic biomass was positively related with temperature, salinity and 00. 

Sediment texture was another important factor and polychates and miscellaneous 

groups prefer fine sediment, whereas crustaceans and molluscs prefer sand 

dominated substratum. OM in the range of 1-2% is conducive for benthos beyond 3% 

it adversely affects the organisms. Multiple regression analysis revealed that a 

combined effect of three or more environmental factors affect the biomass and 

density distribution of most of the benthic fauna. But for the density molluscs and 

miscellaneous groups during post- monsoon a minimum of two parameters (viz, sand 

and temperature for molluscs; DO and depth for miscellaneous groups) showed 

higher influence. Thus it can be stated that no single factor could be considered as an 

ecological master factor as observed by Harkantra and Parulekar (1991). Trophic 

relationships showed that estimated annual macrobenthic production for the study 

area is about 311 kgC/km2/yr and meiobenthic production amounts to 994 

kgC/km2/yr (since meiofauna have an average life span of 3 months, total annual 

249

production will be more than that of macrobenthos) and the total annual benthic 

production (both macro and meio) in the study area will be 1.09 million tonnes. 

Average macrobenthic biomass in the study area was 4.16 g/m 2 and for 

meiobenthos it was 2.88 mg/m 2 . Benthic biomass and density was generally high in 

the shallow depths compared to the deeper zone. Average biomass for the shallow 

depths (30 and 50 m) was 6.73 g/m 2 and in deeper depths (150 m and beyond 150 m) 

it was 1.5 g/m 2 . On av average basis, population density for shallow depths and 

deeper depths were 1971 ind/m2 and 790ind/m 2 respectively. Thus a three-fold 

decrease in the benthic biomas and more than one fold decrease in density from 

shallow to deeper depths were observed in the study area. Seasonal difference was 

not observed for biomass as well as density. Latitudinal variation was not well 

defined, however, relatively high biomass was recorded in the northern area while 

density was more in the southern area. Polychaetes were rich and diverse in the 

shallow depths and decreased with depth. in deeper zones, members of family 

Spionidae, Cirratulidae and Cossuridae were predominant suggesting their ability to 

withstand low oxygen conditions. But richness and diversity for crustaceans and 

molluscs were high in deeper depths. Similar to the macrobenthos, total biomass and 

density of meiobenthos were high in shallow depths and low in deeper depths. 

Nematods were the dominant group at all depths and their distribution pattern was 

comparable to that of total biomass and density. Copepods and miscellaneous groups 

were low in shallow depths and high at deeper area. 

Temperature and DO showed significant variations between the seasons but 

significant difference in sediment charecteristics was observed only in the shallow 

depths (30 and 50 m). Benthic biomass and density did not show any significant 

difference for the two seasons. Community structure showed significant changes in 

the two seasons except few depths especially beyond 100 m. Ecological relationship 

showed that combined effects of temperature, DO, salinity and sediment 

charecteristics were mainly steering the benthic production, distribution and seasonal 

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L - Cochin University of Science and Technology

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