Species composition and diversity of free-living Plathelminthes ...

I 

BULLETIN DE L'INSTITUT ROYAL DES SCIENCES NATURELLES DE BELGIQUE 

BULLETIN VAN HET KONINKLIJK BELGISCH INSTITUUT VOOR NATUURWETENSCHAPPEN 

Species composition and diversity of free-living Plathelminthes 

(Turbellaria) from sandy beaches at the Belgian coast 

P. JOUK & E. SCHOCKAERT 

Abstract 

Ten sandy beaches at the Belgian coast were sampled monthly on a 

qualitative basis. Six of them were also sampled quantitatively every 

two months. In total, 130 species were encountered, 38 % of them 

occur only in I or 2 localities, 32 % have a more general distribution (in 

3 to 7 localities) and 30 % are found in at least 8 localities. Schizorhynchia 

generally fonn the dominant taxon in number of species, 

followed by the Proseriata. In Knokke and Het Zwin, equal numbers 

of species were found for both taxa. 

Mariakerke, Bredene, Knokke and Het Zwin have the most diverse 

turbellarian fauna's, with the lowest dominance ratio's. In the semiexposed 

beach of Oostende the fauna is slightly less diverse, dominated 

by a few species, while the sheltered beach in Heist clearly has the least 

diverse fauna, strongly dominated by one species, Archilopsis arenaria. 

Keywords: free-living Plathelminthes, Belgian coast, species richness, 

diversity. 

Samenvatting 

Tien zandstranden aan de Belgische kust werden maandelijks bemonsterd 

op kwalitatieve basis. Zes ervan werden ook tweemaandelijks 

kwantitatief bemonsterd. In totaal werden 130 soorten aangetroffen, 

waarvan 38 % maar in I of 2 localiteiten voorkomen, 32 % een meer 

algemene verspreiding hebben (in 3 tot 7 stranden) en 30 % in minstens 

8 localiteiten aangetroffen worden. Schizorhynchia vonnen doorgaans 

het grootste taxon in aantal soorten, gevolgd door de Proseriata. In 

Knokke en Het Zwin worden gelijkaardige aantallen soorten van beide 

taxa gevonden. 

Mariakerke, Bredene, Knokke en Het Zwin hebben de meest diverse 

turbellariënfauna's, met de laagste dominantie verhoudingen. Het 

semi-geëxposeerde strand van Oostende heeft een iets minder diverse 

fauna, die gedomineerd wordt door enkele soorten. Het beschutte 

strand van Heist heeft duidelijk de minst diverse fauna, die sterk 

gedomineerd wordt door één soort, Archilopsis arenaria. 

Trefwoorden: vrij levende Plathelminthes, Belgische kust, soortenrijkdom, 

diversiteit. 

Introduction 

Free-living Plathelminthes and other soft-bodied meiofaunal 

taxa are often disregarded in biodiversity studies or 

numbers are highly underestimated when they have been 

considered. In most biodiversity surveys, fixed samples 

- - -- --- 

BIOLOGIE, 72-SUPPL.: 35-41, 2002 

BIOLOGIE, 72-SUPPL.: 35-41, 2002 

are used, while the soft-bodied fauna should be studied 

alive to allow proper identification (after which they can 

be recognised in fixed samples). Data on species diversity 

of Plathelminthes are very rare: H' values of 1.20-3.35 

were recorded in beaches of the German Island of Sylt 

(REISE1983a, b, 1984; WEHRENBERG1988) and of 2.55 

maximum in mangrove sandflats of northem Queensland, 

Australia (DlTIMANN1991). MARTENSel al. (1985) and 

MARTENS& SCHOCKAERT (1986) stated that turbellarian 

diversity can be of the same magnitude as that of nematodes 

or harpacticoids, and that turbellarians may represent 

up to more than 25 % ofthe meiofaunal density. The 

data presented here are in the same order of magnitude. 

A general species list of the Belgian coast and adjacent 

areas, listing about 250 species, is given by SCHOCKAERT 

el al. (1990). In this contribution, detailed species lists are 

given for ten sandy beaches at the Belgian coast. Species 

composition, efficiency of specific extraction methods 

for soft-bodied meiofauna and diversity of the turbellarian 

populations are discussed. 

Material and methods 

In ten localities along the 64 km long Belgian coast, live 

samples from the sandy beaches have been investigated 

monthly from April 1985 till June 1986 (see table 2). In 

six of these localities, every two months, 2 cores of 10 cm2 

(40 cm deep) were taken and fixed for quantitative analysis, 

and one for sediment analysis. Samples were taken 

in the medio-litoral zone, where high numbers of individuais 

and of species are to be found (JOUKel al. 1988). 

Living Turbellaria are extracted from the sand by the 

MgClz-decantation method (HULINGS& GRAY 1971, 

MARTENS1984, see SCHOCKAERT 1996), identified under 

the compound microscope and mounted in lactophenol 

for later comparison. Fixed samples are extracted with the 

Bamett-method (BARNETI1968, MARTENS1984), aUflatworms 

mounted in lactophenol and identified.

36 P. lOUK & E. SCHOCKAERT 

Table I - Sedimentcharacteristicsand expositionper locality. 

* Sand: 

Results Species composition 

The /ocalities and the sediment 

The sand become coarser from west to east (see table 1). 

Roughly spoken, there is a gradient in the sediment from 

west to east, with the coarse and less well sorted sand in 

the eastern localities. The most sheltered locality Heist 

however has the finest sand and the highest silt content of 

the ten localities. The relatively sheltered beach of Oostende 

("Klein Strand") has finer sand than the neighbouring 

localities. Except for the two most western (very 

wide) beaches and the most eastern locality, jetties and/or 

piers have been built on the beaches. If sediment characteristics 

reflect the degree of exposure, it can be said 

that Het Zwin and Knokke are the most exposed beaches, 

which can indeed be confinned by (subjective) observation 

of the sites. 

De Panne St.-Idesbald Mariakerke Oostende Bredene 

- mean median 0.200 0.211 0.215 0.208 0.234 

partic1e size (mm) 

- c1assification fine fine fine fine fine 

- sorting very well very well to very well very well very well to 

less well well 

* mean silt % 0.04 0.04 0.01 0.03 0.01 

* mean sand % 098 96.54 96.51 91.56 099 

* mean gravel % 2.45 3.42 3.48 8.39 1.19 

* Sand: 

Blankenberge Zeebrugge Heist Knokke Zwin 

- mean median 0.243 0.226 0.197 0.332 0.316 

partic1e size (mm) 

- c1assification fine fine fine medium medium 

- sorting very well to very well to very well to less well less well 

well well well 

* mean silt % 0 0.02 0.16 0.02 0.02 

* mean sand % 099 099 99.01 97.35 88.57 

* mean gravel % 0.75 0.77 0.84 2.36 11.41 

In total, about 130 species of free-living Plathelminthes 

were encountered (tabie 2). Within the Acoela, only 

Paratomelia rubra was identified to species level. At 

least 15 other species were present, but not identified 

(sectioned material necessary for species identification). 

For the same reason, the three Catenulida-species were 

only identified to family level. 

Based on the live samples, 108 species (Acoela and 

Catenulida not inc1uded) were found throughout the survey. 

Generally, 50 to 60 species were recorded per 10cality. 

In Heist, only 20 species were found. After study 

of the fixed material, only 3 additional species were 

added to the overall list. However, there is a significant 

increase from 10 to 50 % of the number of species per 

locality (table 3): 10-14 % for Mariakerke, Oostende and 

Bredene, 19 and 29 % resp. for Knokke and Het Zwin and 

--- -- -- - - - - - - - -

Species composition and diversity of free-living Plathelminthes (Turbellaria) 37 

Table 2 - Species list per locality. X: present in live samples (10 localities); 0: present in fixed samples (6 localities). 

Acoela 

IJePanne S-Idesbald Mariakm, lmIende BI

38 P. JOUK & E. SCHOCKAERT 

*Kalyptorhynchia 

**Eukalyplorhynchia 

Gnathorbynchidae 

Carcharodagnalhus slilofer (Schilke, 1970) 

X 

Gnalhorhynehus conocaudatus Meixner, 1929 X X XO X X X X XO 

Psillaeorhynehus verweyi den Hartog, 1968 

XO 

UneinorhynehusfIavidus Karling, 1947 

- Cicerinidae 

0 XO 

Cicerina brevieirrus Meixner, 1928 

Cicerina remanei Meixner, 1928 X X XO XO XO x x 

X 

XO 

XO 

XO 

X 

XO 

Cieerina lelradaetyla Giard, 1904 X X X X XO XO 

Paraeieerina delloides Martens & Sehockaert, 1981 X X X XO X XO 

Ptyalorhynehus eaeeus Meixner in Ax, 1951 

- Polyeystidae 

X X 0 XO XO X X XO XO 

Neopolycyslis lridenlala Karting, 1955 X X X X 

Polycyslidarum sp. 

- Cystiplanidae 

X X 

Nigerrhynehus opislhoporus Schilke, 1970 

- Psammorhynehidae 

XO 

Psammorhynehus tubulipenis Meixner, 1938 X X 0 X X X XO XO XO 

- Species incertae eedis 

Elver/ia krusei Noldt, 1989 

**Schizorhyochia 

X 

- Sehizorhynehidae 

Amphirhynehus caudolus Sehilke, 1970 

0 

Carcharodorhynehus isolalus Schilke, 1970 X X XO XO XO X 0 

Careharodorhynehus lislensis Sehilke, 1970 X 0 X 

Limirhynehus danicus Schilke, 1970 X X XO XO XO X X X 

Neosehizorhynehus brevipharynggus Sehilke, 1970 X XO X 0 X X 

Neosehizorhynehus longipharynggus Sehilke, 1970 X X XO XO XO X X X 

Neosehizorhynehus parvoroslro Ax & Heller, 1970 X X XO XO XO X X XO XO 

Neosehizorhynchus sp. X X XO XO XO X X 0 0 

Parasehizorhynehoides glandulis Schi1ke, 1970 X XO 

Prosehizorhynehus bivaginatus Schilke, 1970 X X XO XO X X 0 0 

Prosehizorhynehus helgolandieus I'Hardy, 1965 X X XO 0 XO X X 0 

Prosehizorhynehus gullmarensis Karting, 1950 

XO 

Prosehizorhynchus /TiduelibusSehilke, 1970 X X XO XO XO X X 

Schizochilus ehoriurus Boaden, 1963 X X XO XO XO X X XO XO 

Schizochilus marcusi Boadeu, 1963 X X XO XO XO X X XO 

Schizorhynehoides aculeatus rHardy, 1963 

X 

Sehizorhynehoides karlingi Martens & Sehockaert, 1981 X X X XO 

Schizorhynehoides symmelricus Martens & Sehockaert, 1981 X XO XO XO X XO 

Thylaeorhynehus ambronensis Schilke, 1970 X X XO XO XO X X XO XO 

Thylaeorhynehus caudalus Meixner, 1928 

X 

Thylacorhynehus eonglobalus Meixner, 1928 X X XO XO XO X X 0 0 

Thylaeorhynehuspyriferus Karling, 1950 

XO 

Sehizorhynehoidarum sp. 

Nernatorbynehidae 

XO 

Nematorbynehus parvoacumine Schilke, 1969 

- Karkinorbynehidae 

X 

Cheliplana baadeni Schilke, 1970 X X X X X XO XO 

Cheliplana gemmifera Noldt, 1989 X XO X XO X X 

Cheliplana marcusi (Karting, 1956) X X 0 X 0 0 

Cheliplana microcirrus Noldt, 1989 

XO 

Cheliplana remanei (Meixner, 1928) X X X XO X X X 

Cheliplana stylifera Karling, 1949 X X XO XO XO X X XO XO 0 

Cheliplanilla eaudala Meixner, 1938 X X XO XO XO X X 0 XO 0 

Karkinorhynehus bruneli Schilke, 1970 X X XO XO X X X X 

Karkinorhynehides purpureus Sehilke, 1970 XO X 0 XO 

Diascorbynehidae 

Diascorbynehus rubros Baaden, 1963 

*Dalyellioida 

Provortieidae 

X X XO XO XO X X XO XO 

Hangelhellia ealeeifera Karting, 1940 

X 

Pagaina kinnei Ax, 1970 X X XO XO XO X X XO XO XO 

Pogaina nolons (Ax, 1951) X X 0 0 XO X 

Provortex tubiferus Lutber, 1948 

XO 

Provorlex cf psammophilus Meixner in Ax, 1951 

Graflillidae 

X X X 0 XO X X X XO XO 

Bresslauilla reliela Reisinger, 1929 X X 

Dolyellioida sp. 1 X X XO 0 XO X 0 XO 0 

Dolyellioida sp. 2 

X 

Dolyellioida sp. 3 

X 

Dalyellioida sp. 4 X X XO XO XO X 0 

Dolye/lioida sp. 5 XO 0 

Dolyellioida sp. 6 X 0 0 

Dalyellioida sp. 7 X 0 XO 0 0 

--

- - 

Species composition and diversity of free-living Plathelminthes (Turbellaria) 39 

Table 3 - Number of species per locality and taxon (X: present, not identified to species level). 

De Sinl. Marial:e!te Oostende Btedene Blanken- Ztt- Heist Knokke HdZwin 

Panne ldesbald bag< brugge 

Live Live Live Fixed Live Fixed Live Fixed Live Live Live Fixed Live Fixed Live Fixed 

Acoela X X X X X X X X X X X X X X X X 

Catenulida X X X X X X X X X X X X 0 0 X X 

Macrostomida 4 4 3 3 3 3 3 3 4 5 I 3 3 3 3 4 

Prolecithophora 1 I I 1 1 1 1 I I I 0 0 I 1 0 0 

Proseriata 11 14 11 IJ 9 10 10 11 11 10 3 4 17 19 18 18 

Rhabdocoela 

*Typhloplanoida 4 6 7 7 5 5 6 7 6 6 4 6 12 IJ 9 15 

*Kalyptorhynchia 

uEukalyptorhynchia 7 5 4 6 6 7 4 4 6 9 6 6 8 8 5 5 

**Schizorhynchia 18 26 24 24 18 19 22 25 20 22 1 3 15 21 11 17 

*Dalyellioida 6 7 4 5 4 8 4 6 5 4 5 8 3 5 3 4 

Total 51 63 54 59 46 53 50 57 53 57 20 30 59 70 49 63 

50 % for Heist. These results show that the MgChdecantation 

method is clearly less efficient than the Barnett 

method, and that it has a better efficiency in fine, 

clean, (very) weil sorted sand than in medium, less weil 

sorted sand andlor silty, fine sand. 

Thirty percent of the species were found in 8 to 10 

localities, with only 8 species found in all 10 beaches. 

32 % have a rather general distribution, and are encountered 

in 3 to 7 beaches. About 38 % of the species occur 

only in 1 or 2 localities: 16 species were only found in 

Knokke andlor Het Zwin, of which 5 were unique for 

Knokke and 2 unique for Het Zwin. 

Schizorhynchia generally are the dominant taxon in 

number of species. In Heist however, only a few individuals 

of 3 species are present. The second species richest 

taxon is Proseriata. In Knokke and Het Zwin, the Proseriata 

are represented by the same number of species as the 

Schizorhynchia. These localities contain the most Otoplanidae-species 

(weU known for their preference for 

dynamic habitats) and the most Typhloplanoida-species. 

Strikingly, 9 species with a wide distribution at the Belgian 

coast (found in minimum 8localities) do not occur in 

Het Zwin. 

Table 4 - Diversityand evennessindices for Plathelminthesin six localities. 

Diversity 

The diversity indices H', SI, No, Nb N2 and Ninf. (HlLL 

1973, SOETAERT& HElP 1990 and references therein) aU 

show a significant correlation (Spearman-rank correlation 

test, p

40 P. lOUK & E. SCHOCKAERT 

100 

90 

80 

Propor1ional 

cunUative 

abl.M1dance 

10 

60 

so 

40 

JO 

20 

o 

o 

10 

. 

1 ,. 

Species order 

Fig. I - K-dominancecurves (6 localities). 

For the evenness-indices N10,N' 10,N2I, N' 21>no significant 

differences were found between localities (Kruskall-Wallis 

test, p>0.05), nor was there a significant 

correlation with the sediment characteristics (Spearmanrank 

correlation test, p>0.05). 

Discussion 

With over 130 species in total and 50 to 60 species per 

locality, the Belgian beaches can be considered rich in 

turbellarian species, with a composition ofthe fauna very 

similar to that of similar beaches of the German Island 

Sylt, where studies on the Plathelminthes has been going 

on since the 50-ties (see REISE1988 and references therein). 

As the studies in Sylt show, and as does this one on 

the Belgian coast, some species have a wide distribution, 

while others are restricted to limited habitats. As a general 

mIe, it can be said that the more the habitats diverge, 

the smaller the similarities of the turbellarian fauna are. 

But considering that on the Belgian coast, 38 % of the 

species occur only in one or two beaches, it is clear that 

minor differences in the habitat (even those difficult to 

detect) may have an impact on the turbellarian fauna. 

This also explains why several previously unknown species 

can be found at our coast. 

The diversity of the turbellarian fauna at the Belgian 

coast is also very similar to that noted for similar habitats 

on the German Island Sylt (ARMONIES& HELLWIG-AR- 

MONIES 1987, REISE 1983 a, b, WEHRENBERG 1988, WELL- 

NER& REISE1989), with the H' ranging from 1.20 to 3.35, 

however with higher values for sheltered areas. DrIT- 

MANN(1998) found a H' value of 2.55 or less in sand 

flats adjacent to mangroves in northem Queensland, Australia, 

and own unpublished data on the diversity of 

turbellarians in Ecuadorian open beaches and mangrove 

sand flats of Zanzibar, Tanzania, again all result in H' 

values of 2.0 to 3.0. 

The diversity ofthe free-living Plathelminthes is ofthe 

same magnitude as that of the nematodes and harpacti- 

100 

coid copepods, generally considered the two most dominant 

taxa in the meiofauna, in sandy habitats (BODIN 

1988, HElPet al. 1985, HICKS& COULL1983, WARWICK 

& GEE 1984). It is clear that free-living Plathelminthes 

should be considered when assessing the biodiversity of 

any marine habitat. 

Acknowledgements 

The first author thanks the "Instituut tot Aanmoediging van het Wetenschappelijk 

Onderzoek in Nijverheid en Landbouw" (IWONL) for 

the assignment of a scholarship from 1985 till 1987. 

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Philippe lOUK 

Royal Zoological Society of Antwerp 

Koningin Astridplein 26 

B-2018 Antwerp 

Ernest SCHOCKAERT 

Dept. SBO 

Limburg University Center 

University Campus 

B-3590 Diepenbeek 

41

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