Figure 1.
Bathymetric map of the Andaman Back-arc Basin including Andaman Back-arc Spreading Centre (ABSC) and locations of the underwater video transects (TVG).
All the transects were located in the Back-arc Basin region only. The TVG-9 and TVG-10 were located on the cratered seamount (CSM) off Nicobar Island, TVG-11 and TVG-12 were located on the back-arc spreading ridge segments, while TVG-13 and TVG-14 were located on the rift valley of the basin floor and on the off-axial highs of the back-arc basin.
Table 1.
Video observations on seamounts (CSM and SM2) and bathyal sea floor (back-arc basin) in the Andaman Sea.
Table 2.
Composition of substratum types used for assigning substrate codes to observed habitats viewed from video images from the TVG in the Andaman Back-arc Basin.
Figure 2.
Composition of substratum types of two seamounts and surrounding sea floor in the Andaman Back-arc basin, with transect codes.
Please see Table 2 for details of substratum types.
Figure 3.
Megafaunal abundance along depth for two seamounts and the surrounding deep sea in the Andaman Back-arc basin.
Figure 4.
Megafaunal group composition along the CSM and SM2 seamounts and basin area in the Andaman Sea Back-arc Basin.
Figure 5.
Structure of the CSM seamount (3D model midified from Kattoju et al. 2010) with accurate locations of the TVG-10 at summit and TVG-9 at flank, and the fauna associated with it.
Megabenthic communities observed on a crater seamount in the Andaman Sea. a: Holothurid; b: Euplectella sp.; c: Gorgonian; d: Squat lobster - Galatheidae; e: Demospongiae attached to a big rock, onboard sample; f: the squat lobster-Liogalathea laevirostris; g: brittle star- Ophiophyllum sp; h: dense population of megafaunal communities (gorgonians, sponges, sea urchins, brittle stars, galatheids) lived on the big boulders and uplifted slabs; i: dense patches of corals (gorgonians); j: Ophiuroidea laid on the cobbles substratum.
Figure 6.
The SM2 seamount with locations of TVG-12 at summit and TVG-11 at flank, and its associated fauna.
a:The bird-nest sponge Pheronema sp; b: Munida sp; c: Pycnogonid; d: Arrow indicating the underwater photograph of bird-nest sponge; e: Black coral attached to the hard substratum.
Figure 7.
Occurrences of motility catagories on both seamounts and the basin area.
Figure 8.
nMDS analysis of substratum types along the study sites in the Andaman Sea, the seamounts CSM and SM2, and the off axis basin.
Table 3.
SIMPER analysis of the substrate on two seamounts (CSM and SM2) in the Andman Back-arc Basin; average abundances (av. abund), average Simper (av. simp), contributed percentage (contrib%) and cumulative contribution (cum%).
Figure 9.
nMDS analysis of megafaunal community along the study sites in the Andaman Sea, the seamounts CSM and SM2, and the off axis basin.
Table 4.
Abundance SIMPER analysis of faunal communities on two seamounts (CSM and SM2) in the Andman Back-arc Basin; average abundance (avg. abund), average similarity (as. simp), contributed percentage (contr%), cumulative contribution (cum%).
Table 5.
SIMPER analysis of average abundance dissimilarity between organism groups A and B on two Andaman Sea seamounts.
Figure 10.
Transect-wise distribution of megafaunal community structure indices (S: number of species, d: Margalef's index, J': evenness, H': Shannon diversity).
Table 6.
RELATE analysis between substratum types and biotic parameters in the Andaman Back-arc-Basin (ABB). Bold numbers indicate significant values.
Table 7.
Linear regression based on Pearson correlation showing the relationship between the substratum types and faunal diversity parameters in the Andaman Back-arc Basin.
Figure 11.
Number of taxa reported from the Indian Ocean seamounts including the present study.
A: Bezrukov, B: Equator (Indian), C: Fred, D: Lena, E: Mount Error Guyot, F: Ob' Seamount, G:Shcherbakov, H: Travin Bank, I: Unnamed Seamounts – 1234, J: Walters Shoal, K: CSM - ABB, L: SM2- ABB.
Figure 12.
Comparison of sponges recorded from seamounts around the globe.
Figure 13.
Map of Pheronema sp. distribution on the world ocean seamounts.
The white circle indicates the new addition of Pheronema sp. from the seamounts in the Indian Ocean.