Macrobenthos relative to the oxygen minimum zone on the East Indian margin,Bay of Bengal |
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| Authors: | Akkur V Raman Rayaroth Damodaran Lisa A Levin Thiruchitrambalam Ganesh Yannamani K V Rao Sateesh Nanduri Rakhesh Madhusoodhanan |
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| Institution: | 1. Marine Biological Laboratory, Department of Zoology, Andhra University, Waltair, India;2. School of Marine Sciences, Cochin University of Science and Technology, Kochi, India;3. Center for Marine Biodiversity and Conservation, Integrative Oceanography Division, Scripps Institution of Oceanography, La Jolla, CA, USA;4. Department of Ocean Studies & Marine Biology, Pondicherry University, Port Blair, India;5. Department of Biology, University of Bergen, Bergen, Norway |
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| Abstract: | The Bay of Bengal remains one of the least studied of the world's oxygen minimum zones (OMZs). Here we offer a detailed investigation of the macrobenthos relative to oxygen minimum zone OMZ – DO (dissolved oxygen), concentration <0.5 ml·1?1] at 110 stations off the North East Indian margin (160 and 200 N) featuring coastal, shelf and slope settings (10–1004 m). Macrobenthos (>0.5 mm) composition, abundance and diversity were studied in relation to variations in depth, dissolved oxygen, sediment texture and organic carbon. Using multivariate procedures powered by SIMPROF analysis we identified distinct OMZ core sites (depth 150–280 m; DO 0.37 ml·1?1) that exhibited dense populations of surface‐feeding polychaetes (mean 2188 ind. m?2) represented by spionids and cossurids (96%). Molluscs and crustaceans were poorly represented except for ampeliscid amphipods. The lower OMZ sites (DO > 0.55 ml·l?1) supported a different assemblage of polychaetes (cirratulids, amphinomids, eunicids, orbinids, paraonids), crustaceans and molluscs, albeit with low population densities (mean 343 ind. m?2). Species richness E(S100)], diversity (Margalef d; H’) and evenness (J’) were lower and dominance was higher within the OMZ core region. Multiple regression analysis showed that a combination of sand, clay, organic carbon, and dissolved oxygen explained 62–78% of the observed variance in macrobenthos species richness and diversity: E(S100) and H’. For polychaetes, clay and oxygen proved important. At low oxygen sites (DO <1 ml·l?1), depth accounted for most variance. Residual analysis (after removing depth effects) revealed that dissolved oxygen and sediment organic matter influenced 50–62% of residual variation in E(S100), H’ and d for total macrofauna. Of this, oxygen alone influenced up to ~50–62%. When only polychaetes were evaluated, oxygen and organic matter explained up to 58–63%. For low oxygen sites, organic matter alone had the explanatory power when dominance among polychaetes was considered. Overall, macrobenthic patterns in the Bay of Bengal were consistent with those reported for other upwelling margins. However, the compression of faunal gradients at shallower depths was most similar to the Chile/Peru margin, and different from the Arabian Sea, where the depth range of the OMZ is two times greater. The Bay of Bengal patterns may take on added significance as OMZs shoal globally. |
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| Keywords: | Bay of Bengal diversity East Indian margin faunal assemblages macrobenthos oxygen minimum zone |
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