Biodiversity of benthic polychaetes from the coastal waters of Paradip, Bay of Bengal
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Polychaete communities of the subtidal waters off Paradip, Orissa, India (Lat, 20 degrees 05 minutes - 20 degrees 20 minutes N and Long. 86 degrees 35 minutes - 86 degrees 60 minutes E) in the Bay of Bengal were studied on a seasonal basis. Composition, distribution and diversity of macrobenthic assemblage were investigated by deploying a van Veen grab at 17 stations in 10 to 30-m water depths. The subtidal sediment off Paradip coast was predominantly of fine-to-very fine particles and rich in organic carbon (mean=1.59+0.85%, n=17). Macrobenthic community was rich and diverse comprising of annelid worms and small crustaceans. The composition of macrobenthos differed considerably between the seasons. The abundance (density and biomass) of macrofauna was higher at shallower depth (near-shore stations) mainly due to the dominance of polychaetes. A total of 79-macrofaunal invertebrate species belonging to 13 phyla and 45 families were identified. The fauna was mainly composed of polychaetes (41.3%), crustaceans (20.6%), molluscans (15.4%), echiurid worms (7.2%) and echinoderms (2.7%). The contribution of polychaetes in soft sediment macrofauna was almost 50%. Out of 20 tops ranked polychaete species, Nephthys sp., was the important in terms of Biological Index of Dominance (BID), whereas Cossura longocirrata was the most abundant. Both these species had wider distributional range and contributed over 27% to the polychaete density. Diversity of macrofauna was higher at offshore (deeper) stations whereas, density was higher at near-shore (shallower) stations. The lower polychaete diversity at near-shore was due to the persistent physical disturbance (dredging activity). Therefore, this study demands for precautionary measures before allowing further alteration in the sedimentary conditions of the area.
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