Infaunal macrobenthos along the shelf waters of the west coast of India, Arabian Sea

The study was carried out to comprehend the infaunal macrobenthic community structure along the shelf region in the Arabian Sea of the west coast of India by collecting samples from every degree square of this shelf. Polychaetes were the most abundant infaunal macrobenthic group (56.97%) and recorded 165 species belonging to 32 families. The study showed an average infaunal benthic biomass (in terms of wet weight) of 3.77 g m^-2 and numerical abundance of 1,367 ind. m^-2. Polychaetes species number, total biomass and total numerical abundance exhibited progressive decrease with increasing depth. Values of diversity indices such as Margalef richness, Pielou's evenness and Shannon diversity exhibited a consistent increase from 30-50 m upto 101-150 m and then a steep decrease to >150 m. ANOSIM of PRIMER showed a significant difference between the polychaetes of near shore and shelf edge. The progressive decrease of temperature and dissolved oxygen with increase in depth was found to be analogous to the decrease in the abundance and biomass of benthic fauna. Dominance of spionids, cirratulids and paraonids among the polychaetes were observed in the oxygen-minimum zone. It is estimated that the tropic support of infaunal benthos to demersal fishery is around 23%. In this study, the average total biomass and abundance were high in muddy substrata whereas diversity was higher in sandy substrata. The present study infers that even if many species are characteristically associated with a given sedimentary habitat, their distributions are rarely confined to that environment.