Soft sediment dwelling macro-invertebrates of Rajapur bay, central west coast of India

31-34Thirtyfour species of soft sediment dwelling macro-invertebrates were recorded in Rajapur bay at the proposed effluent discharge location of nuclear power plant. The fauna mainly composed of polychaetes (42.52%), molluscs (39.03%), crustaceans (7.86%), sipunculids (1.23%), echiurids (7.86%) and cephalochordates (1.5%). Deposit feeder spionidae-Prionospio pinnata and filter feeder bivalve-Pecten sp. formed the dominant and co-dominant species respectively. Maximum population density and wet biomass recorded were 2,675 m - 2 (XBAR = 445 +/- 507) and 26.5 g m-2 (XBAR = 6.01 +/- 6.2 1) respectively. Annual benthic production was estimated to be 12.02 g.m-2.y-1. Species diversity varied from 0.91 to 3.61 (XBAR = 2.2 +/- 0.75). High species diversity value showed the stability of the environment. Dominance diversity curve showed eveness of benthic fauna. This was reflected on the competition equilibrium period of the population. Species similarity cluster of different stations were formed largely due to habitat specific and feeding behaviour of the species. The spatio-temporal variations and community structure fluctuations of macro-invertebrates are mainly due to the effect of southwest monsoon and the impact of localized biotic and abiotic factors. Benthic fauna in this bay is in natural ecological balance and free from an apparent effect of environmental imbalances. The base line data generated here can be used to assess the impact of pollution, if any, in future