Changes in macrobenthic community structure from estuary to continental slope in the south-east coast of India

The pattern of changes in the macrobenthic community was studied along the south-east coast of India from the estuary to continental slope. A transect perpendicular to the coast was selected for sampling in estuary, inshore region, continental shelf and continental slope. Sampling was done in 16 stations in the depth range of 1.7–1000 m. The community structure was characterized in terms of species composition, abundance, diversity and feeding type. Four taxa were encountered in the study area comprising 181 species of polychaetes, 65 species of molluscs, 47 species of crustaceans and six species of ‘others’ (four echinoderms and two cnidarians). Polychaetes were found to be dominant at all the depths constituting 53.89% of the total abundance and 60.54% of the total number of species. Number of species and Shannon diversity of macrobenthos increased from estuary to shelf region and then decreased. The abundance was found to be maximum in the estuary and minimum in the slope. Carnivorous species were found to be dominant in the estuarine and inshore regions and surface deposit feeders in the shelf and slope regions. Dissolved oxygen decreased gradually from 30 m depth and beyond 150 m the decrease was pronounced due to the presence of the oxygen minimum zone. The distance based linear model (DISTLM) showed the environmental variables to explain about 76.45% of the total variability in macrofaunal distribution. Among the various environmental parameters, total organic carbon, depth and salinity explained more variability than others. Gradual change in community structure was quite evident with increase in depth.