Polychaete assemblage driven by substrate composition along the coastal waters of the South-eastern Arabian Sea

The spatial variation in polychaete community structure and sediment composition was studied along the coastal waters of the South-eastern Arabian Sea. Sampling was conducted during the pre-monsoon season (2011-2014) in <100 m water depth with the help of van Veen grab. We identified a total of 71 polychaetes species belonging to 16 families. Cluster analysis showed clear separation based on the species distribution. Canonical Corresponding Analysis (CCA) revealed the close dependence of polychaete species to the sediment texture (fine sand & silty clay). The first assemblage was in the South Region (SR) as the sediment texture between Trivandrum, Cochin and Mangalore were characterized by fine sand. The second species assemblage was observed in the Central Region (CR) at Karwar and Goa where the substrate in this area was characterized by a moderate content of silt. The third assemblage was in the North Region (NR) between Ratnagiri and Mumbai and the sediment in this region was characterized by high content of silt and clay. The SIMPER analysis showed regional species assemblage dominated by Cossura delta (13.48% in the NR), whereas Aphelochaeta multifilis (10.55%) dominated in the SR. Increased richness and diversity patterns in the SR were in contrast with NR. The study suggests that the distinct polychaete assemblages in the region were may be influenced by sediment texture pattern. Therefore, long-term studies could be directed towards the demographic, behavioural, and ecological responses of species assemblages.