Infaunal macrobenthic community of soft bottom sediment in a tropical shelf

Abstract

Studies of benthic communities in tropical shelf waters are limited. In this study, we deal with the infaunal benthic community of soft bottom sediment of the tropical eastern Arabian Sea shelf. Benthic macroinfauna was sampled with a Smith-McIntyre grab at 30 stations on the continental shelf of the eastern Arabian Sea (northwest coast of India) during January-February (premonsoon) and November (postmonsoon) 2003 from 30 to 200 m depth. The faunal composition, abundance, and diversity of species together with environmental parameters are reported. The sites were clustered into ‘associations’ on the basis mainly of sediment texture and depth. Mean benthic abundance was high in the shallow and intermediate depths and decreased toward deeper areas. Diversity increased with depths up to 100 m during both seasons and decreased beyond 100 m depth. The dominant benthic group was Polychaeta during both seasons. Species richness and diversity were higher during premonsoon compared with postmonsoon. Shallow depths were dominated by deposit-feeding polychaetes, and deeper depths were dominated by deposit and filter feeders such as crustaceans and molluscs. Diversity was high in the medium grain-sized sediment. In the sandy environment, a mollusc–Littorina–Cresis community that dominated during the premonsoon period changed to a Tellina–Mactra community during the postmonsoon period. In the fine sediment, in which the fauna was dominated by deposit feeders such as Prionospio pinnata, no obvious change in the community was observed during the two seasons. From this study, it is deduced that the variations in the macrobenthic community were mainly controlled by sediment texture, depth, and dissolved oxygen.