Composition of macrobenthos from the Central Indian Ocean Basin

The deep sea is well known for its high faunal diversity. But the current interest in its abundant polymetallic nodules, poses a threat to the little known benthic organisms surviving in this unique environment. The present study is the first attempt to document the Indian Ocean abyssal benthic diversity of macroinvertebrates and to investigate its relation to the surface primary production (chl-a), sediment labile organic matter, organic carbon and texture. The present study is based on 87 individuals. Altogether 39 macroinvertebrate genera were obtained from water depths of 4500–5500 m from 23 box cores. Reduction in macrobenthic density was seen towards the southern latitudes. The area was dominated by deposit feeding macrobenthos. Vertically, the fauna was distributed down to 30 cm depth, with the highest faunal density in the top 2–5 cm sediment section. The values for population density were strongly correlated with surface water chl-a and sediment protein, indicating supply of fresh organic matter as a critical factor for maintaining the deep sea benthic diversity and abundance. 1