Ecological preferences of living benthic foraminifera from the Mahanadi river-dominated north-western Bay of Bengal: A potential environmental impact assessment tool.

The ecological preferences of living benthic foraminifera from the riverine influx dominated eastern continental margin of India have been studied. The living benthic foraminifera were abundant on the upper slope (~100-700 m). Three distinct species assemblages were identified. Assemblage 1 (Ammonia beccari, Pseudononion costiferum, Hanzawaia nipponica, Bolivina frondalis, Bolivina dilatata, Bolivina striatula, Asterorotalia milletti) representing warmer, well-oxygenated water and coarse substrate with low organic carbon is restricted to the inner shelf. Assemblage 2 includes species (Verneuilinulla propinqua, Ammodiscus incertus, Buliminella dubia, Rotaliatinopsis semiinvoluta, Bolivina lowmani, Fursenkoina spinosa) thriving in the regions with abundant food availability and low oxygen concentration on the continental slope. The species in Assemblage 3 (Globocassidulina subglobosa, Epistominella exigua, Gyroidinoides subzelandica, Reophax longicollis, Adercotryma glomeratum, Cystammina pauciloculata, Spiroplectammina biformis) prefer deeper waters with moderate organic carbon and dissolved oxygen. The information of the ecological niches of benthic foraminifera will help in environmental impact assessment and paleoecological studies.