Ostracod biodiversity from shelf to slope oceanic conditions, off central Bay of Bengal, India

Abstract

Thirty seven surface sediment samples collected through a multi-corer in seven transects of ORV Sagar Kanya, SK 308 Leg-1 from off central Bay of Bengal (shelf to slope environment) were analysed for living and dead Ostracoda. The samples, which ranged in water depth from ~ 29 m to 2540 m, yielded a total of 46 species belonging to 32 genera. The ostracod fauna of the Bay of Bengal exhibit a depth-related distribution that is controlled by substrate and hydrographic conditions. Sandy substrates of shallow water depth (~ 28 m) are characterized by Propontocypris sp. and Cytherelloidea malaccaensis. These species are replaced by Neonesidea cracenticlavula and Bairdoppilata paraalcyonicola in high population, which shows positive linear correlation with salinity, temperature and Total Calcium Carbonate (TCC) in the outer shelf ~ 55-73 m. Paijenborchella sp. dominates at ~ 763 m in the bathypelagic zone, giving way to Parakrithella sp. at greater depths of ~ 2540 m on soft-bottom substrates. The fauna represents an interesting mixture of displaced species and others known from bathyal and abyssal depths in the Bay of Bengal, including some pandemic deep sea species. The ostracod faunal diversity is higher in shallower water than in the deeper water, which may be due to the optimum temperature, pH, salinity and substrate. The fauna are comprised of three associations (Shelf/Upper Slope; Slope; Lower Slope/Abyss). A marked faunal turnover occurs at the outer-shelf. Factor Analysis was performed to determine the correlation of water and sediment parameters with the ostracod species. This study provides a detailed account of bathymetry and ostracod biodiversity recorded in the study area.