Variation in the marine bivalve diversity with depth: A case study from benthic assemblages of Bay of Bengal

Abstract

Mollusks are one of the most widely studied phyla used as paleoclimatic proxies. One of the primary drivers of terrestrial diversity is the latitudinal gradient. However, here we focus on marine mollusks to see how oceanographic determinants play a significant role in governing the diversity in addition to latitudes. The factors of diversity studied were species abundance, richness, and evenness, and the diversity index used for the study is reciprocal Simpson's diversity index. The oceanographic determinants which affect the diversity are temperature and salinity and the contents of nitrate, phosphate, and silicate. Here, we account for a detailed study of bivalves collected from three cruises in the western Bay of Bengal across twelve latitudinal bins ranging from 10-21 degrees north. Bivalves were collected from 45 stations, ranging from depths 24-738m below sea level. A total of 422 specimens were collected belonging to 21 families. The most abundant family was Veneridae. Our study shows that the richness, evenness, and diversity index do not show any particular trend with depth across all the latitudinal bins. The maximum value of richness and Simpson’s diversity index corresponds to mid-latitudinal bins in the Krishna Godavari delta where the organic content in the sediment is comparatively high. NMDS results showed random scattering among stations in different depth and latitudinal bins which suggests none of bins can be represented by a particular assemblage. Among oceanographic variables, there was some significant correlation of species evenness with temperature and phosphate content.