Spatial structuring of zooplankton communities through partitioning of habitat and resources in the Bay of Bengal during spring intermonsoon

Abstract

Despite advances in oceanographic investigations in the Indian Ocean, zooplankton ecology is still poorly known from the open waters of the Bay of Bengal. In order to understand the vertical and horizontal distribution of zooplankton in the Bay of Bengal during spring intermonsoon, stratified sampling was conducted using a multiple plankton net. We found that higher zooplankton biomass was often associated with mesoscale cold-core eddies. The biomass in the mixed layer was less in the central bay and the near absence of organisms beneath this layer was attributed to the very low dissolved oxygen levels, including suboxia in the northern extent. The copepod diversity was severely reduced here and only a few species specialized to thrive in minimum oxygen concentrations were found in this zone. However, Pleuromamma indica is another copepod that seems to have adapted to the oxygen minimum zone, as seen from its increased numbers and its strong vertical migrating ability to cross the low oxygen barrier. Highly diverse copepod assemblages comprising 129 identified species were found to be vertically structured, mostly through partitioning of habitat and food resources.