[BPT04-10] Seasonal variation in assemblage of planktic foraminifera from the sediment trap samples in the Bay of Bengal
Keywords:planktic foraminifera, Bay of Bengal, sediment trap
We identified 25 species of planktic foraminifers in the samples and 7 species constitute more than 80% of foraminiferal assemblage. The 7 species are divided into three populations: carnivorous spinose species (G. ruber, T. sacculifer and G. siphonifera), herbivorous non-spinose species (G. menardii and N. dutertrei), and opportunistic/upwelling species (G. glutinata, G. bulloides). In the summer and winter monsoon periods, the orders of the increase for foraminiferal species are similar. At first, non-spinose species increase and nearly at the same time opportunistic species become dominant. Subsequently spinose species increase in assemblage which shows the opposite pattern on relative contribution of spinose species and opportunistic species. In winter monsoon periods, the first presence of more opportunistic species in the same living depths may be caused by the deeper mixed layers where the phytoplankton bloom is observed in both of surface and subsurface layers. In contrast to winter monsoon periods, the increase for foraminifers start from subsurface-dwelling non-spinose species and then, surface-dwelling spinose species are dominant in summer monsoon periods. The orders of increase for foraminifers possibly reflect the initiation of the primary and the secondary production in subsurface layer under cloudiness and strong stratification inhibiting the surface propagation.