Merghulao, Lina, and M.V.S. Guptha

National Institute of Oceanography, Dona Paula, Goa- 403 004, India,

E-mail: guptha@csnio.ren.nic.in

Biogeographic distribution of coccolithophores from the Bay of Bengal, Northern Indian Ocean

Time series sediment trap samples collected at three mooring sites located longitudinally at northern (NBBT), central (CBBT) and southern (SBBT) regions in the Bay of Bengal have been analyzed for coccolithophores. It has yielded twenty three species of coccolithophores which are represented both by coccospheres and disintegrated individual coccoliths. It was observed that Gephyrocapsa oceanica, is the most abundant species followed by Umbilicosphaera sibogae, Umbellosphaera irregularis, Florisphaera profunda, Emiliania huxleyi, Calcidiscus leptopora and Olithotus antillarum in the shallow traps (1156 to 2558 m depths). Similarly, except for a significant increase in F. profunda at SBBT and CBBT and decrease in the same species at NBBT, the remaining species continue to show similar trend in the deep traps (2146-3011 m depths) also. Highest coccolithophore fluxes were observed at CBBT as against NBBT followed by SBBT. Interestingly, coccoliths affected by very conspicuous dissolution and mechanical break down was observed at all the three sites almost throughout the year which in general may be attributed to intense biological activity. At NBBT, the total coccolithophore flux as also the dominant species such as G. oceanica, U. sibogae, U. irregularis, F. profunda, E.huxleyi etci, display their peak occurrence during September-October, the fag end of southwest monsoon. Whereas, abundance pattern at CBBT is different wherein, the total flux shows a general decrease from February – December except during March-April wherein it shows peak abundance. At SBBT, the peak abundance flux is seen during March – September.