Bacterial abundance and production in the
central and eastern Arabian Sea

N. Ramaiah, S. Raghukumar and Mangesh Gauns

Biological Oceanography Division, National Institute of Oceanography, Dona Paula, Goa 403 004, India

 
Seasonal and spatial variations in bacterial and picoplankton abundances and bacterial production (thy. midine incorporation rates) were determined in the water column up to 150 m in several stations in the central and eastern Arabian Sea. Higher bacterial densities of about 1x10⁹ cells L^-1 were observed during the intermonsoon periods of September and April/May compared to the southwest monsoon period of July/August and the winter period of February/March. Although primary production was low during April/May, bacterial production was much higher during this period unlike July/August. It also showed an increase from the northern to the southern Arabian Sea, suggesting the presence of high amounts of dissolved organic carbon in this area. High picoplankton densities, ranging up to 45 * 10⁶ cells L^-1  were observed during February, particularly in the northern Arabian Sea. Rapid turnover of bacteria during the intermonsoon period of April/May suggests the predominance of a 'microbial loop' in the foodweb and a prevailing source of dissolved organic carbon in the oceanic waters.