Abundance and relationship of bacteria with transparent exopolymer particles during the 1996 summer monsoon in the Arabian Sea

Abstract

Bacterial abundance and production, numbers, sizes and concentrations of transparent exopolymer particles (TEP) and total organic carbon (TOC) were measured during the 1996 summer monsoon to understand the relationship between TEP, the most labile particulate organic carbon, and bacteria. While high regional variability in the vertical distribution of TOC was discernible, TEP concentrations were high in surface waters at 18--20°N along 64°E with concentrations well over 25 mg alginic acid equivalents l^-1 due to upwelling induced productivity. Their concentrations decreased with depth and were lower between 200 and 500 m. Bacterial concentrations were up to 1.99 x 10⁸ l^-1 in the surface waters and decreased by an order of magnitude or more at depths below 500 m. A better relationship has been found between bacterial abundance and concentrations of TEP than between bacteria and TOC, indicating that bacterial metabolism is fueled by availability of TEP in the Arabian Sea. Assuming a carbon assimilation of 33%, bacterial carbon demand (BCD) is estimated to be 1.017 to 4.035 g C m-2 d-1 in the surface waters. The observed TEP concentrations appear to be sufficient in meeting the surface and subsurface BCD in the northern Arabian Sea.