SEASONAL-VARIATION IN BACTERIAL AND FLAGELLATE COMMUNITIES OF DEEP-SEA SEDIMENTS IN A MONSOONAL UPWELLING SYSTEM

We investigated bacterial and nanoflagellate densities in the bottom s ediments and overstanding water, during both upwelling and non-upwelli ng seasons, along transects (depths 70-4350 m) in the Arabian Sea. Fla gellate bacterivory was studied in bottom-water samples. There was a s ignificant decrease with depth in benthic bacteria and benthic nanofla gellates, but except for the shallowest station, not in water column b acteria or flagellates. There were two significant differences between the seasons: bacterial density, biomass and cell volume were signific antly larger in the bottom water during the upwelling season, whereas benthic flagellates were significantly more numerous in the sediments in the non-upwelling season. Grazing rates were low, but bacterivory h ad significantly greater impact on bacterial standing stock in the bot tom water during the non-upwelling season. (C) 1997 Elsevier Science L td.