Bacterioplankton abundance and production and nanozooplankton abundance in Kenyan coastal waters (western Indian Ocean)

Bacterial abundance, [3H]thymidine incorporation rate and heterotrophic nanoflagellate abundance were measured in the water column along transects perpendicular to the Kenyan coast (western Indian Ocean) during June–July (SE monsoon) and November–December (intermonsoon) 1992. Bacterial abundance was low (less than 6 x 105 cells ml-1). Bacterial production estimated from thymidine incorporation rate at near-coastal stations was higher during the intermonsoon period. Production estimates decreased with depth and distance from the coast. Growth rates of bacteria and heterotrophic nanoflagellate abundance were higher during the intermonsoon, indicating a higher turnover than during the SE monsoon. Grazing rates by nanoflagellates, based on their abundance, were estimated to be 100% or more of bacterial production. Bacteria probably supply only part of the nanoflagellate carbon demand. Bacterial production (BP) was high compared with primary production (PP), with average BPnetPPnet ratios of much greater than 100% and 34% during the SE monsoon and intermonsoon, respectively. Compared with open oceanic regions, both BP and PP in Kenyan coastal waters are low. We conclude that BP is not directly coupled to PP and that recylcled carbon, e.g. via grazing, is an important source for bacterial growth.