Trophic coupling between bacterial and phytoplanktonic compartments in shallow tropical reservoirs (Ivory Coast, West Africa)

Abstract

Biomass and p]-oduction of bacterial and phytoplanktonic communities were measured during diurnal cycles at different stations in 3 shallo~v tropical reservoirs (Ivory Coast). Investigations were conducted in 1995 during 2 typical hydrological seasons (dry season in March and following rainy season in December). Bacterial production in the plankton ranged from 1.2 to 26.2 pg C 1-' h-' and bacterial biomass ranged from l l to 163 pg C 1-' A slope of 0 625 (n = 93) for the regression of log-transformed bactenal biomass versus log-transformed production suggests that the bactena were strongly controlled by bottom-up processes. Ratlos between net primary product~on and bacterial production averaged 67 % (range 38 to 140%), indicating that the reservoirs studled can be considered as mesoeutrophic ecosystems. Average bacterial carbon demand corresponded to 97% of the net primary production, suggesting that the biological systems studied are based on autotrophic metabolism. These relationships are the result of a close metabolic couphng between bacterioplankton and phytoplankton, with a large fraction of primary production routed through heterotrophlc bacteria and the microb~al loop.