ABSTRACT: Biomass and production of bacterial and phytoplanktonic communities were measured during diurnal cycles at different stations in 3 shallow 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 µg C l^-1 h^-1 and bacterial biomass ranged from 11 to 163 µg C l^-1. A slope of 0.625 (n = 93) for the regression of log-transformed bacterial biomass versus log-transformed production suggests that the bacteria were strongly controlled by bottom-up processes. Ratios between net primary production and bacterial production averaged 67% (range 38 to 140%), indicating that the reservoirs studied can be considered as meso-eutrophic 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 coupling between bacterioplankton and phytoplankton, with a large fraction of primary production routed through heterotrophic bacteria and the microbial loop.

KEY WORDS: Bacteria · Phytoplankton · Eutrophication · Tropical reservoirs

Published in AME Vol. 15, No. 1 (1998) on May 22
ISSN: 0948-3055. Copyright © Inter-Research, Oldendorf/Luhe, 1998