Transfer of carbon and a polychlorinated biphenyl through the pelagic microbial food web in a coastal ecosystem

In order to estimate fluxes of carbon within the microbial community, seawater was collected in a coastal area off Zanzibar Island, Tanzania, during a rainy season (November 1994) and a dry season (September 1996). Diel experiments were conducted in a 24-L polycarbonate bottle and samples were retrieved every third hour over a period of 30 to 33 h. Abundance and production rates of bacteria, nanoflagellates, and microplankton were determined. To determine possible connections between the fluxes of carbon and the fate of 2,2',4,4',5,5'-hexachlorobiphenyl International Union of Pure and Applied Chemistry (IUPAC) no. 153, a time-course experiment was conducted after the diel experiment. The initial PCB partitioning was similar in the two experiments, but the subsequent distribution among the organism groups was different. In the rainy season experiment, the PCB concentration in the largest size fraction was almost three times higher than during the dry season experiment. This was in line with results from the diel experiments where the carbon Aux through the microbial food web was approximately three times higher during the rainy season than during the dry season experiment. These results suggest that the transfer rate of 2,2',4,4',5,5'-hexachlorobiphenyl through the microbial food web is coupled to the carbon flux.