TROPHIC COUPLING OF ROTIFERS, MICROFLAGELLATES, AND BACTERIA DURING FALL MONTHS IN THE RHODE RIVER ESTUARY

Field patterns and experimental results suggested that rotifers, by grazing heterotrophic microflagellates, may have exerted an indirect effect on bacterioplankton concentration. A rotifer population (Synchaeta sp.) oscillated out of phase with total microflagellate (autotrophic and heterotrophic) concentration, and heterotrophic microflagellate concentrations oscillated out of phase with bacterial abundance in the Rhode River (USA). Similar patterns were found in a time-course study of isolated water samples. Grazing experiments indicate that the rotifer cleared the water of both heterotrophic and autotrophic microflagellates at 10 to 16-mu-l h-1 rotifer-1. The apparent predator-prey relationships of rotifer-microflagellate and heterotrophic microflagellate-bacteria were formally defined in a model of a rotifer-microflagellate-bacteria food web using grazing and growth rates from field patterns and experiments. The model successfully mimicked field abundance patterns supporting the hypothesis that rotifers, microflagellates and bacteria form a highly interactive system in which rotifers exert an indirect effect on bacterioplankton.