Rates of Protozoan Bacterivory in Three Habitats of a Southeastern Blackwater River

Abstract

Although protozoa have been largely disregarded in the trophic structure of lotic systems, they have been shown to be important in lentic and marine environments. As part of a larger study concerning the basis of secondary production in the Ogeechee River, GA, preliminary experiments were done using fluorescently-labelled bacteria to directly measure bacterial grazing by protozoa. Protozoan grazing rates can be as high in moving lotic waters as in still waters as demonstrated by comparing a main channel site, a backwater, and a floodplain pond. In the main channel site during April and May 1988, flagellates and ciliates ingested an average of 17 and 320 bacteria/individual/hr, respectively. When this is multiplied by the high protozoan densities present, an average of 47% of the water-column in the main channel is estimated to be cleared of bacteria by protists each day. Protozoan bacterivory could facilitate carbon flow to higher trophic levels by turning bacteria into larger parcels of carbon and nutrients which are available to a greater portion of the filter-feeding members of communities.