Zooplankton bacterivory at coastal and offshore sites of Lake Erie

Abstract

Two size classes of zooplankton (microzooplankton: 40-200 µm; rotifers and nauplii, but protists were excluded; and macrozooplankton: >200 µm; cladocerans and copepods) bacterivory at coastal and offshore sites in Lake Erie, USA, were determined in situ using both fluorescent and radiolabeled bacteria during the summers of 1993 and 1994. Bacterial abundance, cellular carbon content and productivity were significantly higher at the more eutrophic coastal site (P 60% of total zooplankton biomass, macrozooplankton bacterivory accounted for 54-95% of total bacterivory. Total zooplankton generally consumed <50% of bacterial productivity at the coastal site, while zooplankton bacterivory often exceeded bacterial productivity at the offshore site. Zooplankton consumed an average of 27 and 14% of daily bacterial standing stock at the coastal and offshore site, respectively. Considering the total community bacterivory, zooplankton were often more important bacterial predators than protists. Our results demonstrate the importance of bacteria as a carbon source for zooplankton in the Lake Erie food web, where rotifers can contribute signifi- cantly to total zooplankton bacterivory.