Eight 2-week limnocorral (LC) experiments were performed in Lake Lucerne, Switzerland, during 1982Switzerland, during -1984 to study the effects of biomanipulation. The large zooplankton were removed by 95-pm plankton nets in some LCs and different phosphorus fertilization regimes were applied. The chlorophyll a and sestonic POC and PP concentrations decreased significantly in the presence of crustacean zooplankton, whereas algal biomass was 'less affected. Within the short period of 2 weeks this "top-down" regulation seemed to be balanced by "bottom-up" control, because phosphate fertilization and favorable light conditions stimulated phytoplankton production and increased seston concentrations. The significant shift from nanoplankton to net plankton in both the filtered and control LCs, which caused the sedimentation rates to increase during all the experiments, could not be attributed solely to selective zooplankton grazing but was also induced by different algal nutrient strategies. In the control (unfiltered) LCs, the herbivorous crustaceans (usually ~80% Daphnia spp.) increased POC and PP sedimentation by 14-50 and 25-57% due to fecal pellet production.