Zooplanktonic grazing is increasingly recognized as an important component of phytoplankton dynamics and composition in natural, north-temperate lakes. The most efficient grazers are species of the cladoceran genus Daphnia, but in southeastern reservoirs this genus is often sparse in abundance, particularly during summer. Further, the dominant daphnia is Daphnia parvula which is a small-bodied species possibly not capable of exerting similar controls on food resources as larger Daphnia species. Experimental exclosure of fishes from zooplankton in Jordan Lake, a eutrophic, 55 km2 reservoir in Piedmont North Carolina, was undertaken to determine if zooplankton would respond sufficiently to influence phytoplankton. Every major crustacean zooplankton taxon doubled its biomass within 2 weeks after protection from predators in at least 1 of six experiments from May to September. The usual numerical dominant, Skistodiaptomus pallidus, increased in every test by at least two-fold. D. parvula increased in...