Long Term Grazing Control of Algal Abundance: A Case History

Square Lake, Minn., mimics an ideal of the biomanipulation approach. The lake's zooplankton community is dominated by large (body size) herbivorous cladocerans (Daphnia pulicaria) whose collective grazing abilities have maintained a reduced standing crop of algae, apparently since 1926. The physical and chemical environmental factors that define Daphnia's niche in Square Lake are discussed and include stable stratification, a large hypolimnetic volume, and phosphorus concentrations within certain threshold limits. These environmental limitations seem to be generally important for providing a metalimnetic refuge for Dephnia . Future biotic reconstructions that aim to encourage large-bodied Daphnia should consider these environmental limitations.