The Grazing Impact ofDaphnia parvulaon Phytoplankton in a Southeastern, Eutrophic Reservoir
Year: 1994
Type: article
Abstract: 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 four of the tests and rapidly reduced chlorophyll concentrations in each case. Abundance and associated species changes in phytoplankton were negligible without a Daphnia response, but when Daphnia increased cell densities of all taxa including most blue-green algae decreased. Only Anabaena increased in proportion to total phytoplankton units. When these results were examined in a D. parvula grazing model, output suggested phytoplankton declines could be caused solely by increased grazing pressure. These results strongly suggest that fish predation is severely limiting the grazing power of zooplankton in Jordan Lake.
Source: Lake and Reservoir Management
Language: English
Subfield: Environmental Chemistry
Field: Environmental Science
Domain: Physical Sciences
Open Access status: bronze
OpenAlex ID: W2062005704