Bacteria ingestion by : a mechanism stabilizing biomanipulation?Daphnia galeata: a mechanism stabilizing biomanipulation? in a biomanipulated reservoir: a mechanism stabilizing biomanipulation?

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We determined clearance rates and ingestion rates of Daphnia galeata on bacteria and phytoplankton in order to test if bacteria are an important alternative food resource for daphnids during periods of low phytoplankton biomass in the biomanipulated Bautzen reservoir (Germany). D. galeata was able to feed on bacteria with the same efficiency as on algae during most of the time. In spite of similar clearance rates, bacteria ingestion was usually lower than phytoplankton ingestion due to lower bacterial biomass. Only at low biomass of algae in late fall and during the clear water phase, bacteria contributed up to 87% and 42%, respectively, to total carbon ingestion of D. galeata. However, even a short period of relatively high bacteria grazing by daphnids may be important for biomanipulation. Bacteria might bridge over periods of food limitation of daphnids thus promoting the maintenance of high Daphnia biomass. Therefore, ingestion of bacteria by daphnids is thought to stabilize biomanipulation and may hold a key position in the food web of biomanipulated lakes.

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