Long‐term Annual and Seasonal Changes of Meta‐ and Protozooplankton in Lake Müggelsee (Berlin): Effects of Eutrophication, Grazing Activities, and the Impact of Predation

Abstract

AbstractAnnual changes of rotifers, copepods, cladocerans, the ciliate Epistylis rotans, and larvae of Dreissena polymorpha were analysed for the period 1908–1990. Though food resources increased 6–10 fold in the course of eutrophication, only rotifers and Epistylis increased accordingly. Probably as a result of increased predation pressure crustaceans increased only twice.The seasonal pattern of metazoans and protozoans (flagellates, sarcodines, ciliates) were analysed for 12 and 3 years, resp. During winter and spring, large heterotrophic flagellates and ciliates dominated the zooplankton and were responsible for a pronounced ‐ formerly underestimated ‐ grazing pressure on phytoplankton. In early summer, metazoan filter‐feeders were often able to cause a significant reduction of phyto‐ and protozooplankton. However, during some years, phytoplankton declined in the absence of a pronounced grazing pressure. Field data and experiments revealed that predators were able to regulate the density of cladocerans in early summer (mainly cyclopoids) and summer (mainly Leptodora, smelt and fish juveniles).