Long-term changes of cladoceran community in a shallow hypertrophic reservoir in Hungary

The cladoceran, phytoplankton and fish communities were studied in 1991–1998 in Kis-Balaton Water Protection System (KBWPS), Hungary. In the inlet section (western part), the fish stock was lower than in the outlet section (eastern part) and in consequence the cladoceran biomass was higher near the inlet and small-bodied cladocerans occurred in high proportion. In third part called Cassette, the fish stock was lower than in the other parts due to fish kill. The cladoceran biomass was much higher (approximately ten times), and large-bodied species such D. magna were dominant. D. magna occurred during a bloom of cyanobacteria. From 1996 the fish stock decreased to close to 100 kg ha−1 in the inlet and outlet sections and daphnids became dominant in the zooplankton. Ratio of different feeding behaviour of fish offers more information about strength of `top-down control'.