BIOMASS DEPENDENT INTERACTIONS IN POND ECOSYSTEMS - RESPONSES OF LOWER TROPHIC LEVELS TO FISH MANIPULATIONS

The effects of mature benthivorous cyprinid fish and their recruitment on sediment resuspension, turbidity, phyto- and zooplankton, and bent hic macroinvertebrates were studied in four experimental ponds. The po nds were stocked with bream (Abramis brama L.), white bream (Blicca bj oerkna L.), roach (Rutilus rutilus L.) and wild carp (Cyprinus carpio L.) of 3+-5+ age classes at standing crop biomass varying from 0 to 50 0 kg ha(-1). Cyprinids caused an increase in sediment resuspension and in turbidity, in proportion to their biomass. Mean crustacean biomass did not significantly affect phytoplankton biomass due to intense gra zing by fish during spring. Ponds with high fish stocks showed reduced midge biomass and vegetation cover and increased biomass of predatory invertebrates.