Biomass dependent interactions in pond ecosystems: responses of lower trophic levels to fish manipulations

The effects of mature benthivorous cyprinid fish and theirrecruitment on sediment resuspension, turbidity, phyto- andzooplankton, and benthic macroinvertebrates were studied in fourexperimental ponds. The ponds were stocked with bream (Abramisbrama L.), white bream (Blicca bjoerkna L.), roach (Rutilus rutilus L.) and wild carp (Cyprinus carpio L.) of3+–5+ age classes at standing crop biomass varying from 0 to500 kg ha-1. Cyprinids caused an increase in sedimentresuspension and in turbidity, in proportion to their biomass. Meancrustacean biomass did not significantly affect phytoplanktonbiomass due to intense grazing by fish during spring. Ponds withhigh fish stocks showed reduced midge biomass and vegetation coverand increased biomass of predatory invertebrates.