Management of fish communities and its impacts on the lower trophic levels in shallow ecosystems in Hungary

Abstract

This study shows that multiyear control of phytoplankton by grazing is possible in otherwise cladoceran dominated ecosystems at low cyprinid fish stocks (around 100 kg ha−1) and where piscivore populations, following manipulation measure, can be sustained at the biomass ratio >15%. This reinforces the idea that fish community structure may be a key to the stability of trophic structures that suppress phytoplankton in ecosystems where otherwise cladoceran plankton dominates. Experimental ponds with lower fish biomass (<150-kg ha−1) had less chlorophyll-a concentration per unit TP than those with higher fish biomass. Regressions of chlorophyll-a vs. total phosphorus in the ponds and Major Lake were not significant at lower fish biomass. However, at higher fish biomass the bottom-up processes dominated across all types of ecosystems studied and the regressions were significant. The biomass of herbivorous Cladocera was significantly higher in ponds with a higher percentage of piscivores.