IMPACT OF THE GABCIKOVO HYDROPOWER PLANT-OPERATION ON PLANKTONIC COPEPODS ASSEMBLAGES IN THE RIVER DANUBE AND ITS FLOODPLAIN DOWNSTREAM OF BRATISLAVA

The structure of planktonic copepod assemblages in a by-passed Danube section, and in the adjacent floodplain water bodies, has changed sinc e the Gabcikovo hydropower plant was put into operation. The greatest change occurred in a former side arm (upstream of the village of Dobro host'), which dried out. Changes were observed in the parapotamon-type side arms situated between river km 1840 and 1820, fed artificially w ith water from the head-race canal. The abundance of euplanktonic cope pod species decreased, while that of tychoplanktonic species increased . Summer zooplankton biomass decreased. Definitive, but less extreme, changes occurred in the copepod assemblage in the open-water areas of the former main channel of the Danube, and in the plesiopotamon-type s ide arms in the affected river section. These results suggest that the water supply provided to the by-passed floodplain is unable to mainta in the previous habitat diversity, nor its planktonic assemblages spec ies diversity.