Changes in rotifer communities regarding to the water-level fluctuations in the floodplain Gemenc, Danube, Hungary

Abstract

The planktonic rotifer communities in three hydrodynamicaly different river-arms at the floodplain of the Danube river at Gemenc have been studied. In the numerous arms the current has different speeds depending on the water level, therefore the physical and chemical parameters (temperature, conductivity, transparency, dissolved oxygen content) are different. We have found forty-six rotifer taxa in the area, but the species-composition changes seasonally. There are therefore big differences in the qualitative and quantitative data between the main arm and the other branches. At high water levels (flood), the rotifer communities of the area are uniformized but, at low water levels the area becomes divided into a series of different water bodies, some near to the lake-state. This phenomenon develops a few days after the flood. The species composition and the abundance relations of the planktonic rotifer communities reflect this effect