Response of rotifers to hydrochemical and biotic factors

The zooplankton community in an open cast sulphur mine impoundment was investigated over two years. Complicated physical and chemical relationships in this pit ecosystem resulted in an atypical planktonic assemblage. Changes in the rotifer populations were examined over time and space in the pit ecosystem. Only 20 species of rotifers were identified in the impoundment. In winter, Polyarthra dolichoptera coexisted with P. bicerca; in spring, one of the dominant species was Keratella quadrata, while, in summer, Hexarthra fennica, Keratella cochlearis and Synchaeta tremula were all present. In autumn, Filinia longiseta dominated the population. On the border of the oxycline and beneath the thermocline lived Keratella testudo. Thermal and chemical stratification generated five variants of diurnal vertical migrations of planktonic animals including two typical, well-known patterns. Some species were able to penetrate the oxygen-free layer in the hypolimnion. These species were also resistant to low concentrations of hydrogen sulfide. Multidimensional scaling and correspondence analysis identified the following factors as important for rotifers: mineralization and the presence of sulfide with hydrogen sulfide, as well as biotic (predators) or the life supporting parameters: temperature, oxygen. Toxic compounds present in the water, especially sulfides or its derivates, were probably responsible for deformation of the rotifers’ spines in 0.1% of the population.