Rotifera communities associated with invasive Vallisneria spiralis L. (Hydrocharitaceae) versus native macrophytes in the lakes heated by power stations (Konin lakes, W. Poland)

The role that invasive Vallisneria spiralis L. plays in determining the species richness of the rotifer community was examined in the littoral zone of two heated (by power stations) lakes near Konin (W. Poland) (Lake Licheńskie - area 153.6 ha, max. depth 13.3 m and Lake Ślesińskie - area 148.1 ha, max. depth 25.7 m). Vallisneria spiralis is a thermophilic and vegetative reproducing species which has been recorded in the lakes since the 1990s. It spreads very quickly in the lakes, forming monospecific, dense beds which, force out all other submerged vegetation. Samples were collected in August 2004 on 8 littoral stations of Lake Licheńskie and Ślesińskie. Five-liter samples of water (plankton species) and macrophytes (epiphytic species) were elaborated separately. An analysis of the taxonomic structure of rotifer communities inhabiting single-species Vallisneria beds and mixed-species (Vallisneria plus other macrophyte species) beds showed that both communities were relatively rich in species and similar in terms of species composition. A total of 100 species of Monogononta were identified. Single-species Vallisneria beds were inhabited by 77 species, whereas 82 species were found at stations with mixed vegetation. Species diversity was relatively high in both types of macrophyte assemblages. Numbers of rotifer species inhabiting the single-species Vallisneria beds are among the average values observed in a littoral zone rich in macrophyte species from lakes of different morphometry and trophic state. The above observations confirm part of the conclusions from literature that invasions by new plant species do not always lead to a decline in the habitat value for native animals. Otherwise, the invaded plant creates the habitat easily colonized by the native plankton and epiphytic invertebrates.