1. Faculty of Biology; Department of Aquatic Ecology and Centre for Water and Environmental Research (ZWU); University of Duisburg-Essen; Essen Germany
2. Institute of Botany; Czech Academy of Sciences; Třeboň Czech Republic
3. Department of Botany and Faculty of Sciences; University of South Bohemia; České Budějovice Czech Republic
4. Laboratoire d'Ecologie des Hydrosystèmes Naturels et Anthropisés; UMR 5023; Biodiversité des Ecosystèmes Lotiques; Université Lyon 1; Villeurbanne Cedex France