1. Department of Limnology, EAWAG/ETH, Überlandstrasse 133, CH‐8600 Dübendorf, Switzerland
2. Institute of Limnology, Biological Station Lunz, Austrian Academy of Sciences, A‐3293 Lunz am See, Austria
3. Department of Limnology, Limnological Research Center, EAWAG, CH‐6047 Kastanienbaum, Switzerland
4. Institute of Limnology, Mondsee Austrian Academy of Sciences, A‐5310 Mondsee, Austria
5. Université Lyon I, Laboratoire d ‘;Ecologie des Eaux Douces et des Grands Fleuves, Equipe Hydrobiologie et Ecologie Souterraines, 43 Blvd du 11 Novembre 1918, F‐69622 Villeurbanne Cédex, France
6. School of Biological Sciences, Queen Mary and Westfield College, University of London, London E1 4NS, U.K.