1. Centre d’Ecologie Fonctionnelle et Evolutive, CNRS1919 Route de MendeF‐34293Montpellier Cedex 5France
2. National Environmental Research InstituteDepartment of Coastal Zone EcologyGrenåvej 12, KaløDK‐8410RøndeDenmark
3. Institute for Inland Water Management and Waste Water TreatmentPO Box 17NL‐8200AALelystadThe Netherlands