1. Centro de Estudos do Ambiente e do Mar (CESAM) and Department of Biology, University of Aveiro, Campus de Santiago, 3810–193, Aveiro, Portugal
2. Alterra, Wageningen University and Research Centre, P.O. Box 47, 6700 AA Wageningen, The Netherlands
3. Department of Aquatic Ecology and Water Quality Management, Wageningen University and Research Centre, P.O. Box 8080, 6700 DD Wageningen, The Netherlands