Netherlands Institute of Ecology, Center for Estuarine and Marine Ecology. P.O. Box 140, 4400AC Yerseke, The Netherlands

University of Antwerp, Department of Biology, Environmental Management Research Group, Universiteitsplein 1C, 2610 Wilrijk, Belgium

Netherlands Institute of Ecology, Center for Estuarine and Marine Ecology. P.O. Box 140, 4400AC Yerseke, The Netherlands

now at: University of Florida, Dept. of Fisheries and Aquatic Sciences, 7922 NW 71st Street, Gainesville FL 32653, USA

Vrije Universiteit Brussel, Department of Analytical and Environmental Chemistry, Pleinlaan 2, 1050 Brussel, Belgium

Vrije Universiteit Brussel, Department of Analytical and Environmental Chemistry, Pleinlaan 2, 1050 Brussel, Belgium

University of Antwerp, Department of Biology, Environmental Management Research Group, Universiteitsplein 1C, 2610 Wilrijk, Belgium

University of Antwerp, Department of Biology, Environmental Management Research Group, Universiteitsplein 1C, 2610 Wilrijk, Belgium

Vrije Universiteit Brussel, Department of Analytical and Environmental Chemistry, Pleinlaan 2, 1050 Brussel, Belgium

Netherlands Institute of Ecology, Center for Estuarine and Marine Ecology. P.O. Box 140, 4400AC Yerseke, The Netherlands

Netherlands Institute of Ecology, Center for Estuarine and Marine Ecology. P.O. Box 140, 4400AC Yerseke, The Netherlands