1. Swedish Board of Fisheries, Institute of Coastal Research, Box 109, SE-74071 Öregrund, Sweden
2. Swedish Board of Fisheries, Institute of Freshwater Research, SE-178 93 Drottningholm, Sweden
3. Husö Biological Station and Department of Biology, Åbo Akademi University, FI-20520 Turku, Finland
4. Finnish Game and Fisheries Research Institute, PO Box 2, FI-00791 Helsinki, Finland
5. Swedish Board of Fisheries, Institute of Marine Research, Box 4, SE-45321 Lysekil, Sweden
6. Department of Marine Benthic Ecology and Evolution, University of Groningen, PO Box 14, 9750 AA Haren, The Netherlands