1. Department of Biological and Environmental Science, University of Jyväskylä, Jyväskylä 40014, Finland
2. Department of Biology, Dalhousie University, Halifax NS B3H 4R2, Canada
3. Institute of Marine Research, Flødevigen Marine Research Station, N-4817 His, Norway
4. Department of Natural Sciences, University of Agder, N-4604 Kristiansand, Norway