1. Department of Biology, Dalhousie University , 1355 Oxford Street, Halifax NS B3H 4R2 , Canada
2. Maurice Lamontagne Institute, Fisheries and Oceans , 850 Route de la Mer, Mont Joli QC G5H 3Z4 , Canada
3. Institute of Marine Research , Flødevigen Marine Research Station, N-4817 His , Norway
4. Centre for Coastal Research, University of Agder , N-4604 Kristiansand , Norway