1. Institute of Marine Research , P. O. Box 1870 Nordnes, N-5817 Bergen , Norway
2. Department of Marine Sciences-Tjärnö, University of Gothenburg , 45296 Strömstad , Sweden
3. Institute of Marine Research, Austevoll Research Station , Storebø N-5392 , Norway
4. Institute of Marine Research , Flødevigen, Nye Flødevigveien 20, N-4817 His , Norway
5. IVL Swedish Environmental Research Institute , Kristineberg 566, 45178 Fiskebäckskil , Sweden