1. a Kaldbak Marine Biological Laboratory , FR-180 , Kaldbak , Faroe Islands
2. b Department of Fisheries and Marine Biology , University of Bergen , Bergen High Technology Center, N-5020 , Bergen , Norway
3. c National Environmental Research Institute , P. O. Box 358, DK-4000 , Roskilde , Denmark
4. d University of Trondheim , Trondhjem Biological Station, Bynesvegen 46, N-7018 , Trondheim , Norway
5. e University of Copenhagen , Zoological Museum, Universitetsparken 15, DK-2100 , Copenhagen Ø , Denmark