Institute of Marine Research, P.O. Box 1870, N-5817 Bergen, Norway. susanne.balzer@imr.no|Institute of Marine Research, P.O. Box 1870, N-5817 Bergen, Norway. susanne.balzer@imr.no|Institute of Marine Research, P.O. Box 1870, N-5817 Bergen, Norway. susanne.balzer@imr.no