1. Norwegian Institute for Water Research, Økernveien 94, 0579 Oslo, Norway
2. Department of Biological Sciences, University of Bergen, Thormølens Gate 53, 5008 Bergen, Norway
3. Alfred-Wegener-Institute Helmholtz Centre for Polar and Marine Research, Biologische Anstalt Helgoland, Kurpromenade 201, 27498 Helgoland, Germany