1 Department of Ecoscience, Arctic Research Center, Aarhus University, Roskilde DK-4000, Denmark. Electronic address: cs@ecos.au.dk.
2 Department of Biology, Norwegian University of Science and Technology, Trondheim, Norway; Department of Arctic Technology, The University Centre in Svalbard, Longyearbyen, Norway.
3 Department of Environmental Science, Arctic Research Center, Aarhus University, Roskilde DK-4000, Denmark.
4 Department of Ecoscience, Arctic Research Center, Aarhus University, Roskilde DK-4000, Denmark.