1. Akkeshi Marine Station, Field Science Center for Northern Biosphere, Hokkaido Univesity; Aikappu Akkeshi Hokkaido 088-1113 Japan
2. Atmosphere and Ocean Research Institute, the University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa; Chiba 277-8564 Japan
3. Research Center for Biodiversity, Academia Sinica, Taipei 115; Taiwan
4. School of Marine Biosciences, Kitasato University, 1-15-1 Kitasato, Minami-ku, Sagamihara; Kanagawa 252-0373 Japan
5. Japan Agency for Marine-Earth Science and Technology, 2-15 Natsushima-cho; Yokosuka 237-0061 Japan
6. Marine Biology Section, Department of Biology, University of Copenhagen, Universitetsparken 4, DK-2100; Copenhagen Denmark