1. Akkeshi Marine Station, Field Science Centre for the Northern Biosphere, Hokkaido University, Aikappu, Akkeshi, Hokkaido 088-1113, Japan
2. Atomosphere and Ocean Research Institute, the Universty of Tokyo, 5-1-5, Kashiwanoha, Kashiwa-shi, Chiba 277-8564, Japan
3. Notojima Aquarium, 15-40 Notojimamagarimachi, Nanao, Ishikawa 926-0216, Japan