1. Graduate School of Engineering and Science, University of the Ryukyus, 1 Senbaru, Nishihara, Okinawa 903-0213, Japan
2. Muroto Schoolhouse Aquarium, 533-2 Murotomisaki, Muroto, Kochi 781-7101, Japan
3. Department of Chemistry, Biology and Marine Science, Faculty of Science, University of the Ryukyus, 1 Senbaru, Nishihara, Okinawa 903-0213, Japan