1. Department of Environment Conservation, Ehime University, Tarumi 3-5-7, Matsuyama 790, Japan, Science Education Department, De La Salle University, 2401 Taft Avenue, 1004 Manila, Philippines, Department of Environmental Veterinary Sciences, Graduate School of Veterinary Medicine, Hokkaido University, N18 W9 North Ward, Sapporo 060, Japan, and Otsuchi Marine Research Center, Ocean Research Institute, The University of Tokyo, Akahama, Otsuchi, Iwate 028-11, Japan