1. Preservation and Research Center City of Yokohama 155‐1 Kawaijyuku‐cho, Asahi‐ward Yokohama Kanagawa 241‐0804 Japan
2. Ecological Risk Assessment and Control Section Center for Environmental Biology and Ecosystem National Institute for Environmental Studies 16‐2 Onogawa, Tsukuba Ibaraki 305‐8506 Japan