渚の危機 瀬戸内海・九州・沖縄の状況 沖縄における干潟の現状

Abstract

Tidal flats in Okinawa are now facing various environmental crises. Large-scale reclamation in the southern central region of Okinawa, where many tidal flats used to exist, has continued since the 1970s. If reclamation keeps up its present pace, almost all of the tidal flats of the southern central Okinawa will disappear in the near future. Tidal flats in northern Okinawa have been greatly affected by clayey silt inflows caused by development on land. One consequence has been simplification of the tidal flat environment and a loss of benthic species diversity. Also, at Manko tidal flat, designated as a wetland of international importance under the Ramsar Convention on Wetlands, rapid sedimentation of clayey silt has led to decreases in benthic animals and plants as well as water birds. Most of the shoreline of Okinawa has been converted or is in the process of being converted to artificial breakwaters, and many forms of life restricted to sandy beach, salt-marsh and coastal wood environments exist on the extreme margin of survival. We have only scarce knowledge of the present state of most organisms living in tidal flats of Okinawa. At the same time, the status of tidal flat environments on Okinawa is worse than it has ever been.