Eutrophication in Tokyo Bay

Abstract

Tokyo Bay, located in the centre of Japan, has a temperate, humid climate. The bay is an enclosed environment, which is heavily populated and densely used. It is approximately 50-km long and 20-km wide and has an average depth of 15 m. Since 1950, increase in the concentration of population and industry in this river basin has caused radical changes in the coastal areas of Tokyo Bay. Some of these changes were eutrophication and a decline in the area of shallow sandy flats in the bay. As a result of eutrophication, Tokyo Bay has been affected by red tides (algal blooms) approximately 50 times a year and by blue tides (upwelling of hypoxic bottom water) approximately 3 times a year. The area of tidal flats has decreased by approximately 90 % over the last 100 years. These changes can affect the distribution of living organisms in the bay. The iconic richness of biological production in the shallow and tidal flats is under the threat of disappearance. On 26 March 2003, the Tokyo Bay Renaissance Promotion Council endorsed the ‘Action Plan for Tokyo Bay Renaissance’. The goal is to restore the beautiful coastal environment for people to enjoy and sustain its natural biodiversity. The challenge of restoration is just beginning. Important and practical future aims are as follows: (1) to sustain the monitoring campaign with the cooperation of various stakeholders; (2) to create and maintain habitat for benthos, sessile organisms and fish larvae using an ecosystem approach; and (3) to establish public participation mechanisms.