New technology for developing biologically productive shallow area in Ago [Japan] Bay

In Ago Bay, sediment eutrophication and frequent occurrence of hypoxia has caused the deterioration of benthic ecosystem and decrease of biological productivity in recent years. Furthermore, harmful algal blooms and infectious diseases make sustainable pearl culture difficult. It is considered that one of the major causes of these phenomena are stagnation of the material circulation by reduction of the shallow coastal areas. The natural shallow coastal areas were decreased everywhere in the inner parts of the bay by land reclamation and the dike construction. Then we made clear that approximately 70% of the tidal flat and shallow areas have already been decreased in Ago Bay. Therefore, for environmental restoration of Ago Bay as a major site of pearl culture, it is necessary to enhance the biological productivity which these shallow areas provide and to enhance the material circulation around the shallow areas. In this study, the suitable range of sediment quality of tidal flat for benthic species was found to be 3-10mg/g dry weight for chemical oxygen demand and 15-35% for mud content ratio. New technology for enhancing the biological productivity in the reclaimed shallow areas by controlling sediment quality was developed.