Influence of terrestrial organic matter loading on the occurrence of red tides and hypoxia in Isahaya Bay, Japan

Abstract

In the year 1997, the inner part of Isahaya Bay on the west coast of Ariake Sea was separated from the sea by dikes, leading to the formation of a freshwater reservoir. Since the Isahaya Reclamation Project began in the 1990s, red tides and hypoxia have become more common in the bay. Eutrophic water from the reservoir is frequently discharged into the bay; therefore, nutrient and organic matter in the discharge may promote the occurrence of the red tides and hypoxia in the bay. In this review, I have discussed the impacts of the discharge on matter cycling, and its contribution to the occurrence of red tides and hypoxia in Isahaya Bay. In particular, I have focused on the interaction between organic matter in the discharge and microbes in Isahaya Bay, which is considered to significantly influence the red tides and hypoxia in this bay.