Studies on Stress Responses of Corals in Japan

Abstract

Coral reefs in Japan are threatened by multiple environmental stresses at both the global and the local scales. Declining water quality in coastal reefs has been reported in the Okinawa region due to red soil runoff, agricultural fertilizers, and antifouling chemicals. Many stud- ies on the stress responses of corals have been conducted by Japanese researchers. For example, metabolic changes due to stresses such as high temperature and chemical dis- charge have been reported in quantitative terms. Antioxidant enzyme activities and mycosporine-like amino acids have been studied as possible defense mechanisms against environmental stress. Moreover, coral bleaching has been frequently reported and actively studied since the 1980s in Japan. The synergistic effects of multiple stressors have also been studied, with several studies reporting accelerated bleaching under conditions of high sea- water temperature and low water quality (high nitrate concentration and high bacterial abundance). The importance of water flow has been extensively studied, and it has been suggested to allow more rapid recovery from bleaching and a higher survival rate. To miti- gate environmental stresses on coral reefs, it is important to evaluate risks due not only to global warming but also to local stresses.