Large-scale bleaching is damaging the Sekisei Reef, Japan’s largest coral reef, which is located between Ishigaki Island and Iriomote Island [in Okinawa Prefecture]. The Ministry of the Environment (MOE) has found that almost 90% of the coral at the 35 spots surveyed is bleached.
The bleaching is thought to be caused by rises in seawater temperature, and there are reports that bleaching is also occurring in the northern part of Ishigaki Island and near Kagoshima Prefecture’s Yakushima. Scientists and citizen environmental protection groups are concerned that the bleaching will spread further. They are calling for divers and others to provide information to the Sangomap website, where information on coral habitats and bleaching status can be posted.
From the end of July through mid-August, the Ministry of the Environment’s Naha Nature Conservation Office surveyed the health status of coral in the Sekisei Reef from near the water’s surface. In addition to Acropora, a genus with low resistance to stressors such as warmer water temperatures and pollution, some of the highly resistant Porites australiensis was also found to be bleached.
Coral bleaching is the phenomenon where corals expel the photosynthetic algae (zooxanthellae) living in their tissues, causing the coral to appear completely white. Coral can survive a bleaching event and return to its original state if the stress is short term, but it is subject to mortality if the stress is prolonged. From June, the water temperatures in the Sekisei Reef exceed 30 degrees Celsius, which increases the risk of bleaching. There is a chance that 10% of the reef coral is dead. The MOE survey report will be released soon.
With Sangomap [literally, “coral map”], anyone can register the health status of coral they observe. The data appears on a map with any photographs posted. The site aims to provide information for setting nature reserves in the future.