The mass-bleaching of coral reefs in the Ishigaki Lagoon, 1998

Abstract

Coral bleaching occurred at various places around the Ryukyu Islands in summer 1998. Several researchers have suggested links to high sea surface temperature. However, the observation of coral bleaching around Ishigaki-jima of the Yaeyama Island Group where the bleaching has been extensive since July shows that there was already a sign of the event during the Baiu rainy season.The study of corals on Ishigaki-jima presents the following:1) Coral bleaching was probably caused by the continued high sea surface temperature from July through September 1998.2) The corals had already been severely damaged by the sedimentation of red soil from the disturbed land surface during the Baiu season of the year which had nearly twice as much rainfall as normal year. The subsequent high sea surface temperature in summer contributed to accelerated bleaching.The observation of bleaching in moats around Ishigaki-jima in summer 1998 suggests that the progress of bleaching be divided into the following three time stages:1) Early stage: from around June 20 through early August2) Mature stage: from middle August through early September3) Final stage: from middle September through middle OctoberThe bleaching process divided by these stages is synchronous, with a time lag, with the seasonal change in sea surface temperature and the prevailing weather conditions in Okinawa.