Coral bleaching in Okinawa, 1980 vs 1998

Abstract

The author has witnessed two coral bleaching events taken place at Sesoko and Okinawa islands in 1980 and 1998. Although the final reports of the 1998 event are not accessible, the author tries to make some comparisons among the events according to his own report on the 1980 event (Yamazato 1981) and his personal experiences of the 1998 event. Coral bleaching in 1980 around Sesoko Island, Okinawa, Japan appears to have been a local event, while that of 1998 was much more extensive affecting all islands of the Ryukyu Islands and Southern Kyushu. Abnormally high surface temperatures were observed on the reef flat during daytime low tide in the summer of 1980, while it was observed continuously throughout the summer of 1998, affecting not only coral reef waters but also coastal waters both day and night. In 1980, over 40% of coral colonies bleached once and about 10% died, the rest of the bleached corals recovered by the following January. In the 1998 event, according to visual observations of the author made on the same reef section, almost 90% of corals and soft corals bleached and died, with only a few colonies of a few species that recovered. In addition to these personal observations, some results of new surveys are presented and comparisons between the two events are made.