Observations of bleaching patterns and recovery of massive Porites in the moat of Kudaka Island, Okinawa

Abstract

Coral bleaching is whitening of corals due to loss of zooxanthellae and/or their pigments caused by various environmental stressors (see review Brown 1997, and references therein). In Okinawan coral reefs, Yamazato (1981) reported that the extent of bleaching was different in different species, and suspected that the cause of the coral bleaching was elevated sea water temperature. In the summer of 1998, intense and extensive coral and coral reef bleaching events occurred in various regions in the Ryukyu Islands. The event was more severe than that in 1980 (Yamazato, 1981). It seems that the proximal cause of the 1998 bleaching was also unusual high sea water temperature observed over the wide area. When we visited Kudaka Island (26° 09' N, 127° 53' E) in late July 1998, corals were not bleached in the shallow moat (about 2 m maximum depth at low tide). On October 25, 1998, however, many of coral colonies were already bleached. The coral bleaching was suspected to have started in late August to September as was observed in other localities (Nishihira pers obs, see also Nishihira 1999). Since we found distinct bleaching patterns in some colonies of massive Porites in October 1998, we thereafter photographed them repeatedly to monitor recovery process until March 1999. Although the proximal cause of the bleaching was suspected to be elevated sea water temperature, data records were not available for Kudaka Island.