The World-Wide Coral Reef Bleaching Cycle and Related Sources of Coral Mortality

Williams, Ernest; Bunkley-Williams, Lucy

World-wide "coral reef bleaching complexes" occurred in 1979-80, 1982-83 and 1986-88. Each included a "preceding event" 1 year (1979, 1982, 1986) before the most extensive ("main event") bleaching began. The 1986-88 complex also possessed a "following event" (1988). A number of minor bouts also occurred during each complex. Preceding events may be used to predict main bleaching events. We believe the world-wide coral reef bleaching complex "cycle" is caused by increasing global temperatures of the 1980's. The progressive deterioration of inshore regions, including coral reefs, may have contributed to the intensity of the events. El Nino southern oscillation (ENSO) events of 1982-83 and 1986-88, on top of these problems, increased overall seawater temperatures, or provided conditions favoring increased inshore temperatures, to the levels necessary to bleach and kill coral reef photosymbiotic hosts. Decreased temperatures also caused minor bouts in 1988, 1989 and possibly other times. Deterioration of coral reefs has also lowered photosymbiotic hosts' resilience, or resistance to the bleaching process. Our model explaining coral reef bleaching employs increased global temperatures, increasing deterioration of reefs, and ENSO events. These conditions are not only well established, but seem almost certain to continue, The cycle may repeat in 1991 or 1992, possibly with more intensity, and will probably continue and increase until coral dominated reefs no longer exist.