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Sea temperatures were normal in Bermuda during
1987, when Bermuda escaped the episodes of coral
bleaching which were prevalent throughout the Caribbean region. Survey transects in 1988 on 4-6 m reefs located on the rim margin and on a lagoonal patch reef revealed bleaching only of zoanthids between May and July. Transect and tow surveys in August and September revealed bleaching of several coral species; Millepora alcieornis on rim reefs was the most extensively affected. The frequency of bleaching in this species, Montastreaannularis and perhaps Diploria labyrinthiformis was significantly
higher on outer reefs than on inshore reefs. This bleaching period coincided with the longest period
of elevated sea temperatures in Bermuda in 38 years
(28.9-30.9~ C inshore, >28 ~ offshore). By December,
when temperatures had returned to normal, bleaching of
scleractinians continued, but bleaching of M. alcicornis on the outer reefs was greatly reduced. Our observations suggest that corals which normally experience wide temperature ranges are less sensitive to thermal stress, and that high-latitude reef corals are sensitive to elevated temperatures which are within the normal thermal range of corals at lower latitudes.