Porter,-J.W.; Fitt,-W.K.; Spero,-H.J.; Rogers,-C.S.; White,- M.W. Bleaching in reef corals: Physiological and stable isotopic responses. PROC.-NATL.-ACAD.-SCI.-USA. 1989. vol. 86, no. 23, pp. 9342-9346. During the late summer to fall of 1987, Caribbean reef corals experienced an intense and widespread discoloration event described as bleaching. Contrary to initial predictions, most bleached corals did not die. However, energy input from zooxanthellae decreased, as estimated from: (i) delta super(13)C values, a measure of the discrimination against super(13)C in super(12)C/ super(13)C assimilation, of skeletal aragonite; (ii) in situ photosynthesis-irradiance measurements; (iii) and tissue biomass parameters of Montastraea annularis and Agaricia lamarcki . The delta super(18)O signal, a measure of the discrimination against super(18)O in super(16)O/ super(18)O assimilation, from M. annularis skeletons demonstrated that this event coincided with abnormally elevated water temperatures.