Glynn,-P.W.  Coral reef bleaching: Ecological perspectives.
	CORAL-REEFS. 1993. vol. 12, no. 1, pp. 1-17.

Coral reef bleaching, the whitening of diverse invertebrate 
taxa, results from the loss of symbiotic zooxanthellae and/or 
a reduction in photosynthetic pigment concentrations in 
zooxanthellae residing within the gastrodermal tissues of 
host animals. Of particular concern are the consequences of 
bleaching of large numbers of reef-building scleractinian 
corals and hydrocorals. Published records of coral reef 
bleaching events from 1870 to the present suggest that the 
frequency (60 major events from 1979 to 1990), scale (co-
occurrence in many coral reef regions and often over the 
bathymetric depth range of corals) and severity (> 95% 
mortality in some areas) of recent bleaching disturbances are 
unprecedented in the scientific literature. The causes of 
small scale, isolated bleaching events can often be explained 
by particular stressors (e.g., temperature, salinity, light, 
sedimentation, aerial exposure and pollutants), but attempts 
to explain large scale bleaching events in terms of possible 
global change (e.g., greenhouse warming, increased UV 
radiation flux, deteriorating ecosystem health, or some 
combination of the above) have not been convincing. Attempts 
to relate the severity and extent of large scale coral reef 
bleaching events to particular causes have been hampered by a 
lack of (a) standardized methods to assess bleaching and (b) 
continuous, long-term data bases of environmental conditions 
over the periods of interest. An effort must be made to 
understand the impact of bleaching on the remainder of the 
reef community and the long-term effects on competition, 
predation, symbioses, bioerosion and substrate condition, all 
factors that can influence coral recruitment and reef 
recovery. If projected rates of sea warming are realized by 
mid to late AD 2000, i.e. a 2 degree C increase in high 
latitude coral seas, the upper thermal tolerance limits of 
many reef-building corals could be exceeded. Present evidence 
suggests that many corals would be unable to adapt 
physiologically or genetically to such marked and rapid 
temperature increases.