monitoring of coral reefs in recent years (Ogden et al. 1994).One way of isolating the effect of a complex myriad of environmental factors on corals has been to conduct laboratory studies on individual variables and their interactions. This approach has some limitations because of the sensitivity of most coral species to laboratory handling and because few laboratories can truly imitate field conditions. The use of experimental manipulations in the field offers a useful compromise (D.F. Gleason 1993; Gleason and Wellington 1993, 1995). Ultimately a combination of field and experimental approaches, together with in situ monitoring, will be necessary if our understanding of the proximal causes of bleaching is to be improved. Of the major factors highlighted to date as responsible for extensive coral bleaching in the tropical oceans, this reviewwill concentrateon three which predominate in the literature, namely increased sea temperature, solar radiation (including UVR) and a combination of both factors