In Thailand in 1995 not only did a high proportion of colonies re-bleach, but they also bleached at the same position on the colony as they did on 1991. For manyof thesecorals, theeastern half of the colony bleached but the west did not.This was a strikig result apparent on the inner and mid-reef flat for not only Goniastrea aspera but also Platygyra daedalea. Once these corals have achieved a size of approximately 10 cm diameter, they become subject to the influence of higher solar radiation on their western sides, particularly on low spring tides (Brown et al. 1994). This exposure apparently protects the western sides against bleaching thought to be induced primarily by increased sea temperature (and possibly irradiance).