In Dead Water

CORAL BLEACHING

Corals, especially those which build reefs in tropical, shal- low waters, are highly attuned to their environmental sur- roundings. Bleaching occurs when the corals are subjected to repeated and/or sustained stresses which exceed their tol- erances. When this occurs, the symbiotic algae living in the coral tissue are ejected. The corals loose their colour and their white, calcerous skeleton shines through the transparent tis-

sue. Corals can survive this condition for a short time and even take up their symbionts if the stresses subside. However, if the stresses persist, the corals will die. One well document- ed cause of bleaching is increase of sea surface temperatures (SSTs). A prolonged rise in SST during the hottest months of the year by as little as 1°C above the usual monthly average can result in a bleaching event (Glynn, 1996). The first major

Figure 9. Projected areas of above normal sea temperature where coral bleaching is likely to occur for the SRES A2 scenario by two different models, the PCM (1.7°C increase in 100 years) and the HadCM3 (3°C increase in 100 years) by ca. 2035 (a) and by 2055 (b). Both models project severe annual bleaching in more than 80% of the Worlds coral reefs by 2080 (Donner et al ., 2005).

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