Photo Courtesy of Endangered Species International
Corals live within a very small temperature range of 23ºC-25ºC, meaning that a change of any more than 1ºC-2ºC above or below this temperature can cause coral bleaching and the gradual decline in coral tissue. This is due to the expulsion of zooxanthellae which leads to a decline in chlorophyll followed by a decline in protein levels (Glynn & Croz, 1989). If the change in temperature lasts a few days only a small portion of the zooxanthellae will be expelled from the polyps, however if this lasts for any longer than five weeks, the coral is less likely to retake in zooxanthellae and instead die of oxygen starvation, decreased energy and overheating. If the warm spell only lasts a few days the coral is more likely to survive as only small parts of the coral will be bleached. This also happens when there is a decrease in temperature.