Southeast Asian Coral Reefs - Bleaching

Bleaching

Bleaching is one significant threat to the corals. Bleaching is a term that refers to a process that expels the photosynthetic algae from the corals' "stomachs" or polyps. This algae is called zooxanthellae. It is vital to the reef's life because it provides the coral with nutrients; it is also responsible for the color. The process is called bleaching because when the algae is ejected from the coral reef the animal loses its pigment. Zooxanthellae densities are continually changing; bleaching is really an extreme of what naturally happens. The detrimental exaggeration of the natural occurrence can be explained by the increasing temperature of the oceans which is accused to be a result of the "Greenhouse Effect," or global warming (Blackman and Hughes). Biological oceanographer Paul Falkowski and marine biologist Andrew Baker from the Wildlife Conservation Society study bleaching and why it occurs. Their explanations can be put in their simplest terms as such: the algae's membrane melts from the rise in temperature and, as a result, spits out an "oxygen species" directly into the reef. The animal, in turn, views this process as a threat and ejects the algae as a defense mechanism. Once the zooxanthellae are expelled the coral have nothing to feed off and die. Bleaching has been shown to cause up to 90% mortality rate of the affected corals. However, there is a catch. The reefs that are victims of bleaching have been found to be affected in patches, suggesting that there are several factors that affect the bleaching threshold. Not only that, but both bleached and non-bleached corals are often found right next to each other. These cases are numerous, and the variation and impact of factors (such as species or light) are still being heavily questioned, researched, and are vaguely understood.