CORAL BLEACHING

Coral bleaching is a response to stress. A stress is some type of change in the environment from the coral's ideal living conditions. The most common stresses that cause bleaching are changes in temperature, salinity, and increased ultra-violet radiation. Some anthropogenic stresses that may contribute to bleaching are nutrient loading from land runoff, increased sedimentation, and other forms of pollution.

Zooxanthellae are algae that live symbiotically inside corals and photosynthesize sugars that corals use for energy. In exchange for providing these sugars, the zooxanthellae get an environment in which to live. Zooxanthellae also give corals their color.

When a coral is stressed, it expels its zooxanthellae. Without zooxanthellae, most corals lose their color and look white or "bleached". A bleached coral has also lost its primary source of food generation (the zooxanthellae) and becomes even more susceptible to disease and death.

If the source of the stress is removed, a coral is usually able to recover over a period of a few months. It will accept new zooxanthellae and will regain its color. However, corals often experience partial tissue loss and, in extreme cases, can die from bleaching.