Bleaching is the greatest threat facing coral reefs. It occurs when zooxanthellae, the photosynthesizing algae that inhabits coral, ejects itself into the surrounding water and the coral can starve to death if bleached for too long. Zooxanthellae is what gives coral its vibrant colors, and in its absence, coral appears bleached, hance the term "bleaching."
Bleaching can be caused by several factors. If water temperature becomes too warm and leaves the ideal 77 to 84 degree Fahrenheit range, bleaching may occur. This increase in water temperature is caused by Global Warming. (Miami Science Museum)
Global Warming and the release of large ammounts of Carbon Dioxide into the atmosphere has also lead to ocean acidification, or an increase in the pH value of seawater. This acidified seawater has a lower carrying capacity for the more basic Calcium Carbonate, a building block of coral.
Bleaching can also occur if the light reaching coral is distorted by runoff from land or sediments stirred up from the seabed. (Cho, 2011)
BLEACHING