Coral Bleaching

About Coral Bleaching: Many reef-building corals harbor tiny algae that live inside their  tissues. These algae use light energy to make sugars, a process known as photosynthesis. A portion of these sugars are given to the coral animal and the coral uses the sugars for energy. 

Corals that lose their algae are affected in the same way. This is the reason why widespread coral bleaching is so problematic. Not all corals die if they are bleached. Some corals are capable of recovering from a bleaching event, while others cannot. Why do you think this would be?

Coral bleaching occurs when the tiny brown colored algae are expelled or removed from the coral animal's tissue. This causes the corals to turn a white color, effectively causing the coral animal to look bleached. When corals lose their algae (also called Symbiodinium), they also lose the source of energy provided by algae photosynthesis.  This would be analogous to if, all of a sudden, you lost the capacity to digest and gain energy from a fraction of the food you ate everyday. As you can see, this would be problematic for you and you might become stressed and more susceptible to diseases. 

Bleached (left) and non-bleached (right) colonies of the coral Porites compressa.

Environmental Conditions that Lead to Coral Bleaching: The incidence of coral bleaching is primarily linked to elevated surface seawater temperatures over prolonged periods of time, but other altered environmental conditions can also cause bleaching. During this bleaching event in Hawaii, coral bleaching was first observed after a 4-week-long period of elevated sea-surface temperatures. The purpose of our research is to understand why elevated sea-surface temperature is linked to coral bleaching; how does increased temperature change the normal physiologies of the coral animal and the algae that live inside their tissues? To learn more, see the science page!