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Assessing Coral Bleaching
Inquiry Activity A learning activity by Tom J. McConnell, Ball State University. |
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What is Coral Bleaching and What Causes It?
photo by Oregon State Univ. 2012 CC-BY-SA 2.0
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What Color is Coral?
Coral polyps are clear - they have no color at all. They secrete a skeleton made of calcium carbonate, a chemical is white. So if you see a coral that has colors other than white, the color is created by zooxanthellae! There are many kinds of zooxanthellae, and the type of algae in the coral's tissue determines what color it is. Sometimes corals lose the algae they depend on, and that causes them to become pale or even turn white - and that is "coral bleaching." When that happens, the corals are in danger of starving to death. Why Do Corals "Bleach? When corals are stressed, they eject the zooxanthellae in their tissues. How they do this is not completely understood. But we know that certain environmental problems can cause the stress that may lead to bleaching. These "stressors" can include:
There is good news though! Corals CAN take in more zooxanthellae from the water around them if the stressors are removed before they die. This is why it is so important to notice the bleaching early! |