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What Causes Coral Reef Bleaching?

What Causes Coral Reef Bleaching?

Written by Leisure Pro Staff
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Published on April 8, 2013

Coral reef bleaching is thought to be one of the planet’s best indicators of environmental stress. Coral bleaching is not, as many believe, the death of the coral. It is actually the release of symbiotic, photosynthetic organisms that live within the coral’s tissue. These unicellular organisms are called zooxanthellae and give coral their vibrant colors. When coral is put under stress, the zooxanthellae are released giving the coral a white or “bleached” appearance. Though coral bleaching does not mean the death of the coral, it does leave the organism more vulnerable and likely to die in the future. Coral can recover from a bleaching event, but may never return to its previously robust state.

The most common cause of coral bleaching events is a change in the water temperature. Reefs located in shallow depths or with little water flow are particularly at risk for coral bleaching due to temperature change. Extreme weather or unexpected shifts in current can cause sudden temperature changes that result in the expulsion of zooxanthellae. Most bleaching events caused by change in water temperature are localized however, changing global temperatures have resulted in mass bleaching events. Sixty major episodes of coral reef bleaching have occurred between 1979 and 1990. The resulting coral degradation has had lasting effects on marine life worldwide. In 1998 there was a worldwide bleaching event caused by the super storm El Nino.

Changing temperatures are not the only cause of coral bleaching events. Coral, like all living creatures, can fall victim to infectious disease. Bacteria native to the Mediterranean Sea are notorious for their contribution to coral bleaching events in that region. The bacteria is particularly virulent in warmer weather and will penetrate the coral and produce toxins that eventually lead to major bleaching events.

Perhaps the most devastating coral reef bleaching events have occurred on the Great Barrier Reef. With six major bleaching events since 1980, some areas of the reef have seen up to 90% mortality in their sea life. Though coral does have the ability to recover from such events, coral populations on the Great Barrier Reef have declined almost 50% since the 1980s.

Coral reef bleaching events act as nature’s thermometer. As drastic temperature changes, usually on the high end, are the primary cause of coral bleaching these events are correlated with an increase in global temperatures. As global warming continues to be a worldwide issue, marine biologists believe that coral bleaching events will become more frequent.

Leisure Pro Staff

Leisure Pro Staff

Marketing Director for LeisurePro