How Global Warming Affects Coral Reefs

Temperature and Bleaching

Coral reefs need warm and consistent water temperatures to avoid a fatal phenomenon called bleaching. Coral polyps house algae called zooxanthellae. The two living organisms depend on each other for life. In exchange for safe shelter and nutrients from the coral, the zooxanthellae provide the coral polyps with life-sustaining oxygen, nutrients and color. Increasing sea temperatures caused by global warming are threatening coral reefs. When water temperatures increase, the zooxanthellae are expelled from the coral, leaving the reefs to turn white (known as bleach) and die.

Temperature and Disease

Increased water temperatures caused by global warming stress the coral reefs, leaving them prone to infections. Warmer water provides a breeding ground for virulent strains of fungi and bacteria waiting to strike the stressed coral. According to "The Encyclopedia of Earth," a 1- to 2-degree Celsius rise in temperature can increase the severity of some coral diseases, including white syndrome and black band disease.

Sea Levels

In order for coral reefs to thrive, they need to be located in shallow, clear sun-exposed water so photosynthesis can occur. The average optimum sea depth for coral reefs is between 16 and 49 feet. But the melting of glaciers and thermal expansion of oceans caused by global warming may cause sea levels to rise, which may leave many reefs once located in optimum depths now out of the sun's reach. Reefs located too deep can become weak and vulnerable to storms.

Storm Intensity

For coral reefs to grow, they need exposure to sunlight. As storms pound coastlines, coastal vegetation, designed to prevent runoff into the oceans, is disrupted, thereby allowing sediments to pour into the oceans. High levels of sedimentation restrict the amount of sunlight and can smother the coral. According to the National Wildlife Federation, scientists predict global warming will bring more frequent strong tropical storms.

Acidity

Carbon dioxide (CO2), a major contributor of global warming, can have a direct effect on coral reefs. Approximately 25 percent of CO2 in the atmosphere drops into the oceans, forming carbonic acid. A small amount of CO2 is absorbed by sea creatures and is important to shell development, but too much can be deadly. Excess CO2 changes the ocean's chemistry, causing it to become too acidic. Coral reefs exposed to higher than normal acidity levels can experience slow growth and, by some reports in "Science Daily," could eventually dissolve.

Resources

• National Wildlife Federation on global warming and coral reefs
• The Encyclopedia of Earth on global warming and climate change