Coral Reef Bleaching

Coral reef bleaching, white coloration of the coral due to loss of mutualistic algae, is a stress response to multiple different disturbances both natural and also human impacted (3). Coral bleaching occurs when the Zooxanthellae algae density decreases and the amount of photosynthetic pigments are deminished (2). With the loss of these algae, corals begin to lose much of their required nutrients and begin to die (2). If the stress is not too severe and is not constant, then the corals can regain their Zooxanthellae and can ultimately survive. Unfortunately, when conditions are prolonged they die (1). This loss of nutrients for periods of time cause the coral to have decreased growth and reproduction, and also makes the corals more vulnerable to diseases (2).

Bleached Coral (Due to loss of Zooxanthellae)

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Source: © 2003. Reef Futures. Courtesy Ray Berkelmans, Australian Institute of Marine Science.

This is a picture of the reefs that lose their mutualistic algae, which causes the white coloration.

Healthy Coral

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Coral Bleaching Stressors

Coral reef bleaching is a response to stress and is caused by multiple factors such as: freshwater dilution from runoff, and Inorganic nutrients which are mostly caused by oil spills (1). The main causation of coral bleaching is high water temperature. Temperature increase of only 1-2 degrees Celsius, lasting for over six to eight weeks, is enough to trigger bleaching. When the high temperatures persist for much longer, the corals begin to die. The bleaching of the coral also lowers its ability to repel pathogens, thus making it more vulnerable to disease. Higher temperatures also increase the growth rate of coral pathogens thus giving the coral a small chance of survival.

Temperature change

Many of the other stressors only affect the reefs at small local scales. Temperature affects the reefs on a global scale which deams it a much higher concern (2). "Coral bleaching is one of the most visible impacts of climate change on marine ecosystems"(4). The climate change, or more formally known as global warming, is the increase of Earth's surface temperature. This increase in temperature is due to high levels of carbon dioxide, which is the result of many natural and humanistic impacts as well (5). Coral reefs are very adaptive organisms, they have been around for thousands of years. Unfortunately, the global warming occurring today is occurring in such a small amount of time that corals may not be able to adapt fast enough. Without the protection of the coral reefs, many organisms will ultimately perish. This goes to show that humans are not only affecting the land on which they live, but also the oceans beneath them. It is obvious that seemingly small changes have very large effects. Even if the temperature factor is eliminated, reefs will continue to become destroyed because of other reasons such as over-fishing and overexploitation, just to name a few. It is not just one action that needs to be taken, but many. If these actions are not taken soon, we may lose one, if not both, of our Earth's most biologically diverse ecosystems: the coral reefs and rainforests.