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Bleaching Away The Beauty Of Coral Reefs

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Bleaching Away the Beauty of Coral Reefs

Pretend you are about to go scuba diving in the ocean. You jump in the water and begin to sink down. As you start surveying the coral reefs around you, something catches your eye. The coral has turned white, and no longer moves with life. This whiteness seems to have spread over a large area of the reef. You no longer see the colorful branches swaying in the current, or the schools of tropical fish swimming through the leaves. This death-ridden reef will never have the same life it once had.

This phenomenon is known as coral reef bleaching. This makes corals unattractive and lifeless. The biodiversity of a reef is important to the ecosystem. There are different organizations that have joined together to stop this from happening, but it will take a long time to repair most of the damage that has already been done. The futures of the reefs are in danger right now. There are many causes of coral reef bleaching.

The biggest concern of oceanographers is the effect global warming is having on the reefs. It is a stress condition that involves a breakdown of the symbiotic relationship between corals and unicellular algae called zooxantheallae. These microscopic plants live within the coral tissue, giving it color and food. One of the first symptoms of bleaching is the loss of color (?Coral Bleaching?). Though a coral does not have color does not necessarily mean it is dead. If there is still tissue on the coral, it still has a chance to live and regain its original appearance (?Global Coral Reef Alliance?). It does not take much to kill coral.

Some corals existed in past geological periods when temperatures were higher that they are today. However, those species disappeared during mass extinctions at the start of the ice ages about 2 million years ago. The ones that survived had the greatest tolerance for cold weather conditions. They have little or no ability to adapt to warmer waters (?Global Coral Reef Alliance?).

Coral lives in a very narrow temperature range. A mere 1-2 degree increase for a period of a few weeks can cause bleaching. In 1978, two men, Coles and Jokiel, ran a laboratory test to see how coral survives in different temperatures. They tested it at 28Ñ", 26Ñ", 24Ñ", and 20Ñ" Celsius. Then they exposed the coral to high temperatures to see what the survival rate was. Between the 28Ñ" and 26Ñ"C groups there was only a 13% of survival (Rosenberg 411). This means the slightest change in average seawater temperature can alter the entire ecosystem of the coral reefs. Every mass bleaching event was followed by periods when sea surface temperatures were 1Ñ"C or more above the average values in the warmest month (?GCRA?). Temperature variations from an extremely cold winter or blistering hot summer are not the only causes of bleaching.

Prolonged exposure to air, especially during a very low tide, freshwater dilution due to heavy rainfall, intense sunlight causing increased ultraviolet radiation, and pollution are all causes of coral bleaching (Wells et al. 54). All of these causes alter the homeostasis that the reef environment needs to live. Various anthropogenic and natural variations in the reef environment can cause the symbiosis to deteriorate.

Solar irradiance affects shallow water coral during the summer. Both UV radiation and photosynthetically active radiation penetrate the coral, causing it to lose its color. Subaerial exposure occurs during a low tide. El Niсo Southern Oscillation (ENSO) caused the sea levels to drop some. Also, tectonic uplifts can induce bleaching. Sedimentation, though uncommon, can cause loading of sediments, which choke off the corals. Freshwater dilution is also rare, but deadly. A storm that generates large amounts of precipitation and runoff can lower the salinity of the reef water, thus killing the corals. Increased inorganic nutrient concentrations such as ammonia and nitrate increase zooxantheallae?s densities 2 to 3 times more. Eutrophicantion is an indirect cause of bleaching. Xenobiotics cause a more localized bleaching as opposed to an entire reef being bleached. It is a result of elevated concentrations of chemical contaminants such as Cu, herbicides, and oil. It reduced the number of zooxanthealles. Epizootics are pathogen bleachers. It is a coral disease that causes patching or whole colony death through the sloughing of tissues. It results in a white skeleton, but should not be confused with the bleached coral (?Odyssey Expeditions?). With all of these factors, it would seem like it is impossible to stop bleaching from happening. Global warming seems to be the main problem though. The effects of this problem are very important, especially when dealing with biodiversity.

Bleaching is detrimental for the ecosystem and the organisms living within it. The organisms face lower protein, lipid, and carbohydrate levels. They encounter problems with skeletal grown and reproductive output. Tissue necrosis in the coral host is also a problem. An effect on the ecosystem is the invasion of the dead coral framework by benthic algae. It also serves as a grazing surface for sponges, infaunal mollusks, and grazing sea urchins and fishes (Birkeland 136). There are three main effects of global warming on fish and fisheries. First of all, the loss of coral cover increases space for fast-growing turf algae. Organic production will increase, and as a result an elevated abundance of herbivores and other trophic groups will be influenced.

Secondly, a loss of coral will lead to a loss of reef diversity. The fish that live there will lose their homes, which will lead to a decrease in fish production. Lastly, the loss of coral will affect the successional stages of algae, which is important to the ecology of reef fishes. The loss will open up space, reduce the intensity of herbivory and, therefore, lead to colonization of the reef benthos by late-successional frondose algae. A dominance of frondose algae lowers benthic production and increases covers of the less palatable algae. The result is the reduced abundance of fish diversity (Rosenberg 165). These three effects all impact the biodiversity that thrives among reefs. It is very important to protect the reefs from dangers.

In 1998, there were some experiments conducted to test these three ideas to see which one is the biggest factor is the problems with fish and fisheries. An increase in surgeonfish which supports the increased organic production idea. There was also a loss of damselfish, butterflyfish, and wrasse which supports the loss of fish hypothesis. The decrease in damselfish numbers in fished reefs exhibited both positively and negatively to increased algae. The bleaching phenomena can be used as a sentinel for the environment.



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