The Causes Of Coral Reef Bleaching

Corals dislike warm water about as much as acidity. When oceans get typically warm, corals can eject the algae that symbiotically live in their skeletons, providing food in exchange for shelter. The ejection process is called bleaching, named by the white skeleton left behind when the coral gets sick and, in some cases, dies.

Coral reefs not only protect coastlines and beaches from wave damage and erosion, but also are the basis for the fishing and tourism industries. Dying reefs is a worldwide problem, and evidence shows that 10% of the entire world’s coral has died, and 60% will die by 2020 if existing conditions continue (NOAA 2000). The reason that the Australian Great Barrier Reef is so important is because not only is it the largest barrier reef in the world, but it is also one of the most evolved models of how to best manage and protect the world’s largest reef system (Ornitz 1996). It extends for 2,340 kilometers (km), covers 345,000 square km and contains 2,900 reefs, 300 coral cays and 600 continental islands (White 1999). Historically, it has been ahead of the rest of the world in terms of recognizing and addressing problems associated with reef degradation.

Elevated sea temperatures caused by climate change and extra-bright sunlight can result in coral bleaching. As the water gets warmer, corals will expel the algae known as zooxanthellae that lives in their tissues causing the coral to turn completely white. When temperatures drop, the corals can recover, but they might be vulnerable to disease and when

Dr. James Kerry from James Cook University (2017) explains that, “A temperature change of only one or two degrees for three or four weeks is enough to push corals out of their comfort zones and they then have more stress put upon them” (para. 30). This ethos argument is very effective. Doctor James Cook gives a lot of input on coral bleaching that is very interesting. If coral bleaching isn’t on your radar yet, it will be soon. The coral reef provides homes to an abundant amount of marine life. Bleaching could cause the extinction of many coral species. According to Stephanie Wear, The Nature Conservancy’s director of coral reef conservation (2017), “Recent steamy temperatures indicate a rough year ahead for the world’s coral reefs” (para. 1). About ninety-three percent of climate change heat is absorbed by the ocean. One thing to understand is that corals have a very small

Coral bleaching is normally characterized by the expulsion of the zooxanthellae algae, loss of algal pigmentation, or both. Coral bleaching events have had serious effects on corals and reefs worldwide. What is crucial to the understanding of zooxanthellae expulsion and bleaching is how the density of zooxanthellae within the coral is changing, if at all, under the prevailing range of environmental conditions (Gates and Edmunds, 1999). Over the last twenty years, there has been a dramatic increase in both the frequency and intensity of coral bleaching events. Sixty major bleaching events have been reported between 1960 and 1979, whereas only nine were reported prior to 1979 (Huppert and Stone, 1998). Given the dependence of the coral on this symbiotic algae, it is important to determine the cause of these bleaching events. According to Helvarg (2000, p.12):

Since early 1998, climate change has been demonstrating its effects in increasing the ocean 's temperature (West & Salm, 2003). Warm water stress corals causing the phenomenon known as coral bleaching, by which expulsion of colourful symbiotic algae the zooxanthellae, vital for

Coral bleaching usually occurs when the surface of a sea with coral in it becomes too warm for the coral. When the water heats to as little as one degree higher than normal, coral expels the algae living in its tissue, which causes it to turn completely white. The rise in temperature of the sea surface has been linked mainly to global warming. Other causes of coral bleaching include oxygen starvation caused by an increase in zooplankton, increased solar irradiance, increased sedimentation, bacterial infections, changes in salinity, herbicides, low tide and exposure, cyanide fishing and elevated sea levels. Bleaching events in 2016 were unprecedented, nearly 90% of the coral in the Great

Change in ocean Temperature: increased ocean temperature drastically caused by climate change is the leading cause of coral bleaching.

The bleaching of coral reefs is when warm water forces algae to leave the reef. Once the algae disappear, the coral goes from a vibrant color to a pale white. As one marine biologist said, “You go from a vibrant, three-dimensional structure teeming with life, teeming with color, to a flat pavement...” This bleaching makes the coral more vulnerable to diseases and a greater risk of death. The biggest bleaching events to have occurred in

A hypothesis created by a group of scientists determined that the cause for bleaching was due to stress (Brown and Ogden). This stress is closely linked to salinity changes, exposure to ultraviolet radiation in excessive amounts, huge climate changes and most importantly the increase in warm waters (Douglas ). Corals can survive in water that is between 25˚ and 29˚C. Any water temperature above that will result in the death of algae (Brown and Ogden). High ocean temperatures mixed with solar radiation are attributed to current large-scale bleaching events leading to global climate change, such as El Niño (Douglas ).

The Great Barrier Reef in Australia is experiencing bleaching. According to France-Presse, bleaching of a reef is “coral...that has been stressed by the heat” (France-Presse). When a coral has been “stressed by heat,” (France-Presse) the coral discards the algae that lives within itself which causes the coral to be more susceptible to disease. It can take up to several decades for a coral to recover from bleaching. Because of that fact that most coral does not have enough time to recover, it dies.

Coral reefs are threatened by global warming. They can only live in waters between 18 C and 30 C. Therefore, with the increase in temperature of the surrounding water, there has been an unprecedented increase in the number of coral bleaching events during the past 2 decades (which have had some of the warmest years in history). When ocean temperatures get too high, coral polyps lose the symbiotic algae inside them, causing them to turn white, or "bleach," and eventually die.

Coral bleaching occurs when the microscopic plants (zooxanthellae) are expelled by rising ocean temperature. When there are no microscopic plants such as zooxanthellae, the coral turns white and die. The studies show that throughout the worlds ocean, from the Florida Keys to the Great Barrier Reef of the Australia have been evidence of unique coral bleaching caused by the rising of ocean temperature. In the early 1980s the coral bleaching event has increased because of rapid increase of sea water temperature. Esther et al., investigates growth of Oculina patagonica at multiple environmental conditions in the western Mediterranean Sea. The Oculina patagonia is stony coral specie which is found mostly in the Gulf of Mexico and Caribbean. The coral was basically Atlantic origin which was transferred to Mediterranean Sea.

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.

Coral reefs contain symbiotic algae called zooxanthellae which gives the coral its healthy brownish color. The algae "utilizes sunlight and the coral animal's respired CO2 to produce energy rich compounds that feed the coral host" (AIMS, 2003). When stress factors such as "heat, solar radiation, pollution, reduced salinity and changes in oxygenation" occur around the coral, bleaching can begin (Dennis). When bleaching occurs, the algae, which create nutrients for the coral to feed from, is released due to stresses to the reef. Thus the coral starves and its white calcium carbonate skeleton of the coral becomes visible (AIMS, 2003). But one of the main stresses that contributes to the lifeless white appearance of the coral is the warmer temperatures of the sea surface water.