What are the causes of coral bleaching?
Answer:
Coral bleaching refers to the loss of color of corals due to stress-induced expulsion of symbiotic unicellular algae.
Coral bleaching is a vivid sign of corals responding to stress, which can be induced by any of:
* increased water temperatures (often attributed to global warming)
* starvation caused by a decline in zooplankton levels as a result of overfishing.[1]
* solar irradiance (photosyntheticaly active radiation and ultraviolet band light),
* changes in water chemistry
* silt runoff
* pathogen infections
Pollution
Coral bleaching is caused by stress which makes the coral expel the algal cells that normally live within its tissues. The stress is possibly caused by increased water temperatures, solar irradiance, pathogen infections or silt.
Pollution, Human interevntion and change in the aquatic population/demography
As the climate changes, corals can't adapt fast enough, and the changing acidity of the oceans is causing corals to bleach and die.
Coral bleaching is a "canary in the coal mine" and we need to act now or we are in danger of losing bio-diversity which ultimately will result in our own extinction.
What they said.
Alive corals normally display a variety of vivid colors from red to violet. One who often goes to a snorkeling or a diving trip knows about this. These colors are not intrinsic to the corals themselves but are rather due to the presence of zooxanthellae that live in symbiosis with the corals. These microorganisms are photosynthetic and provide the corals with organic carbon, while the coral provides the corals with waste materials. However, recently, there have been reported cases of coral bleaching, i.e. the massive loss of coral color, resulting to while or "bleached" appearances of corals, which is mainly caused by the expulsion of these zooxanthellae out of the coral tissues. This is due to a number of multifactorial reasons, and it is not yet clear whether bleaching is an end effect of the occurrence of a combination of these factors or not:
(1) increased seawater temperatures. Usually corals live in ambient water temperatures of about 18 to 24 degrees. Due to global warming, however, there is a significant increase of seawater temperatures. These temperatures causes lower levels of dissolved oxygen in the water and kills / suffocates the corals. Hence, the coral dies and "vomits" out the zooxanthellae
(2) increased runoff of sediments to the seawater. this causes increased turbidities in the water, blocks off sunlight, and decreases the photosynthetic output of the zooxanthellae and other underwater "plants."
(3) water pollution of noxious and pernicious chemicals. This essentially causes the alteration of seawater characteristics/properties
(4) coral bleaching may be a disease of coralline tissues. there are studies showing coral bleaching is associated with an overgrowth of a particular species of Vibrio bacteria. the details are not yet clear but it may be a case of competition between Vibrio and the zooxanthellae
there are other factors that can contribute to coral bleaching, but it is too long to discuss here. you can just search the internet for more reliable results. or you can search international journals / publications for recent data on coral bleaching all over the world. In the past decades these bleachings are isolated cases in the Pacific and Mediterranean. Recently, however, these cases of bleaching have become frequent on a regular basis. There may be a correlation between these locations of bleaching and the reported increase in ambient temperatures in these regions are shown by NASA.
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