Rising temperatures Corals become bleached when under stress because of changing conditions, such as rising sea water temperature.
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They found that those from resistant colonies were between a half and a third as likely to have become bleached as were the controls.
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The increased water temperatures cause the coral reefs to become "bleached," researchers explained to the CBC, meaning the reefs are sick and lose their color.
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More than two-thirds of the Great Barrier Reef has become bleached in the last two years, and conservationists have been warning for a decade that we need to act now or risk losing our reefs for good.
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The entire shell is also covered with maroon-colored moveable spines. Color is a purplish brown, but they become bleached white when washed ashore. As in other echinoderms, five radial furrows branch from the mouth on the animal's underside. This and other species of Echinarachnius have been around since the Pliocene epoch.
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Turbinaria reniformis is a zooxanthellate coral. It lives in symbiosis with unicellular dinoflagellates known as zooxanthellae. These photosynthetic protists provide their host coral with nutrients and energy, but in order to benefit from this, the coral needs to live in relatively shallow water and in a brightly lit position. In conditions of thermal stress, the coral may expel the zooxanthellae, become bleached and ultimately die.
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Coral hosts become bleached when they lose their zooxanthellae. Difference in symbionts, determined by genetic groupings (clades A-H), may explain thermal tolerance in corals.Sampayo, E.M., Ridgway, T., Bongaerts, P., Hoegh-Guldberg, O. (2008) "Bleaching susceptibility and mortality of corals are determined by fine-scale differences in symbiont type" PNAS Environmental Sciences, 105 (30): 10444–10449. Research has shown that some corals contain thermally-resistant clades of zooxanthellae.
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Outbreaks of barley scab (also known as fusarium head blight) usually occur when there are high moisture conditions during the flowering stages of barley development. The infected crops become bleached in color, shrunken, and discolored and will grow pink spore masses on the barley heads. The disease has the potential to destroy a crop within weeks. The shrunken kernels can become so light that the wind can blow them away from the rest of the crop.
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Coral reefs are important, diverse ecosystems that host a plethora of organisms who contribute different services to maintain reef health. For example, herbivorous reef fish, like the parrotfish, maintain levels of macro algae. The upkeep of sea weed contributes to decreasing space competition for substrate seeking organisms, like corals, to establish and propagate, creating a stronger, more resilient reef. However, when corals become bleached, organisms often leave the coral reef habitat which in turn takes away the services that they were previously supplying.
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Although this coral is common and has a wide range, the International Union for Conservation of Nature lists this species in its Red List of Threatened Species as being "Vulnerable". Under adverse conditions, such as a rise in sea temperature, this coral may expel its zooxanthellae and become bleached. It is then much more susceptible to disease. Coral reefs in general are under threat from a decline in the quality of the habitat through mechanical damage, pollution, sedimentation, ocean acidification and global warming and Pavona cactus faces another threat in that it is collected for the aquarium trade.
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Corals are collected for the aquarium trade, and this may be done with little care for the long-term survival of the reef. Fishing among reefs is difficult and trawling does much mechanical damage. In some parts of the world explosives are used to dislodge fish from reefs, and cyanide may be used for the same purpose; both practices not only kill reef inhabitants indiscriminately but also kill or damage the corals, sometimes stressing them so much that they expel their zooxanthellae and become bleached. Deep water coral habitats are also threatened by human activities, particularly by indiscriminate trawling.
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