coral reef bleaching
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This document contains 4 citations for sources on the topic of coral bleaching: 1) A website from Jason Buchheim on coral reef bleaching from Marine Biology With Odyssey Expeditions. 2) Information on coral bleaching on the Great Barrier Reef from the reefED education website. 3) Generic citation for images from the rewards website Swagbucks. 4) No other information is provided about the content or authors of the sources cited.
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coral reef bleaching
- 11. Works Cited Buchheim, Jason. "Coral Reef Bleaching." Marine Biology With Odyssey Expeditions - Tropical Marine Biology Voyages!. N.p., n.d. Web. 12 Feb. 2013. <http://www.marinebiology.org/coralbleaching. htm>. "Coral Bleaching on the Great Barrier Reef." reefED - Educate to keep it Great. N.p., n.d. Web. 12 Feb. 2013. <http://www.reefed.edu.au/home/explorer/hot_ topics/coral_bleaching/coral_bleaching_on_the _ great_barrier_reef>. "Images." Earn Reward Points and Redeem Them For Free Stuff at Swagbucks.com. N.p., n.d. Web. 5 Feb. 2013. <http://www.swagbucks.com/>.
Editor's Notes
- Coral reefs are located at low latitudes between 30 degrees North and South. They circle the planet in a band centered on the equator. Coral reefs are absent from shores silted by runoff from large fresh water rivers. This is because they grow in waters that have stable salinity. Heavy rainfall and run off from rivers reduces the salinity. They strive in water that is no more than 27% saline.
- Areas covered in coral reefs have high productivity and biodiversity. Many different species of animals live here like;invertebrates, vertebrates, and plants. Scleractinian corals receive their nutrient and energy resources in two ways. They use the traditional strategy of capturing tiny planktonic organisms with their nematocyst capped tentacles, as well as having an obligate symbiotic relationship with a single cell algae known as zooxanthellae.
- Zooxanthellae live symbiotically within the coral polyp tissues and assist the coral in nutrient production through its photosynthetic activities. These activities provide the coral with fixed carbon compounds for energy, enhance calcification, and mediate elemental nutrient flux. The host coral polyp in return provides its zooxanthellae with a protected environment to live within, and a steady supply of carbon dioxide for its photosynthetic processes. The symbiotic relationship allows the slow growing corals to compete with the faster growing multicellularalgaes because the tight coupling of resources and the fact that the corals can feed by day through photosynthesis and by night through predation. The tissues of corals themselves are actually not the beautiful colors of the coral reef, but are instead clear. The corals receive their coloration from the zooxanthellae living within their tissues.
- Coral reef ecosystems world-wide have been subject to unprecedented degradation over the past few decades. Disturbances affecting coral reefs include anthropogenic and natural events. Recent accelerated coral reef decline seems to be related mostly to anthropogenic impacts (overexploitation, overfishing, increased sedimentation and nutrient overloading. Natural disturbances which cause damage to coral reefs include violent storms, flooding, and high and low temperature extremes.
- Coral live in very specific temperatures. Bleaching events occur during sudden temperature drops accompanying intense upwelling episodes, and seasonal cold-air outbreaks. A small 1-2 degree difference in the summer for 5-10 weeks usually will induce bleaching as well. Both photosyntheticaly active radiation and ultraviolet radiation have been implicated in bleaching. Sudden exposure of reef flat corals to the atmosphere during events such as extreme low tides, and tectonic uplifts can potentially induce bleaching. Few instances of coral bleaching have been linked solely to sediment, but it is possible. Rapid dilution of reef waters from storm-generated precipitation and runoff has been demonstrated to cause coral reef bleaching, this is because it changes the salinity of the water. The optimum salinity for coral to live in is 27%. An increase in ambient elemental nutrient concentrations increases zooxanthellae densities 2-3 times their normal amount. Although eutrophication is not directly involved in zooxanthellae loss, it could cause secondary adverse affects such as lowering of coral resistance and greater susceptibility to diseases. Zooxanthellae loss occurs during exposure of coral to elevated concentrations of various chemical contaminants like Copper, herbicides and oil. Because high concentrations of xenobiotics are required to induce zooxanthellae loss, bleaching from such sources are usually extremely localized and transitory. Pathogen induced bleaching is different from other sorts of bleaching. Most coral disease cause patchy or whole colony death and sloughing of soft tissues.
- Bleaching or the paling on zooxanthellate invertebrates occurs when the densities of zooxanthellae decline, or the concentration of photosynthetic pigments within the zooxanthellae fall. Most corals normally contain around 1,000,000 zooxanthellae per cm squared, and 2-10pg of chlorophyll per zooxanthella. (LOOK THIS UP! Find out what it means for note cards!) When corals bleach they commonly lose 60-90% of their zooxanthellae and each zooxanthellae lose around 50-80% of its photosynthetic pigments.The pale appearance of bleached scleractinian corals and hydrocorals is due to the cnidariean’s calcareous skeleton showing throught the translucent tissues.
- If the stress-causing bleaching is not too severe and if it decreases in time, the affected corals usually regain their symbiotic algae within several weeks or a few months. If the zooxanthellae loss is prolonged and the populations do not recover, the coral host eventually dies.
- There are 3 main hypothesizes out there. The first is that high temperatures and irradiance stressors have been implicated in the disruption of enzyme systems in zooxanthellae that offer protection against oxygen toxicity. The second is that photosynthetic pathways in zooxanthellae are impaired at temperatures above 30 degrees Celsius. And Third is low and high temperatures shock the zooxanthellae and result in a low cell adhesion. This causes an expulsion of both cnidarianendodermal cells and zooxanthellae. But… There’s one more idea out there….. This could be an adaptive mechanism. Coral may discharge their cells to repopulate with a different kind of zooxanthellae. Different strains of zooxanthellae exist both between and within different species of coral hosts, and the different strains of algae show varied physiological responses to both temperature and irradiance exposure.
- The large amount of carbon dioxide humans have put into the air in recent decades has done more than just raise Earth’s global temperature–it has also increased the acidity of the oceans, since carbon dioxide dissolves in sea water to form carbonic acid. Corals have trouble growing in acidic sea water, and the combined effects of increasing ocean temperatures, increasing acidity, pollution, and overfishing have reduced coral reefs globally by 19 percent since 1950. Another 35 percent could disappear in the next 40 years, even without the impact of climate change, according to a report released in October 2010 by the World Meteorological Organization and the Convention on Biological Diversity. Coral loss has been the most severe in the Indian Ocean. Up to 90% of coral cover has been lost. The twin stresses of ocean acidification and increasing ocean temperatures will probably mean that by 2050 it will be difficult for any coral reefs to recover from pollution or major storms.