Coral Bleaching

Topics: Coral, Coral reef, Coral bleaching Pages: 7 (2630 words) Published: February 23, 2014
Chemistry Honors Block 3

Coral Bleaching
There are many ecological problems occurring currently on earth. We hear about ecological problems such as global warming, pollution and deforestation often. But coral bleaching, even though less mentioned is still a very serious ecological problem. Coral reefs are found in shallow tropical waters along the shores of islands and continents. A coral colony is made up of numerous individual coral polyps. A Coral reef is mainly composed of calcium carbonate from both living and dead corals. Many other invertebrates, vertebrates, and plants live with corals, with tight resource coupling and recycling, allowing coral reefs to have extremely high productivity and biodiversity. Coral Reefs are sometimes referred to as “the Tropical Rainforests of the Oceans”. Corals Capture Nutrients and energy in two ways, One, by capturing tiny plankton with their tentacles, and two, through a 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. 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. Corals are very dependent on this symbiotic relationship, receiving up to 90% of their energy from the zooxanthellae the tissues of corals themselves are actually not the beautiful colors of the coral reef, but are instead clear. Healthy corals usually appear tan, brown or green, some types of corals have additional pigments so may appear more blue or purple. The corals receive their coloration from the zooxanthellae living within their tissues. What exactly is coral bleaching? Coral bleaching is a stress condition in reef corals that occurs when either the densities of zooxanthellae decline and/or the concentration of photosynthetic pigments within the zooxanthellae falls, resulting with the breakdown of the symbiotic relationship between corals and zooxanthellae. The term “bleaching’ describes the loss of color that results when zooxanthellae are expelled from the coral polyps or when chlorophyll within the algae are degraded. The symptoms of bleaching include a gradual loss of color as zooxanthellae are expelled from the coral tissue, sometimes leaving corals bone white. Bleaching stress is also exhibited by other reef animals that have a symbiotic relationship with zooxanthellae such as soft corals, giant clams, and some sponges. Bleached Coral looks like white, dull coral. Although, some corals, such as lobe coral, have additional pigments in their tissue, so when they ‘bleach’ they may turn a pastel shade of yellow, blue or pink rather than bright white. Coral bleaching doesn’t always kill the coral, it affects the ability of coral to grow and reproduce as well as increases its susceptibility for disease. Some high-risk locations for coral bleaching include reefs in northwestern Australia, Papua New Guinea and some equatorial Pacific islands like Tokelau.

What Causes coral bleaching to occur? As coral reef bleaching is a general response to stress, it can be triggered by a variety of factors, alone or in combination. It is therefore difficult to unequivocally identify the causes for bleaching events. Temperature can cause coral bleaching because coral live within a relatively narrow temperature margin. Very low and high sea temperatures can trigger coral bleaching. Bleaching events occur during sudden temperature drops accompanying intense upwelling episodes, -3 degrees C to –5 degrees C for 5-10 days, seasonal cold-air outbreaks. Bleaching is much more frequently reported from elevated sea water temperature. A small positive increase of 1-2 degrees C for 5-10 weeks during the summer season will usually trigger bleaching. Another...
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