A story of two tales: The relationship between corals and their symbiotic algae
Coral reefs are complex ecosystems with an enormous diversity of fishes, mammals, reptiles, invertebrates, algae and corals which are at the basis of the entire ecosystem. Corals are made up of hundreds if not thousands of individual coral animals, known as coral polyps. Within each of the individual polyp live photosynthetic algae, which are called Symbiodinium. The symbiotic relationship between the coral animals and the algae is mutually beneficial: the algae produces food to the coral through photosynthesis. The coral provides the algae with nutrients (phosphorus and nitrate) that are scarce in the tropical waters and plenty of light for the symbiotic algae to photosynthesize.
Corals are often pictured as vivid animals displaying bright colors, and this color is provided by the photosynthetic algae. Thus, the bleaching of corals is when the corals expel their symbiodinium and in turn lose their color. The algae utilize light and carbon dioxide to make food through photosynthesis and release oxygen and water. With the rising of water temperature, the algae’s ability to photosynthesize becomes impaired and instead of producing food their make toxic compounds (radicals of oxygen) that can kill the coral. Although both the algae and coral have mechanisms to repair radical damage, prolonged and increased thermal stress creates so many radicals that the coral has to expel its major source of food to stay alive. Corals are able to survive bleaching if repopulated soon, but without the energy provided by photosynthetic algae, corals are much more vulnerable to disease and predation and show reduced ability to reproduce.
If you would like to learn more about coral bleaching, check these sites:
http://oceanservice.noaa.gov/facts/coral_bleach.html
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