Coral reefs are aragonite structures produced by living organisms, found in marine waters with little to no nutrients in the water (too many nutrients would damage the reef). "Coral reefs are made predominantly of stony corals and supported by the limestone skeleton they excrete," says Jennifer Horton of HowStuffWorks.com. "These rainforests of the sea are home to a quarter of all marine fish species. In addition to the variety of marine life they support, coral reefs are also immensely beneficial to humans, buffeting coastal regions from strong waves and storms, providing millions of people with food and jobs and prompting advances in modern medicine."
All too predictably, human behavior is their biggest threat and 70 percent of coral reefs may be gone in less than 40 years if the present rate of destruction continues. In a classic example of human arrogance, rather than addressing the damage, old New York City subway cars are being used to create artificial reefs.
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