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If shallow water corals become stressed, they can expel their zooxanthellae (symbiotic algae) and take on a stark white appearance. In contrast, deep-sea corals have no zooxanthellae because algae cannot survive where there is no light. Instead, deep-sea corals gain their nutrition by filter feeding organic matter from the water. Some deep-sea corals appear stark white when they are healthy, though they can also come in many other colors.
This branch of Lophelia pertusa was brought up from a depth of 1,250 feet from a reef off the coast of North Carolina. The reef that this branch of coral was taken from is believed to be over 10,000 years old. Photo Credit: Bruce Moravchik/NOAA
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