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article imageWhite sand beaches? — They were made from parrot fish poop

By Karen Graham     Sep 8, 2015 in Science
Don't you just love the pictures in travel magazines of stunning white sand beaches surrounded by clear emerald blue waters? If you have ever wondered where white sand comes from, you may be surprised to learn those grains of sand are parrot fish poop.
NOVA and PBS Digital Studios have produced a series of videos called "Gross Science." One video explains how many beaches in the Caribbean, Hawaii, the Maldives and many other places around the world were made.
White sand is actually the product of bioerosion. And this beautiful, fine-grained sand is created by the parrot fish. For those people lucky enough to have done some snorkeling near a coral reef, you have undoubtedly seen some neon-colored parrot fish. Parrot fish poop makes up 85 percent of a coral reef's sand.
Parrot fish are so named because of their unusual dentition. Their teeth are arranged in such a way along their jawbone that they form a beak, just like a parrot. They use their beak to rasp algae from coral and other rocky surfaces. Occasionally, bits of coral are broken off in the process and are ingested along with the algae.
The coral fragments are literally ground up in the intestines of the parrot fish, milled into a fine sediment that is excreted at the back end, says Chris Perry, a marine geoscientist at the University of Exeter in the U.K. and one of the authors of a study on parrot fish in the Maldives. “And that is then distributed onto the reef. And it’s a way that you can convert coral substrate into sediment grade material," Perry adds.
Newsweek points out that parrot fish can be "sand machines." Citing a 2010 study published in Marine Biology, researchers found that one large parrot fish, Scarus rubroviolaceus, found in Hawaii, is capable of bioeroding up to 380 ± 67 kg (838 pounds) of coral into sandy sediment a year.
A more recent study of parrot fish bioerosion in the Maldive Islands was published in the journal Geology on April 27, 2015. The study points out the importance of protecting parrot fish, especially for maintaining the Maldives, which are already under threat from rising sea levels.
Perry says, “If you take the parrot fish out of these systems you would basically be shutting down a very significant amount of the sort of supply chain for island-building sediment.” Think about how that white sand you're spreading your beach towel on came to be, next time you go to the seashore. And take a moment to think about the ecosystem necessary to creating that sand.
More about white sand beaches, parrot fish poop, Coral reefs, bioeroders, Protection
 
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