Many White Sand Beaches Are Basically Fish Poop

9/7 White Beaches Fish Poop
People walk on a white-sand beach in the province of Matanzas around 135 kilometres (84 miles) from Havana May 5, 2010. Many white sand beaches are actually made up of fish poop. Desmond Boylan/Reuters

Summer unofficially ends on Labor Day, a time when many trek to the beach to lay out on—if you’re lucky—luxurious white sands. But while you’re enjoying the feeling of the sand on your feet, just remember: Much of that sand is actually made up of fish poop.

As explained by this “Gross Science” video, part of a series produced by NOVA and PBS Digital Studios, parrotfish make a living by scraping algae off of coral. Often chunks of coral come off with the algae, and end up in their digestive tract. When digested, that coral is turned into a fine powder that the fish excrete.

RTR1X2SH These humphead parrotfish are sand machines, turning the coral chunks they eat into the white beach material. David Loh / REUTERS

These fish can be sand machines. For example, one 2010 study in Marine Biology found that large parrotfish in Hawaii can churn out 840 pounds of eroded coral—i.e. white sand—per year.

And a single giant humphead parrotfish can produce 11,000 pounds of sand per year, according to the video. That means a significant fraction of the sand in beaches on the Caribbean Sea (including the Gulf of Mexico), Hawaii and elsewhere was once eaten and pooped out by parrotfish.