Beautiful Hawaiian beaches are piles of parrotfish poop
Many animals have the sense to defecate in certain locations, usually away from food and water sources. Sometimes, these dung dumping grounds end up being irresistible to other animals, not because of nutritional needs, or because of a desire for camouflage. Sometimes animals just want to spend the day among the waste products of another species, because, well… we like it! Some of the most beautiful ‘white sand’ beaches in Hawaii aren’t exactly what tourists may imagine, as the pristine shore we play in is actually a huge collection of parrotfish droppings.
Parrotfish aren’t eating rocks and pebbles that eventually wash up on shore. They actually eat algae that grows on corals, which not only feeds the fish but also helps keep the coral from being smothered and killed by the algae. The parrotfish can be a bit vigorous in their feeding habits though, and the beaked mouths for which they were named can actually scrape a bit of the coral up with the algae. Overall, it’s a win for the corals, but this deep-cleaning does mean the parrotfish have to deal with bits of coral in their guts.
Breaking down algae for nutrients isn’t an issue, but the hard structure of the swallowed coral is calcium carbonate. If that were to be digested in stomach acid, it would break down and form a lot of carbon dioxide. Not that you’re likely eating a lot of things like chalk these days, but theoretically you could burp out some of these fizzy byproducts. For a fish who would like to control their buoyancy and general digestion, this is a big enough concern that parrotfish skip having stomachs altogether. To break down food, they chew with internal, pharyngeal jaws. The algae can then be harvested for nutrients while the chunks of coral can be passed along as chemically untouched waste.
The pooped coral can make a big difference to a beach, since a large parrotfish can pulverize and pass up to 800 pounds of particulate a year. As prolific as that pooping is, an Australian species of parrotfish has been credited with as much as one ton of sand production a year, which maybe means the fish need to pay more attention to what they eat. These fish aren’t alone though, as many other types of animals, from sea urchins to worms, play a role in creating Hawaiian beaches via their digestive processes.
My three-year-old said, running into the other room to find his mom: Mommy, there’s a fish that eats the plant and the coral and it comes out as sand and we can go there! My second-grader just asked that I remind her of the sand’s origins if we visit a Hawaiian beach any time soon. Time to call the travel agent, I guess.
Source: Absurd Creature of the Week: This Goofy Fish Poops Out White-Sand Beaches by Matt Simon, Wired