Answer: Fish Excrement

If you’ve ever been to, or even seen photos of the beaches that line the coasts of equatorial nations and islands, then you likely noted how fine and pure white the sand is. It’s absolutely beautiful: green jungle foliage, crystal blue waters, and long stretches of brilliant white sand are a motif in vacation advertisements the world over for a good reason.

What you may not realize is that those beautiful “sugar sand” beaches are the result of the endless toil and food foraging habits of the parrotfish. Many species of parrotfish, such as the green humphead parrotfish, feed on the prolific amounts of algae and microorganisms found on coral reefs. In the process, their hard teeth grind away bits of the reef and tiny pieces of coral end up in the fish’s digestive system along with the food it was foraging for.

When the fish excretes the remains of the food, the ground up coral goes along with it and the end result is a surprisingly large transfer of coral reef to the ocean floor and beaches. A single parrotfish can produce 200 pounds (90 kilograms) of sand per year in this fashion. That glistening white beach is the result of thousands of years worth of parrotfish feasting on coral reefs.

While it might seem at first glance that the parrotfish would be harmful to the reef system, the amount of coral the fish chip away is negligible in comparison to the amount of coral they save by cleaning it of algae, sponges, and other organisms that would smother the reef.