WHERE does sand come from? There are many sources. But the one described in this article might surprise you. It is a fish that grinds coral into fine sand—the parrot fish!

Parrot fish live in various tropical waters throughout the world. After swallowing crushed coral, they extract tiny food morsels and then expel the rest in the form of sand. To do its job, the parrot fish uses its powerful beaklike jaws and strong back teeth. Some species can live as long as 20 years, without wearing out their teeth.

In some areas, by busily chomping away on dead coral, the parrot fish produces more sand than any other natural sand-making process. Some researchers estimate that a typical parrot fish produces hundreds of pounds (kg) of sand a year.

The parrot fish performs another vital task. As it grazes intensively on dead, algae-coated coral and vegetable material, it also keeps the coral clean. The peculiar diet of parrot fish thus maintains the reef in good condition. Where they and other grazers (herbivores) are absent, the reef quickly gets choked with algae and seaweed. “Some suggest that modern reefs would not exist in their present form if it were not for herbivores,” explains the book Reef Life.

All this activity during the day requires a good rest at night, and here again parrot fish are unusual. Nighttime is dangerous on the reef, since many predators are at large. Parrot fish usually sleep concealed under a ledge, but such a hiding place will not always protect them from a hungry shark.

For additional safety, some parrot fish wrap themselves up for the night. They secrete a protective mucus that envelops them, looking somewhat like a transparent nightgown. Marine scientists believe that this foul-smelling wrapping protects them from predators.

The parrot fish is one of the most visible and attractive fish of the reef. Male and female parrot fish often come in a whole palette of vivid colors, which change as they grow to adulthood. But best of all, parrot fish become quite tame in areas where they are not overfished. So they are some of the easiest fish to observe.

Getting up close to a parrot fish while watching and listening to it munch on coral is something few explorers of a coral reef will ever forget. And as parrot fish parade their finery, they keep their environment healthy for other reef creatures and us humans to enjoy.