Parrotfish
Parrotfish are among the most striking fish on tropical reefs, a family of about 100 species found in warm seas around the world, from the Caribbean to the Red Sea and the Pacific. They are named for their teeth, fused into a hard beak that they use to scrape algae and fragments of dead coral from the reef. They grind that material in their throats and release it as fine white sand, the same sand that covers many Caribbean and Pacific beaches; a single large parrotfish can produce hundreds of kilograms of it a year. Most species change color, and many change sex, as they mature, so females and juveniles often look completely different from adult males. They spend their days grazing in groups across shallow reefs, and at night many wrap themselves in a transparent cocoon of mucus, thought to hide their scent from moray eels and other predators. Their constant grazing keeps algae in check and gives corals room to grow, making them one of the reef's most important residents.
Parrotfish species
There are about 100 species of parrotfish, and the ones a diver sees depend on the sea. In the Caribbean, the most common are the stoplight parrotfish (Sparisoma viride), the queen parrotfish (Scarus vetula), the rainbow parrotfish (Scarus guacamaia), the largest in the Atlantic, and the blue parrotfish (Scarus coeruleus), the Caribbean one that turns solid blue as an adult. In the Indo-Pacific lives the biggest of all, the humphead or bumphead parrotfish (Bolbometopon muricatum), which reaches 1.3 meters and 46 kilograms, moves in herds and uses the bump on its forehead to ram coral; it is listed as Vulnerable. The Red Sea has the rusty parrotfish (Scarus ferrugineus), whose males have a rust colored head and a green tail, the fish in the main photo on this page. Off Brazil lives the greenbeak parrotfish (Scarus trispinosus), listed as Endangered. The blood parrot sold for aquariums is not a parrotfish at all, but a freshwater hybrid of cichlids.
Habitat and distribution
Parrotfish live in the tropical and subtropical waters of the Atlantic, Pacific and Indian Oceans. They thrive on shallow, sunlit reefs, usually between 1 and 30 meters deep, where coral is dense and algae plentiful. The Caribbean has some of the best known parrotfish reefs, from the Mesoamerican Reef off Mexico and Belize to the Bahamas and Jamaica, and the family is just as common on the Great Barrier Reef, across the Coral Triangle of Indonesia and the Philippines, and around the islands of Fiji. The Red Sea has its own species, such as the rusty parrotfish, abundant on the reefs of Egypt, Jordan, Israel, Sudan and Saudi Arabia. Rocky reefs, seagrass beds and sandy lagoons can all serve as habitat at different stages of life, and juveniles often shelter in seagrass meadows or mangroves before moving onto the reef as adults.
Appearance, beak and teeth
Few reef fish are as visually striking as parrotfish. Their most recognizable feature is the beak, made of around 1,000 small teeth arranged in rows and cemented together into solid plates. The teeth are made of one of the hardest materials known in living things, tough enough to scrape rock and coral, and new rows keep growing in as the front ones wear down. Behind the beak, in the throat, a second set of grinding teeth, the pharyngeal teeth, crushes what they bite. Colors vary enormously, not just between species but within the same species depending on age and sex. Juveniles and females tend to be duller, often brown, red or mottled, while adult males display vivid greens, blues and pinks with contrasting facial markings. The difference between life stages is so great that scientists once described some of them as separate species. Most parrotfish are also covered in large, clearly visible scales that give them a somewhat armored look.
Feeding habits
Grazing takes up most of a parrotfish's waking hours. Using their hard beak, they scrape algae and loose fragments of dead coral from reef surfaces, then grind the material down using a set of grinding teeth located deep in the throat, known as pharyngeal teeth. This grinding process separates the organic matter they need from the calcium carbonate in the coral skeleton. The calcium carbonate passes through and is excreted as fine white sand. A large individual can produce several hundred kilograms of sand in a single year, and the humphead parrotfish, the biggest of all, bites off several tonnes of reef every year. Some species also consume living coral tissue, though algae forms the bulk of the diet for most. Their feeding is not random. They often return to the same grazing patches day after day, leaving visible scrape marks on the reef surface.
Behavior
During the day, parrotfish are almost constantly on the move, grazing across the reef in loose groups or alongside other herbivorous fish. Larger males often hold territories and can be aggressive toward rivals. As daylight fades, they retreat to a familiar crevice or ledge and settle in for the night. Many species then do something quite remarkable. They secrete a transparent cocoon of mucus from glands near their gills, surrounding their entire body in about half an hour to an hour. Researchers believe this cocoon helps mask the fish's scent, making it harder for nocturnal hunters such as moray eels to detect them. Most parrotfish also change sex during their lifetime: many start life as females and later turn into fully functioning males, taking on the bright colors of the terminal phase.
Ecological role
Reef ecosystems depend on parrotfish in ways that go well beyond sand production. Algae grows fast and, left unchecked, can smother coral colonies and prevent new coral larvae from settling on the reef surface. By grazing heavily and continuously, parrotfish keep algae populations in check and open up bare patches of rock where young corals can take hold. Studies on Caribbean reefs have shown that reefs with healthy parrotfish populations recover from disturbances, such as bleaching events or storms, significantly faster than those where parrotfish have been overfished. In this sense, they act as one of the reef's most important maintenance crews. Their sand production also replenishes beaches and shallow seafloor sediments across the tropics, a benefit that extends well beyond the reef itself.
