Parrotfish are named for their dentition.Their numerous teeth are arranged in a tightly packed mosaic on the external surface of the jaw bones, forming a parrot-like beak with which they rasp algae from coral and other rocky substrates.
Although they are considered to be herbivores, parrotfish eat a wide variety of reef organisms. Species such as green humphead parrotfish include coral in their diet.Their feeding activity is important for the production and distribution of coral sands in the reef biome and can prevent algae from choking coral. The teeth grow continuously, replacing material worn away by feeding.The pharyngeal teeth grind up coral rock that the fish ingests during feeding. After they digest they excrete the rock as sand helping to create small islands and the sandy beaches of the Caribbean. One parrotfish can produce 90 kg of sand each year.