Feeding
The strong beak of Bolbometopon muricatum is able to grind the sturdiest corals.
Parrotfish are detritivores and eat a wide variety of microscopic organisms living on and within the substrate. The green humphead parrotfish (Bolbometopon muricatum) include coral (polyps) in their diets. Their feeding activity is important for the production and distribution of coral sands in the reef biome, and can prevent algal overgrowth of the reef structure. The teeth grow continuously, replacing material worn away by feeding.[9] Their pharyngeal teeth grind up the coral and coralline algae[13] the fish ingest during feeding. After they digest the edible portions from the rock, they excrete it as sand, helping to create small islands and the sandy beaches of the Caribbean. The green humphead parrotfish can produce 90 kg (200 lb) of sand each yearOr, very averagely (as there are so many variables i.e. size/species/location/depth etc.), about 275 g per parrotfish per day. While feeding, parrotfish must be cognizant of predation by one of their main predators, the lemon shark. On Caribbean coral reefs, parrotfish are important consumers of sponges.An indirect effect of parrotfish grazing on sponges is the protection of reef-building corals that would otherwise be overgrown by fast-growing sponge species