Coral reef fish
Herbivores

Herbivores feed on plants. The four largest groups of coral reef fishes that feed on plants are the parrotfishes, damselfishes, rabbitfishes, and surgeonfishes. All feed primarily on microscopic and macroscopic algae growing on or near coral reefs.

Algae can drape reefs in kaleidoscopes of colours and shapes. Algae are primary producers, which means they are plants synthesising food directly from solar energy and carbon dioxide and other simple nutrient molecules. Without algae, everything on the reef would die. One important algal group, the bottom dwelling (benthic) algae, grows over dead coral and other inert surfaces, and provides grazing fields for herbivores such as parrotfish.

Parrotfish are named for their parrot-like beaks and bright colours. They are large herbivores that graze on the algae that grows on hard dead corals. Equipped with two pairs of crushing jaws and their beaks, they pulverize chunks of algae-coated coral, digesting the algae and excreting the coral as fine sand.

Smaller parrotfish are relatively defenceless herbivores, poorly defended against predators like barracuda. They have evolved to find protection by schooling, sometimes with other species like shoaling rabbitfish. Spinefoot rabbitfish are named for their defensive venomous spines, and they are seldom attacked by predators. Spines are a last-ditch defence. It is better to avoid predator detection in the first place, and avoid being thrust into risky spine-to-fang battles. So rabbitfish have also evolved skilful colour changing abilities.

Damselfish are a group of species that feed on zooplankton and algae, and are an important reef forage fish for larger predators. They are small, typically five centimetres (two inches) long. Many species are aggressive towards other fishes which also graze on algae, such as surgeonfish. Surgeonfish sometimes use schooling as a countermeasure to defensive attacks by solitary damselfish.
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