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Scaridae: The ParrotfishesParrotfishes are abundant on coral reefs, where they often are the largest component of the fish biomass. They are generally small to medium-sized herbivorous fishes. Depth distribution is primarily 1-30m, with some species occurring down to 80m. Adult scarids are grazing animals, feeding on the close-cropped algal and bacterial mat covering dead corals and rocks, seagrasses, and by crushing bits of coral that may contain invertebrate prey. Juveniles feed on small invertebrates. Parrotfishes feed continuously during the day, often in mixed schools, biting at rocks and corals. They usually scrape some of the coral or ingest sand while feeding and grind this in their pharyngeal mill with the plant food. In pulverizing the coral rock fragments and sand they create substantial quantities of sediment. In many areas they are probably the principal producers of sand. Two types of spawning behaviour have been observed for some scarids. Spawning may take place in an aggregation of initial-phase fish; individual groups of fish dart upward from the aggregation, releasing eggs and sperm at the peak of these upward dashes. The second pattern of reproduction consists of pair-spawning; a terminal male defends a territory from other males, courts females within his territory, and spawns individually with them. At night, some species of Scarus are capable of secreting an enveloping cocoon of mucus in which the fish sleeps until daylight.