Parrotfish (Scarinae)

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Reef fish with fused beak-like teeth and a pharyngeal mill, which scrape and excavate the reef surface to feed on algae and the microbial and algal turf growing in the substrate. They sit on both sides of this Journey's ledger. As grazers they suppress the fleshy macroalgae that otherwise overgrow bare substrate and block coral larvae from settling, which makes them a condition of recovery rather than a bystander to it. As bioeroders they remove carbonate, grinding rock into sand — the pale sand of a tropical beach is substantially parrotfish faeces — and so belong on the removal side of the carbonate budget. The consequence is that parrotfish abundance is not simply good or bad for a reef: heavy fishing of parrotfish is associated with algal overgrowth after disturbance, while very high excavator biomass on a reef with little living coral accelerates loss of structure. Managing them is managing a rate, not maximising a stock.