Farming damselfish exclude individual grazers by direct attack, and a lone surgeonfish attempting to feed on defended turf is driven off within seconds. The turf inside such territories is nonetheless richer than the surrounding reef, precisely because it has been protected from grazing.
Convict surgeonfish form large feeding schools that move across the reef flat and enter territories en masse. The defender attacks, but with hundreds of fish present it can only displace a few at a time, and the school grazes for long enough to make the raid worthwhile before moving on. The behaviour has been observed repeatedly across Indo-Pacific reefs and is a standard example of schooling used for resource access rather than for predator avoidance.
The same species also enters shallow surge zones and tide pools where larger predators cannot follow, and its transparent postlarvae settle in synchronised waves that make it a common study subject for reef recruitment. Its spine is a mechanical blade like other Acanthurus species, and it is sometimes handled carelessly on that assumption.