Teleost community composition and the role of herbivory on the intertidal reef of a small isolated island in north-west Australia

Most of the world's tropical coastal and shelf areas are heavily affected by anthropogenic activities, but the north-west shelf of Australia is considered a 'very low-impact' area. The role of herbivory on coral reefs is recognised, but most of that research comes from reefs with considerable land-based impacts. In this study we sampled the teleost community and evaluated herbivory on the reef platform at Browse Island, a small isolated island 200 km off north-western Australia, using several approaches: (1) tethering of macroalgae; (2) herbivore exclosures; and (3) video footage. In total, 99 teleost species from 26 families were identified. Turf algal consumption was evident and 18 teleost turf consumers were identified. In contrast, no evidence was found of herbivory on large macroalgae, and browsers, the only group able to consume macroalgae, were represented by just four species all belonging to the genus Naso. The lack of diversity among these specialist herbivores may be a consequence of the small surface area of the reef and the distance to other emergent reefs. Based on a model of top-down control of macroalgae, the reef is potentially vulnerable to disturbance. Small isolated reefs can have low resilience despite having low impacts from land.