Chronic coral consumption by butterflyfishes

Abstract

Interactions between predators and prey organisms are of fundamental importance to ecological communities. While the ecological impact that grazing predators can have in terrestrial and temperate marine systems are well established, the importance of coral grazers on tropical reefs has rarely been considered. In this study we estimate the biomass of coral tissue consumed by four prominent species of corallivorous butterflyfishes. Sub-adult butterflyfishes (60-70mm, 6-11g) remove between 0.6 and 0.9g of live coral tissue per day, while larger adults (>110mm, ~40-50g) remove between 1.5 and 3g of coral tissue each day. These individual consumption rates correspond to the population of coral-feeding butterflyfishes at three exposed reef crest habitats at Lizard Island, Great Barrier Reef consuming between 14.6g (±2.0) and 19.6g (±3.9).200m-2.day-1 of coral tissue. When standardised to the biomass of butterflyfishes present, a combined reef wide removal rate of 4.2g (±1.2) of coral tissue is consumed per 200m-2.kg-1 of coral-feeding butterflyfishes. The quantity of coral tissue removed by these predators is considerably larger than previously expected and indicates that coral-grazers are likely to play an important role in the transfer of energy fixed by corals to higher consumers. Chronic coral consumption by butterflyfishes is expected to exact a large energetic cost upon prey corals and contribute to an increased rate of coral loss on reefs already threatened by anthropogenic pressure and ongoing climate change.