Inter-specific variation in susceptibility to grazing among common reef corals

Abstract

Many species of reef fishes, such as butterflyfishes and wrasses, feed almost continuously and at very high rates upon reef-building corals. This study quantified grazing rates on 4 common reef corals (Acropora hyacinthus, A. millepora, Pocillopora damicornis, and massive Porites) to assess the variation in susceptibility to coral predation. We also assessed the variation in predation intensity within A. hyacinthus and A. millepora by standardising grazing rates by colony surface. Rates of grazing on individual colonies were lowest (0.95 ± 0.33 bites per 20 min; mean ± SE) for massive Porites and highest (16.75 ± 0.30 bites per 20 min) for A. hyacinthus. Within coral species, grazing rates showed a linear increase with increasing size of the colony; however, the intensity of predation showed a negative relationship with increasing colony size. Predation intensity was highest for small to medium sized colonies with a peak intensity of 1.13 ± 0.17 and 0.56 ± 0.09 bites per 100 cm2 per 20 min per colony for for A. hyacinthus and A. millepora colonies (200 to 600 cm2), respectively. In contrast, predation intensity was lowest for both very small and very large colonies, with very small colonies (<200 cm2) rarely being consumed by corallivorous fishes.