The importance of live coral for small-sized herbivorous reef fishes in physically challenging environments

Abstract

Tropical coral reefs are facing increasing levels of disturbance, with predictions of ongoing reductions in live coral cover. The response of herbivorous fishes to loss of coral cover was investigated by analysing the relationship between the abundance of different sized herbivorous fishes and live coral cover, on a high flow reef slope and a sheltered back reef on Ningaloo Reef, Western Australia. We found positive relationships between coral cover and the abundance of small (10–20 cm) excavating and scraping parrotfishes on the slope, but a negative relationship between corals and small (10–15 cm) grazers. These relationships were not evident on back reefs. Generally, the abundance of large individuals were not correlated with live coral in either habitat. We suggest that in physically demanding environments small parrotfishes may utilise the structural complexity of corals to resist strong water flow and/or to reduce predation. Small acanthurid grazers may school to reduce energy costs and minimise predation risk. The loss of coral cover appears to be particularly important for small fishes in high energy habitats, especially non-schooling species.