Indirect benefits of high coral cover for non-corallivorous butterflyfishes

Abstract

Extensive coral loss often leads to pronounced declines in the abundance of fishes, which are not necessarily limited to those fishes that are directly reliant on live coral for food or shelter. This study explored changes in the abundance of two non-corallivorous butterflyfish, Chaetadon auriga and Chaetodon vagabundus, during declines in coral cover at Lizard Island, northern Great Barrier Reef, caused by localised outbreaks of crown-of-thorns starfish (COTS). At North Reef, where COTS caused significant coral depletion, the abundance of C. auriga declined from 1995–1996 to 1997–1999, whereas abundance was unchanged at Washing Machine Reef, which was relatively unaffected by COTS. Abundance of C. vagabundus did not vary through the course of this study at either site. To better understand inter-specific differences in the responses of non-corallivorous butterflyfishes, feeding rates of C. auriga and C. vagabundus were quantified across sites with varying coral cover. Feeding rates of C. auriga were significantly and positively correlated with live coral cover. In contrast, feeding rates of C. vagabundus did not differ among sites with varying levels of live coral cover. This study shows that C. auriga is negatively affected by localised coral depletion, possibly because its prey is more abundant in coral-rich habitats. C. vagabundus, meanwhile, is generally unaffected by changes in coral cover. This study stresses the need for more detailed research in light of current and predicted declines in coral cover to elucidate specific differences in the dietary composition of C. auriga versus C. vagabundus, and the extent to which their prey is actually reliant on live coral.