Abstract
Given the highly stochastic nature of larval supply, coral reef fishes often settle in suboptimal habitats with limited access to prey or other resources. Variation in the availability and quality of resources among different reef habitats is likely to have significant effects on the physiological condition and subsequent fitness of resident fishes, if not their absolute abundance. This study compared the abundance, feeding and condition of 2 species of coral-feeding butterflyfishes (Chaetodon baronessaandC. lunulatus) across contrasting habitats with markedly different prey availability. Despite differences in prey availability, densities ofC. baronessaandC. lunulatuswere very similar between locations. However, there was significant spatial variation in their feeding and physiological condition. In front-reef locations, where coral prey was highly abundant,C. baronessafed preferentially and almost exclusively on the coralAcropora hyacinthus. In contrast, in back-reef locations where coral prey was scarce andA. hyacinthuslacking,C. baronessawas much less selective and consumed a wider range of coral prey.C. lunulatuswas less selective thanC. baronessa, but the diet ofC. lunulatusalso differed significantly between habitats.C. lunulatusconsumed mostlyA. hyacinthusin front-reef locations but not in greater proportions than it was available. In back-reef locations,C. lunulatuspreferentially consumedA. intermediaandPoritesspp. The physiological condition of bothC. baronessaandC. lunulatuswas much worse in back-reef locations compared to front-reef locations, which may reflect differences in the quantity and/or quality of prey available in different habitats. This study suggests that small-scale (within-reef) differences in prey availability can have significant effects on the physiological condition and subsequent fitness of coral reef fishes.