Within-reef differences in diet and body condition of coral-feeding butterflyfishes (Chaetodontidae)

Given the highly stochastic nature of larval supply, coral reef fishes often settle in sub-optimal 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 baronessa and C. lunulatus) across contrasting habitats with markedly different prey availability. Despite differences in prey availability, densities of C. baronessa and C. lunulatus were 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. baronessa fed preferentially and almost exclusively on the coral Acropora hyacinthus. In contrast, in back-reef locations where coral prey was scarce and A. hyacinthus lacking, C. baronessa was much less selective and consumed a wider range of coral prey. C. lunulatus was less selective than C. baronessa, but the diet of C. lunulatus also differed significantly between habitats. C. lunulatus consumed mostly A. hyacinthus in front-reef locations but not in greater proportions than it was available. In back-reef locations, C. lunulatus preferentially consumed A. intermedia and Porites spp. The physiological condition of both C. baronessa and C. lunulatus was 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.