Prey selection by coral-feeding butterflyfishes: strategies to maximize the profit

Abstract

Factors that structure preferences among food corals were examined for the obligate coral-feeding butterflyfish Chaetodon multicinctus. In the field, fish show a simple repetitious pattern of foraging composed of (1) pre-encounter search for coral colonies, and (2) post-encounter inspection/orientation, bite, and consumption of polyps. Rose coral, Pocillopora meandrina, and the massive coral, Porites lobata, were taken in higher proportions than their percentage substrate cover, while finger coral, Porites compressa, was taken in lower proportion. Paired presentations of coral colonies in the lab gave similar results: Poc. meandrina was preferred over Por. lobata which was preferred over Por. compressa. Poc. meandrina tissue had the highest energy content, lowest handling time, and highest profitability. Energy content did not differ among Porites tissues, but handling time was greater and more inspective eye movements were made while foraging on the branched finger coral, Por. compressa. Experimental manipulation of coral colony morphology indicate preferences among Porites are most likely structured by handling costs. Predictions of a simple prey-choice foraging model are supported in the C. multicinctus system if abundance of the branched coral Por. compressa is estimated as that available to fishes rather than percentage substrate cover. The relative size and abundance of stinging nematocysts are also consistent with observed foraging patterns in the field, but await immunological confirmation. Coral-feeding butterflyfishes offer unique opportunities to test models of foraging ecology in reef fishes, and the direction of future studies is suggested.