Foraging Behavior of Two Caribbean Chaetodontids: Chaetodon capistratus and C. aculeatus

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Abstract
Chaetodon capistratus is a browser on anthozoans, preferring hexacorals (scleractinians, anemones and zoantharians) over octocorals and antipatharians. Within its preferred group of prey, C. capistratus is an active generalist, taking more of a certain prey than expected when the prey is scarce and less than expected when the same prey is common. This foraging for evenness among items in the diet results in the diet being more diverse than the available prey. The local abundance of C. capistratus is significantly correlated with local coral surface cover and/or with local coral diversity, perhaps because C. capistratus forages for evenness of diet. The abundance of Chaetodon (Prognathodes) aculeatus, a predator, does not correlate with these aspects of coral cover. C. aculeatus preys upon small discrete items (polychaetes, crustaceans, eggs), probably more calorific than anthozoans. C. aculeatus is considered very selective not only because its prey occupy small areas, but also because these prey are effectively defended (e.g., eggs) or have effective predator avoidance mechanisms (e.g., tubeworms). C. capistratus bit prey more frequently and regularly over the exposed corals (29.4 ± 8.4 bites per 5-min period) than did C. aculeatus, which bit in spurts (12.2 ± 4.6 bites per 5-min period) when it found hidden items of higher caloric value than anthozoans. C. aculeatus spent a greater proportion of time searching for fewer items of higher caloric value. Coral tissue is abundantly available throughout the year on coral reefs, and the process of using it as a major source of food energy provides additional feeding niches, thereby contributing to the potential diversity of coral reef fishes and the carrying capacity for fishes by the coral reef habitats. Coral tissue appears to be an adequate source of food energy by its abundance, but chaetodontids tend to feed on a variety of scleractinians and must still occasionally obtain a few worms, crustaceans or fish eggs to augment this diet with essential nutrients. Although C. capistratus and C. aculeatus obtain most of their food energy from different sources, both may be limited in growth or reproduction by the same essential nutrients.

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