Trade-offs for the butterflyfish, Chaetodon multicinctus, when feeding on coral prey infected with trematode metacercariae

Predators that feed on prey infected with larval parasites risk parasitic infection and the subsequent costs parasites extract from their hosts. It has been hypothesized that selection could favor predators that feed on infected prey if there were some benefit from feeding on such prey that outweighed the risk of and/or costs associated with parasitic infection. I tested this hypothesis using a parasite-host system involving the coral-feeding butterflyfish, Chaetodon multicinctus, which preferentially feeds on coral polyps infected with trematode metacercariae. Infected polyps appear as obvious, swollen nodules on the coral colony. Coral is a relatively energy-poor food source and so the choice made by C. multicinctus to feed on infected coral might represent a trade-off between benefits gained from feeding on infected prey and the risk of acquiring and/or the costs of harboring the parasite. The rate of establishment of the trematode within C. multicinctus was low, especially compared to the fish's rate of consumption of infected coral. The low intensity of trematode infection, in field-caught fish, suggests that parasite acquisition may not be increasing linearly through time. There was no measurable effect of parasitic infection on the body condition or liver energy reserves of fish. The swollen nature of infected polyps allowed fish to obtain more coral tissue per bite when feeding on infected compared to uninfected coral. It is suggested that the benefits gained from enhanced feeding offset the costs associated with infection and thus may help explain why C. multicinctus chooses to feed on infected coral.