Coral reef fishes use crown-of-thorns seastar as habitat
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Between January and July 2008, we observed an unusual association between several species of coral reef fishes and the corallivorous crown-of-thorns seastar Acanthaster planci within the lagoon of Moorea, French Polynesia (17°30′S: 149°50′W). Four species of recently settled damselfishes (Pomacentrus pavo, Dascyllus aruanus, D. flavicaudus, and D. trimaculatus) as well as juveniles and adults of a cardinalfish (Siphamia sp.) were seen sheltering within the venomous spines of Acanthaster. Three of the damselfish species normally occupy branching corals throughout their lives, one occupies sea anemones when young and shifts to general coral reef habitat when older, and the cardinalfish, an undescribed species (O. Gon and J. Randall, pers. comm.), appears to normally associate with sea urchins.
We know no prior records of damselfishes occupying Acanthaster. The outcome of this apparently short-term, opportunistic, commensal relationship is unclear. Only recently settled damselfishes were seen inhabiting Acanthaster, implying that individuals either move to more typical habitat after settling on Acanthaster, perhaps when seastars move near the reef, or die. In contrast, all life stages of the cardinalfish Siphamia sp., from recent settlers to adults mouthbrooding eggs were found on Acanthaster, as has been noted for other members of this genus (e.g., Allen 1972). These observations reveal previously unappreciated flexibility in the range of habitats used by several coral reef fishes. Future studies will be necessary to document whether this association persists beyond the current outbreak of Acanthaster and to determine the types and magnitude of potential effects on the population dynamics of the fish species involved.
We thank C. Lantz for assistance in the field, and three anonymous reviewers for helpful comments. Funding was provided by Northeastern University’s Three Seas Marine Biology program as well as the National Science Foundation (OCE 04-17412).