Interactions between Acanthaster planci (Echinodermata, Asteroidea) and Scleractinian Corals at Kona, Hawai'i

Abstract

Annual assessments of reef communities at Kona, Hawai'i, from 1985 to 1995 determined that the corallivorous sea star Acanthaster planci preferred as prey the smaller colonies of Pocillopora meandrina over the far more abundant Porites compressa and P. lobata. This finding came from three distinct settings: a Reef-Top habitat, where large (> 15 em) colonies of Pocillopora meandrina were dominant; a Reef-Face/Boulder habitat, where living scleractinians-mainly an encrusting form of Porites lobata-covered <5% of the substrate; and a CoralRich habitat, where living scleractinians-mainly Porites compressa and a massive form of P. lobata-covered >95% of the substrate. Although a corallivore, A. planci was most numerous on the reef face and adjacent boulders, where corals were fewest. There it fed mainly on colonies of P. meandrina, even though this species represented < 1% of the sparse coral coverage. Virtually all P. meandrina colonies in that habitat were < 10 em in diameter, and all seen eaten by A. planci there were <5 em. The sea star was less numerous where corals were most abundant, and there it fed on species essentially in accordance with their relative abundance in the environment. A strong inverse relationship in occurrence between the sea star and small P. meandrina colonies on the reef face and adjacent boulders indicated that this favored prey was a limited resource and that sea-star predation prevented it from becoming established in that habitat.