Distribution patterns and selective feeding in two Astropecten species (Asteroidea:Echinodermata) from Cleveland Bay, northern Queensland

Abstract

During 1985, Astropecten zebra was concentrated in shallow inshore areas of Cleveland Bay, northern Queensland, Australia, whereas Astropecten velitaris was found only further offshore. The two species had an overlapping distribution in depths between 5 and 13 m, but juveniles (maximum arm length ≤ 16 mm) were virtually absent from areas of co-occurrence: A. zebra juveniles were largely restricted to inshore areas, whereas A. velitaris juveniles were predominantly found in offshore areas.

Analysis of stomach contents demonstrated that both species are selective feeders, consuming mainly bivalves and gastropods, which constituted nearly 90% of the diet in A. zebra and nearly 75% in A. velitaris. The diet of the latter is complemented largely by crustaceans (17.1%). Crustaceans were proportionately better represented in the stomach contents of A. velitaris than in bottom samples. In contrast, although foraminiferans and polychaetes dominated the bottom samples, they were virtually absent from the stomach contents of either species of Astropecten. Both species demonstrated a preference for small prey items. Although spatial differences in the diet of A. velitaris were observed, there was little evidence for competitive interactions.

The findings strengthen the view that there is a clear horizontal zonation in benthic communities of the Great Barrier Reef Marine Park, requiring an appropriate management strategy.