ROLE OF ASTEROID PREDATORS IN THE ORGANIZATION OF A SESSILE COMMUNITY ON PIER PILINGS

The diets of 4 species of asteroids were observed for `9 months on the piles of a pier at Rapid Bay, South Australia. Coscinasterias calamaria (Gray) fed on molluscs, crustaceans and moribund items. Patiriella brevispina H.L. Clark fed on compound ascidians, sponges and moribund items. Tosia australis Gray and Petricia vernicina (Lamarck) ate mainly sponges, bryozoans and compound ascidians. A short-term (6 months) caging experiment showed that 5 common species of sessile animals-3 sponges and 2 compound ascidians-were significantly reduced by seastar predation. Nevertheless, the amount eaten, considered with seastar densities and distributions, indicates that the seastars are unimportant in influencing the utilization of space by sessile fauna. From comparing caged and uncaged controls, we tentatively suggest that other predators are also unimportant, and that competition for substrate space and for access to the water column is (and, has been during the evolution of these sessile organisms) far more influential. © 1979 Springer-Verlag.