The swim response of the actinian Stomphia didemon to certain asteroids: distributional and phylogenetic implications

Abstract

Nine of 17 asteroid species in the Barkley Sound region of Vancouver Island cause the actinian Stomphia didemon to release its pedal disk and swim. Only the asteroid Dermasterias imbricata was identified as a predator of the anemone. In the laboratory two asteroid species interacted with S. didemon, including D. imbricata, which interacted with the anemone in the field. On rocky slopes, staged interactions with asteroids caused S. didemon to move to greater depths. This movement may contribute to the disproportionately low abundance of S. didemon in shallow water where asteroid abundance is high. That S. didemon shows the response to asteroid species that are not its predators may reflect phylogenetic affinities that exist between these asteroids and the predator D. imbricata.