Influence of coral symbionts on feeding preferences of crown-of-thorns starfish Acanthaster planci in the western Pacific

The crown-of-thorns starfish Acanthaster planci (L.) is well adapted to fee d on a wide range of different corals, but often exhibits striking preferen ce for a small suite of available prey species. Numerous theories have been forwarded to explain its feeding preferences, but many of these theories h ave not been tested. In this study, I test whether coral symbionts signific antly affect the feeding preferences of crown-of-thorns starfish by removin g symbionts from replicate colonies of 6 different coral species. Crown-of- thorns starfish had a clearly defined hierarchy of preference for the 6 dif ferent corals when these contained symbionts (Acropora gemmifera > A. nasut a = A. loirpes > Seriatopora hystrix > Pocillopora damicornis > Stylophora pistillata). However, when coral symbionts were removed, then the starfish readily consumed all 6 corals and did not exhibit any significant selectivi ty. Further manipulation of symbiont assemblages showed that the trapeziid crabs (Tetralia and Trapezia species) were the most effective of the variou s coral symbionts in deterring starfish from feeding on their host colony. Moreover, those corals that were least preferred by crown-of-thorns starfis h contained the largest and most powerful species of Trapezia (T. cymodoce) , whereas the most preferred corals contained only very small Tetralia spp. crabs. Further experimentation is required to assess the generality of the se results, but for the 6 coral species tested, it is clear that coral symb ionts land particularly trapeziid crabs) do have a marked influence on the feeding preferences of the crown-of-thorns starfish.