PRUDENT SESSILE FEEDING BY THE CORALLIVORE SNAIL CORALLIOPHILA VIOLACEA ON CORAL ENERGY SINKS

Convergence of form and function has accompanied the evolution of modu lar growth in terrestrial plants and colonial marine invertebrates. Pa rt of this convergence is related to the optimal exploitation of resou rces (space and light) and the ability to translocate energy products from sources to sink sites. Feeding on the energy pathways and energy sinks of terrestrial plants is a well-known phenomenon. Hermatypic cor als, the major organisms constructing tropical reef environments, cont ain photosynthetic algae (zooxanthellae), energetic products of which are translocated towards sink sites located at the corals' growing tip s and regenerating areas. Despite the plant-coral convergence in energ y pathways and sinks, there has been no evidence to date that coral en ergy sinks are exploited by coral predators. Gastropods of the genus C oralliophila are found feeding on coral margins, causing small and loc alized tissue damage. However, the ability of these snails to continue to feed without moving over a long period remains puzzling. Using a C -14 labelling technique, we found that colony margins of the stony cor al Porites function as major energy sinks. When snails inhabited these sites they incorporated significant amounts of C-14, indicating that they had fed on photosynthetic products translocated from the interior of the colony Furthermore, when snails aggregate in the interior of t he colony, thereby causing large surface injuries, they induce the dev elopment of significant new sink sites. This mode of prudent sessile f eeding maximizes the efficiency of energy exploitation by the predator y snail, while minimizing tissue damage to the coral. The fact that en ergy sink sites occur in many coral species suggests that the strategy of sink exploitation for nutrition could also occur in many other mar ine host-symbiont relationships.