EFFECTS OF FLOW ON COMPETITIVE SUPERIORITY IN SCLERACTINIAN CORALS

An effective attack by a scleractinian coral on a subordinate neighbor typically results in the death of the subordinate's margin along the intercoral gap. We tested the assumption that spatial variations obser ved for interactions between a highly ''aggressive'' coral, Galaxea fa scicularis (Linne) and its subordinate neighbors can be partly explain ed by hydrodynamic conditions. For several months, we used submerged p umps to expose transplanted corals in situ to intermittently enhanced flow. This manipulation rendered aggression by G. fascicularis ineffec tive. Strong currents deflect the aggressor's tentacles and possibly e nhance the rate of tissue recovery in subordinate corals. Observations of naturally occurring pairs of G. fascicularis and subordinate neigh bors indicated that the proportion of cases in which the subordinate n eighbor exhibited damaged margins was significantly lower at sites exp osed to strong currents compared with protected reefs. If other aggres sive corals are similarly affected by flow, then at nondisturbed reefs , corals using aggressive strategies should have an advantage at sites characterized by weak flow, whereas fast-growing corals that compete by overtopping their neighbors should be superior at exposed sites. Th ese conclusions agree with observations that the abundance of G. fasci cularis and the percentage of unoccupied substratum are lower at the e xposed sites.