The importance of competition among small Agaricia in shallow Caribbean reefs and possible factors determining competitive outcome

Coral reefs provide habitats where space is limiting and competition for this resource plays a major role in shaping community structure. Competition among small corals may occur as coral larvae settle in aggregated patterns, creating space limitation. The coral Agaricia display aggregated patterns of settlement in cryptic habitats, which may lead to high levels of encounters among congeners early in life. The purpose of this study was to (1) estimate the importance of congeneric encounters in small Agaricia, (2) identify one factor that might intensify the frequency of encounters among them, and (3) address possible mechanisms responsible for competitive dominance in small Agaricia. Four mechanisms were addressed: Size asymmetry of competing colony, increase in tentacle length, growth rates and the ability to recognize or respond to competition by differences in nematocyst types. Results show that congene1ic encounters in Agaricia were predominantly at small colony sizes (:S: 4 cm). Topographic complexity is one factor intensifying the frequency of congeneric encounters, by increasing the density of larvae in cryptic habitats. Results investigating the mechanisms responsible for competitive dominance show that difference in colony size seem to play a role in congeneric competitive outcome in Agaricia. Moreover, the outcome of competition among small Agaricia demonstrate that dominance is associated with earlier tentacle behavior of contraction and expansion . In addition, dominant colon ies displays redirection of growth towards the site of interaction , whil e subordinate colonies grow faster away from competition. Together these results support the role of colony size, early tentacle behavior and redirection of growth in determining competitive dominance in small Agaricia. This study underscores the importance of competition among small corals where the outcome of such interactions may affect future coral population dynarrucs.