MEPS 221:125-133 (2001)  -  doi:10.3354/meps221125

ABSTRACT: Scleractinian corals may experience competition at early life history stages, particularly where aggregated settlement decreases the space available for growth. The outcome of such interactions can affect post recruitment success and the relative abundance of coral species. The purpose of this study was to determine the importance of competition among small colonies (≤4 cm diameter) of Agaricia on shallow (≤10 m depth) reefs in St. John (US Virgin Islands) and Jamaica. The association between the density of small Agaricia and the frequency of congeneric encounters was examined, together with the relationship between density of Agaricia and reef rugosity (topographic complexity). Rugosity was analyzed because it indirectly affects competitive interactions by providing cryptic habitats that promote aggregated settlement and coral-coral interactions. To test one possible mechanism determining the outcome of such interactions, the relationship between size asymmetry of competing colonies and competitive outcome was assessed. The results demonstrate that competition among small Agaricia is common, particularly where aggregated settlement is favored by high topographic complexity. In other words, competitive interactions among small Agaricia are affected by both physical (e.g., topographic complexity) and biological (e.g., settlement patterns) factors. The outcome of such interactions is influenced by the difference in size of competing colonies, with dominant colonies generally being larger than subordinate colonies. Further research is required to identify the mechanistic basis of dominance, but currently the most likely hypotheses are that large colonies are dominant because they have greater energy resources than small colonies, or intrinsically faster growth rates. The high frequency of competition among Agaricia colonies in St. John and Jamaica suggests that further studies of congeneric competition within the Scleractinia may prove valuable in understanding the population biology of this taxon.

KEY WORDS: Competition · Size asymmetry · Scleractinians · Small · Agaricia