Differing Competitive Hierarchies Between Scleractinian Corals on Natural Reefs and Recruits on Artificial Reefs

The dominance of any organism in a given habitat depends on its competitive ability. Competition among coral genera is an important factor determining the assemblage structure within reefs and other coral-dominated habitats. Here, we assessed the competition between scleractinian corals growing on natural and recruiting on artificial reefs. We evaluated different forms of direct-contact competition and investigated the variation among genera in their competitive abilities. We documented a total of 4151 interactions between 28 coral genera, with two-thirds of the interactions being between corals of the same genus. We found that the competitive ability of each genus was not necessarily related to the genus abundance. The genera Coelastrea, Dipsastraea, and Leptastrea were recorded as more competitive despite their sparser natural occurrence on the reef. Meanwhile, Lithophyllon and other Fungiidae corals were the most competitive genera. While Oulastrea was a competitive genus on the artificial reefs, it was the opposite on natural reefs. The greater competitive capacity of genera with relatively smaller colony sizes, like Oulastrea and Coelastrea, supports the hypothesis of a trade-off between aggression and growth. These findings are further discussed with regard to the possible influence of competition among recruits on the development of mature reef communities.