SPATIAL-DISTRIBUTION AND THE EFFECTS OF COMPETITION ON SOME TEMPERATE SCLERACTINIA AND CORALLIMORPHARIA

The impact of interference competition on coral community structure is poorly understood. On subtidal rocks in the northeastern Pacific, members of 3 scleractinian coral species (Astrangia lajollaensis, Balanophyllia elegans, Paracyathus stearnsii) and 1 corallimorpharian (Corynactis californica) were examined to determine whether competition exerts substantial influence over their abundance and distributional patterns. These anthozoans occupy > 50% cover on hard substrata, and exhibit characteristic patterns of spatial distribution, with vertical zonation and segregation among some species. They interact in an interspecific dominance hierarchy that lacks reversals, and is linear and consistent under laboratory and field conditions. Experiments demonstrated that a competitive dominant, C. californica, influences the abundance and population structure of a subordinate, B. elegans, by (1) reducing sexual reproductive output, (2) increasing larval mortality, (3) altering recruitment patterns. Field cross-transplants revealed that the dominant also affects vertical zonation of a competitive intermediate, A. lajollaensis, by killing polyps that occur near the tops of subtidal rocks. It is concluded that between-species competition, mediated in part by larval-adult interaction, strongly influences the structure of this temperate anthozoan assemblage.