SUN AND SHADE MEDIATE COMPETITION IN THE BARNACLESCHTHAMALUSANDSEMIBALANUS: A FIELD EXPERIMENT

Abstract

The barnacles Chthamalus fragilis and Semibalanus balanoides compete for space in the high intertidal zone in southern New England. Chthamalus settles throughout the intertidal and persists in the absence of competition with Semibalanus.Semibalanus also settles throughout the intertidal but is usually eliminated from the high intertidal zone by heat and/or desiccation. In a field experiment in the high intertidal zone, Semibalanus survived the high summer temperatures and overgrew Chthamalus under an opaque roof. Under a transparent roof and in control areas with no roof, Semibalanus died in mid summer, and Chthamalus persisted. Hence the intensity of interspecific competition is mediated by physical stress which primarily affects the dominant competitor.