Competitive interactions among tropical intertidal limpets

The keyhole limpet, Fissurella virescens Sowerby, and the pulmonate limpet, Siphonaria gigas Sowerby, are commonly found in intertidal rocky shores along the Pacific Coast of Costa Rica. They occur from mid-low to high intertidal levels and their abundances are inversely correlated. Fissurella virescens is more abundant in the mid intertidal zone, whereas Siphonaria gigas is more abundant in the high zone. A factorial experiment was conducted to determine the effects of density on survival and weight loss of each species in order to distinguish between the effects of intra- vs. interspecific competition. The experiment was carried out in the habitat of highest density of each species. Intraspecific competition was found to be important in regulating the population density of Fissurella. Intraspecific competition did not regulate population density of Siphonaria but caused a decrease in body weight at high densities. Interspecific competition between both species was weak.