Habitat Selection in Two Intertidal Snails, Genus Nerita

Adult Nerita versicolor and Nerita tessellata occupy higher and lower but overlapping zones of the rocky intertidal coast of the Florida Keys. Field and laboratory experiments suggest that the zonation is an active habitat selection based on responses to largely physical factors of light, water depth and slope. Both species are nocturnal, photonegative and are crevice dwellers. Both species migrate with the tide but N. versicolor retreats higher above the rising tide. Evidence for competitive exclusion is lacking but the zonation, though blurred at night when both species wander, does achieve some measure of resource partitioning.