Behavior of the Intertidal Gastropod Planaxis sulcatus (Cerithiacea: Planaxidae) in Fiji: Are Responses to Damaged Conspecifics and Predators More Pronounced on Tropical Versus Temperate Shores

Abstract

The intertidal herbivorous snail Planaxis sulcatus (Born) showed different avoidance behavior in response to crushed conspecifics than that to whole or crushed Morula anaxeres (Kiener). Addition of a crushed conspecific to pools containing P. sulcatus caused most individuals to move until they had reached crevices, but addition of the predatory gastropod M. anaxeres caused most P. sulcatus to move upward until they were no longer submerged. Planaxis sulcatus that had moved to crevices in response to crushed conspecifics climbed upward until no longer submerged after M. anaxeres was added to pools. It is suggested that crushed conspecifics are a cue for shell-crushing predators, which may be escaped by moving to crevices. However, such behavior provides little or no protection against a drilling gastropod compared with climbing upward until no longer submerged. The rapid and almost unanimous avoidance response of P. sulcatus was contrasted with the less uniform and relatively slower responses of two temperate species, Littorina unifasciata Philippi and Littorina cincta Quoy & Gaimard, to their local predators. It is suggested that differences in avoidance behavior may indicate increased predation pressure at lower latitudes.