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?!

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. THERE HAVE BEEN numerous reports of marine presence ofpredators. Rittschof(l980) showed invertebrates, especially gastropods, avoiding that hermit crabs are attracted by effluent species known to be predatory (e.g., Bullock from damaged conspecifics and argued that 1953, Feder 1963, Yarnall 1964, Edwards the benefit of acquiring a larger shell may 1969, Phillips 1975, 1976, Geller 1982, Pitcher outweigh the risk of predation while doing so, and Butler 1987). These reports have ranged and also presented evidence for a decision from observations of species moving rapidly between approach and avoidance that varies away or gyrating when touched by the predadepending upon the need for a new shell tor to controlled and replicated experiments (Rittschof et al. 1992). with quantitative data on rates of movement, We report on two responses by the interor the numbers in an area before and after tidal gastropod Planaxis sulcatus (Born) in addition of predators. Some invertebrates Fiji: crevice seeking in response to crushed also respond to the effluent from damaged conspecifics and climbing upward until no G0n-sJ'>~GifiGS-(Sn¥cter-l-96J-,-Hadlock-L980,-IQnger-submer-ged-in-r-esponse-to-the-pre I Parker & Shulman 1986, McKillup and tory gastropod Morula anaxeres (Kiener). McKillup 1992), and from these studies it has been suggested that for some species, effluent from crushed conspecifics is a cue for the MATERIALS AND METHODS Experiments were done during low tide in intertidal pools between mid tide level (MTL) and average high tide level on a rocky shore