THE MORPHOLOGY OF THE SUB-LITTORAL GASTROPOD GIBBULA-CINERARIA (L) ALONG A GRADIENT OF WAVE ACTION

Exposure to wave action has been shown to influence the morphology of a number of intertidal gastropods. This study is concerned with the morphology of the sub-littoral gastropod Gibbula cineraria. Individuals were collected from sites adjacent to Lough Hyne in SW Ireland. Sites were located along a gradient of wave exposure ranging from a headland exposed to the Atlantic along the channel into the fully sheltered sea lough. Four shell characters, soft body weight and foot muscle weight were recorded for each individual. All the measured characteristics, except shell size, differed significantly (ANOVA) between sites. Between site 1, exposed to the Atlantic, and site 5 shell morphology and foot weight showed a graded variation which corresponded to the environmental cline in wave action. The highest relative foot weight, largest relative aperture size and shortest, broadest, shells occurred at the most exposed site. These patterns are in agreement with those observed in intertidal species. However, at the most sheltered sites these patterns break down, implying a response to other selective pressures - predation, food type. In view of the pelagic dispersal phase of G. cineraria these results imply the maintenance of a high degree of morphological plasticity.