Small-scale patterns of distribution and size-structure of the intertidal littorinid Littorina unifasciata (Gastropoda: Littorinidae) in New South Wales

Abstract

Within-shore and among-shore patterns of distribution, abundance and size structure of Littorina unifasciata Gray were identified on a number of shores in New South Wales. There was significant patchiness in distribution, abundance and size of L. unifasciata among patches of shore only a few metres apart, at different heights on the shore and from shore to shore. On a particular shore, the sizes of snails were strongly correlated with densities. In contrast, differences in densities at different heights from one shore to another were not correlated with mean size of snails. Density and size were each strongly correlated with the height on the shore at which snails were found. At any one height, differences in densities and size were also correlated with the distribution of particular microhabitat variables, such as the slope of the rock surface, the presence of pits and shallow pools and the presence of barnacles. Densities were also negatively correlated with densities of the large microalgae-grazing limpet Cellana tramoserica but were independent of other littorinids. A number of alternative models have been proposed to account for these patterns of distribution, abundance and size. Although processes that might account for these patterns were not investigated here, quantification of such patterns at a number of spatial scales is necessary before potential factors that might affect small-scale spatial variation in densities and sizes of L. unifasciata can be identified and investigated.