Temporal and spatial variability in community structure of a sandy intertidal beach, Cape Paterson, Victoria, Australia

Abstract

The infauna of a sheltered sandy intertidal beach at Cape Paterson, Victoria, was sampled on a three-monthly basis over a two-year period. In total, 116495 individuals comprising 41 species were collected over this time. Common species collected included the dipteran Chaetocoelopa sydneyensis, the coleopteran Sphargeris physodes, the isopods Pseudolana concinna and Actaecia thomsoni, the amphipods Talorchestia cf. novaehollandiae and Exoediceroides maculosus, and the polychaetes Magelona sp. and Scolelepis lamellicincta. There were significant differences in infaunal densities and species richness between the beach heights sampled, with both factors increasing with decreasing beach height over the intertidal zone. In generaI, insects were confined to upper beach heights, polychaetes were confined to lower beach heights, and different crustacean species spanned the entire intertidal beach. Significant temporal differences also existed in infaunal densities and species numbers at most of the beach heights sampled. These temporal differences were related to changes in the densities of common intertidal species. Only four of these common species (S. physodes, C. sydneyensis, T. cf. novaehollandiae and E. maculosus) exhibited any seasonal pattern in this temporal variation in density. Multivariate analysis of infaunal data failed to consistently separate beach heights into the universal zones previously proposed for sandy intertidal habitats. The unpredictable nature of biotic and abiotic influences on sandy intertidal infauna makes it unrealistic to expect to be able to consistently separate faunal assemblages on any given sampling occasion, with the exception of a characteristic fauna with terrestrial affinities that is confined to the upper beach. Any zonation patterns identified as being present on sandy beaches need to be qualified by the time of year in which data were collected.