Sandy Beach Macrofauna of Eastern Australia: A Geographical Comparison

Abstract

Macrofaunal communities of sandy beaches in eastern Australia were investigated to ascertain the relationships between species number, abundance, biomass and diversity (Simpsons Index) and morphodynamic state (expressed as the dimensionless fall velocity (0) and Beach State Index (BSI)). Three biogeographical regions were chosen for comparison - "cool temperate" (10 beaches near Robe and Goolwa, South Australia), "warm temperate" (10 beaches near Coffs Harbour, New South Wales) and "tropical" (15 beaches near Mackay and Yeppoon, central Queensland). Cluster and ordination analysis showed each region to be biologically distinct in over 75% of the species. Each beach site was, as far as known, pollution and wrack free. Beaches were sampled once, at low tide, during mid-summer. A transect was drawn from high to low tide and three 33x33x35 cm samples taken from each of 10 equally spaced levels. Sediment samples at each beach level were also taken for granulometric analysis and wave height, timing and depth of the water table measured. Results show that macrofaunal species number (species richness), abundance and biomass each increase from a reflective to ultra-dissipative beach state - abundance and biomass increasing logarithmically. Within region regressions were not always significant; however this appears to be an artefact of the small range of BSI values available at each locale. Combined regressions for all beaches showed no relationship with 0; however, very significant trends were found for combined beaches against BSI, with over 65% of the variation in data points accounted for. Species number at warm temperate and tropical beaches was best described by a logarithmic model. Conversely, combined species number regressions were linearly related to morphodynamics. It is likely that, in reality, the combined regression is also logarithmic, with this trend confounded by under-sampling of the more dissipative beaches. Simpsons Index of diversity showed no relationship with morphodynamic state in any case.