Abstract
The primary literature has generally overlooked sandy beaches as environments in which to test ecological theory. As a result, the variability among beach systems is often overlooked in assessments of coastal biodiversity. For example, in South Africa a comprehensive spatial biodiversity assessment (in 2004) identified five distinct marine bioregions along the coast of South Africa, but within this, beaches were aggregated and dismissed as 'sand'. The unstated assumption is that the spatial patterns exhibited by biological communities of beaches, and the ecosystem services that they provide, reflect those of other coastal habitats. Here we test this assumption by subjecting macroinfaunal community data from 113 intertidal beach transects to multivariate analysis and assess whether the five South African marine bioregions hold for sandy beaches. After filtering beaches with extreme morphodynamic states, two major bioregions were identified; these being the subtropical east coast (Kosi Bay to Port Edward) and south-west temperate coast (Sundays River to Grossebucht, Namibia). Between these bioregions, the Transkei Wild Coast emerges as a transition zone, although this was the least-sampled region, and greater sampling effort might reinforce its identity as a distinct bioregion. Significantly, the subtropical east-coast bioregion did not reflect the clear separation observed for intertidal rocky shores along this section of coast. By contrast, the south-west temperate bioregion did exhibit some division into warm-temperate (south-coast) and coldtemperate (west-coast) beaches. However, some of the high-diversity cold-temperate beaches from central Namibia grouped together with the south-coast warm-temperate beaches, which tended to have similarly high diversity. The most common taxa were high-shore crustaceans, with the species Excirolana natalensis occurring in 97 of the 113 beaches and Pontogeloides (Excirolana) latipes in 64 of the 113 beaches. The most abundant polychaete was Scolelepis squamata occurring on 55 of the beaches, whereas the most abundant molluscs, Donax serra and Bullia rhodostoma, occurred in 23 and 22 beaches, respectively. Sandy beach macrofaunal species therefore appear to be plastic in their long-shore distribution with very wide distributions. Ultimately, the four bioregions identified for beaches more closely reflect those for terrestrial than for marine communities, but with some peculiarities. This suggests that biotic patterns on sandy beaches differ from those on rocky shores and that these habitats therefore deserve their own focused studies in conservation initiatives.