Macrobenthic assemblage structure in a cool-temperate intertidal dwarf eelgrass bed in comparison with those from lower latitudes

The evolution and ecology of latitudinal patterns in marine macrofaunal biodiversity and assemblage structure are contentious. With the aim of investigating the occurrence of such patterns in intertidal dwarf eelgrass beds (Nanozostera spp.), those at cool-temperate Scolt Head Island, UK (latitude 52 degrees N), were examined and compared with equivalent systems in warm-temperate Knysna, South Africa (34 degrees S), and subtropical Moreton Bay, Australia (27 degrees S): systems that had earlier been examined using an identical methodology. The Scolt Head bed supported the highest faunal density (mean 6568 0.1 m(-2)), lowest observed and estimated species richness (32 and 33 spp., respectively), lowest species diversity (Simpson's index of diversity 0.34), highest mean constancy index (23.0), lowest proportion of total numbers contributed by singletons or doubletons (0.06%), largest Berger-Parker dominance index (0.81), and least degree of variability between component samples. The beds at Knysna were intermediate between those at Scolt Head and at Moreton Bay in all those respects, as well as in nature and composition of the fauna. Similar dwarf eelgrass beds at Arcachon, France, likewise appear intermediate between those of Scolt Head and Knysna. Community variance in all three regions was greatest at the smallest spatial scale of < 1 m, at which scale two of the three sites also displayed randomly organized faunal assemblages, although this changed to non-random at larger spatial scales. Assemblages were deterministically structured at all spatial scales at Knysna. A consistent series of changes in structural characteristics of macrofaunal dwarf-eelgrass assemblages therefore occurred along the latitudinal sequence of Scolt Head (53 degrees), Arcachon (45 degrees), Knysna (34 degrees), and Moreton Bay (27 degrees). Community assembly patterns did not change with latitude, however, but did so with spatial scale in two of the three regions. (C) 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 104, 527-540.