The influences of physical factors on the distribution and zonation patterns of South African rocky-shore communities

Abstract

Vertical zonation and horizontal distribution patterns of both community biomass and species richness of rocky-shore marine invertebrates and algae are described at a broad geographic scale for seven West and seven South-East Coast intertidal rocky-shore communities situated between southern Namibia and KwaZulu-Natal, South Africa. There were consistent patterns for community biomass and species richness, both of which showed similar vertical and horizontal distributions in equivalent habitats, regardless of geographical location. This indicates that the processes which create these patterns operate and vary in a similar way, even between different geographical regions. Multivariate techniques were used to assess, at a local scale, the relative importance of wave energy, rock temperature and shore elevation on the structuring and spatial variability of community biomass. Direct gradient analyses revealed that wave action strongly influences the structure of mid- to low-shore communities, whereas the interaction between rock temperature and shore elevation (both of which influence desiccation potential) produces convergence of high-shore communities. There was a significantly positive relationship between wave action and the per-unit-area community biomass, and a negative relationship between shore elevation and biomass. The potential role that waves may play in determining overall intertidal productivity is discussed.