Habitat diversity relative to wave action on rocky shores: implications for the selection of marine protected areas

1. Current selection of marine protected areas in South Africa is based on objective criteria including biogeographic representation and habitat heterogeneity. This paper specifically examines rocky shores on the west coast of South Africa to determine whether they are divisible into discrete 'habitats' that need independent conservation. 2. Seventeen rocky shores spanning the full spectrum of wave exposure were compared in terms of maximum wave forces, biomass, species richness and diversity among zones and sites. Three biotic assemblages were identified, characterizing sheltered, semi-exposed to exposed, and very exposed habitats. Differences among these were clear-cut low on the shore but disappeared at the top of the shore where wave action was attenuated and desiccation uniformly intense. 3. The recognition of three discrete biologically-defined habitats means that rocky shores cannot be regarded as a uniform habitat for conservation purposes. All three components need protection if the full spectrum of rocky-shore communities is to be conserved. 4. It is argued that this approach allows habitats to be defined in an objective manner, and that once this has been done, habitat heterogeneity constitutes a better measure of conservation value of an area than a 'hotspot' approach based on species richness and endemism. Copyright (C) 2008 John Wiley & Sons, Ltd.