Influence of sea temperature, substratum and wave exposure on rocky intertidal communities: an analysis of faunal and floral biomass

Abstract

Effects of sea temperature regime, substratum type and degree of wave exposure on the composition of rocky intertidal communities in the Cape of Good Hope were examined using cluster analyses of data for biomass of 310 species on 12 rocky shores. The Cape of Good Hope forms an overlap area between the south and west coast intertidal biota of South Africa (Stephenson. 1939) and species composition was found to be largely influenced by temperature regime, species richness being greatest within the area of overlap. However, biomass is dominated by very few species, the 10 species with highest biomass on each beach accounting for an average of 92 % of total biornass. If the 10 species exhibiting greatest biornass on each of the 12 beaches considered are pooled, a total of only 45 species is involved; 25 of these reveal biomass trends in response to gradients of wave exposure. Thus, while temperature regime establishes, by exclusion, a framework of species composition on each beach, the actual biomass of the species present is largely influenced by degree of exposure. Cluster analyses based on biomass data reveal groupings based primarily on the degree of exposure and secondarily on temperature. While specific influences of substratum (especially of substratum instabil- ity) were apparent, any overall effects on the biota were masked by those of exposure and temperature.