A comparison of intertidal assemblages on exposed and sheltered tropical and temperate rocky shores

Sheltered and exposed rocky shores were sampled on the Otago Peninsula (east coast of South Island, New Zealand) and Keppel Bay (northeast coast of Australia). There were no significant differences between these temperate and tropical shores in the following general features: species richness, Shannon diversity index, percentage cover of sessile animals, algae or bare space. Nor did the Shannon diversity index and percentage cover of algae differ between wave exposures, but species richness was greater on sheltered shores while the percentage cover of sessile animals and percentage of bare space were significantly greater on exposed shores. The density of oysters was significantly greater on tropical shores but did not differ between wave exposures. The density of barnacles was greater on exposed shores but not significantly different between tropical and temperate locations. The greatest density of macroinvertebrates, and of mussels, occurred on exposed temperate shores while the density of predatory gastropods was greatest on sheltered tropical shores. The density of grazing gastropods (not including littorinids) was not si,significantly different among categories of shores. When the relative abundances of ten guilds were analysed by nonparametric multivariate analysis, groups of shores representing each of the four categories of location and exposure differed significantly from each other. These results contradict some conclusions in the literature regarding the nature of tropical and temperate rocky intertidal assemblages. They also indicate that tropical communities are not necessarily more diverse than temperate ones.