Sandy Beach Community Structure: The Role of Exposure and Latitude

Data on structure of sandy beach communities in- cluding number of species, diversity, taxonomic compo- sition, density, and median grain size from 284 locations around the world were analysed to consider the effects of exposure and latitude. Number of species, H', density, and species richness increased with reduced exposure to wave action. The number of species per beach was highest for cold temperate beaches and decreased gradually towards the tropics, with high numbers in the tropics observed only on very protected beaches. There were no significant relation- ships between species richness, H', or density with latitude. The lack of an increase in diversity and species richness from the temperate zone to the tropics contrasts with the patterns shown for other habitats and other large species as- semblages. Two explanations are offered: the inadequate state of systematics and ecology of tropical taxa, and the physically stressful nature of the tropical intertidal habitat for marine invertebrates.