Patterns of species richness in sandy beaches of South America
Species richness of the intertidal macroinfauna of exposed sandy beaches around South America is reviewed in relation to geographic location. This macroinfauna is dominated by cirolanid isopods (Excirolana), bivalves (Mesodesma and Donax) and opheliid and spionid polychaetes. In general, the upper shore of tropical and subtropical beaches is characterized by crabs (Ocypodidae), whereas on temperate beaches it is dominated by talitrid amphipods and cirolanid isopods. The middle shore is primarily occupied by cirolanids and bivalves, and hippid crabs, bivalves and amphipods dominate the lower beach. Generally, species richness increases from upper to lower beach levels. Studies carried out on exposed sandy beaches of south-central Chile (ca. 40°S) show that different beach states harbour differences in species richness, with the greatest species richness on dissipative beaches, and the least on beaches with reflective characteristics, a pattern also observed in Uruguay.