PATTERNS OF SPECIES RICHNESS IN SANDY BEACHES OF SOUTH-AMERICA

Species richness of the interidal macroinfauna of exposed sandy beache s around South America is reviewed in relation to geographic location. This macroinfauna is dominated by cirolanid isopods (Excirolana), biv alves (Mesodesma and Donax) and opheliid and spionid polychaetes. In g eneral, the upper shore of tropical and subtropical beaches is charact erized by crabs (Ocypodidae), whereas on temperate beaches it is domin ated by talitrid amphipods and cirolanid isopods. The middle shore is primarily occupied by cirolanids and bivalves, and hippid crabs, bival ves and amphipods dominate the lower beach. Generally, species richnes s increases from upper to lower beach levels. Studies carried out on e xposed sandy beaches of south-central Chile (ca. 40-degrees-S) show th at different beach states harbour differences in species richness, wit h the greatest species richness on dissipative beaches, and the least on beaches with reflective characteristics, a pattern also observed in Uruguay.