Patterns of species richness in sandy beaches of South America

ENGLISH ABSTRACT: Species richness of the intertidal macroinfauna of exposed sandy beaches around South America is reviewed inrelation to geographic location. This macroinfauna is dominated by cirolanid isopods (Excirotana), 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.4 0oS) 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 characteristic, a pattern aslo observed in Uruguay. *********** AFRIKAANSE OPSOMMING: Makroinfauna spesiesverskeidenheid van blootgestelde sandstrande van Suid Amerika word hersien en vergelyk ten opsigte van geografiese ligging. Die makroinfauna word oorheers deur lsopoda Cirolanidae (Excirolana), Bivalvia (Mesodesma en Donax) en Polychaeta Opheliidae en Spionidae. Oor die algemeen word die boonste deel van tropiese en subtropiese strande gekenmerk deur krappe (Ocypodidae) terwyl die gematigde strande oorheers word deur Amphipoda Talitridae en lsopoda Cirolanidae. Cirolanidae en Bivalvia word hoofsaaklik aangetref in die middelste gedeelte van die strand terwyl krappe (Hippidae), Bivalvia en Amphipoda die laer deel van die strand oorheers. Oor die algemeen neem verskeidenheid toe van die boonste na die laer dele van die strand. Studies wat gedoen is op blootgestelde strande in die suide van Chile (ca.40oS) het getoon dat verskillende strandstadia ooreenkom met verskille in spesieverskeidenheid met die hoogste spesieverskeidenheid op verstrooide strande en die laagste op reflektiewe strande. Hierdie patroon is ook waargeneem op sandstrande van Uruguay.