Although episodic wetlands are very frequent environments in Argentina, the knowledge about their ecology is scarce. Thus, the aim of this study was to describe the diversity and changes in the horizontal distribution of crustaceans and rotifers in the episodic wetland El Guanaco, Province of La Pampa, Argentina, during the hydroperiod that took place between December 2003 and March 2004. After three years during which it was dry, torrential rains made it reach a depth of 0.42 m. After 48 hours, ovigerous females and males of Metacyclops mendocinus (Wierzejeski 1892), juveniles of Moina wierzejskii (Richard 1895), and larvae of Triops longicaudatus (LeConte 1846) were recorded. The conductivity was reduced, the ionic content was dominated by bicarbonates and sodium and the concentrations of nutrients were high. The samplings were carried out in three stations, which at first were in open waters. The stations presented a homogeneous horizontal distribution of microcrustaceans and rotifers, with a predominance of limnetic species. Later, two of the stations were surrounded by Eleocharis macrostachya Britton plants, which allowed us to determine changes in the taxonomic composition and the appearance of species associated with the presence of vegetation. We recorded 35 taxa, being Moina micrura Kurz 1874 constantly present and highest in numbers. Among rotifers, the genus Brachionus was the predominant one. The species richness was higher in the station which was covered by E. macrostachya plants. After a period of high temperatures, we observed that the richness and abundance of microcrustaceans decreased, whereas those of rotifers increased.
episodic wetland; rotifer and crustacean diversity; Triops; horizontal distribution; Argentine
