Abstract: Zooplankton communities of hyposaline Pantanal lakes in Brazil

Zooplankton communities of hyposaline Pantanal lakes in Brazil W. M. Silva, K. F. Roche and O. Rocha Although the oeeurrenee ofhyposaline lakes is relatively rare in South Ameriea (ECHANIZ et al. 2006), they oeeur among the many lakes in the Nheeolandia region o f the Pantanal wetland. These water bodies have high eation eoneentrations, prineipally sodium and potassium, anions that include biearbonates, and they laek maerophytes and fish. Studies on the biotie eommunities of these lakes are searee; the diversity of the zooplankton has been found to be low when eompared with freshwater lakes (MÉDINA-JÚNIOR & RIETZLER 2005). We analyzed the zooplankton populations in 2 ofthese lakes; sampling was earried out in February 2005, at the en d o f the rainy season. Both lakes had high eonduetivities (mean values of 776 and 2659 JlS em-), high nutrient eoneentrations (mean values of590 and 999jlgP.L-), high ehlorophyll a eoneentrations (mean values of 55 and 52 jlg.L-), and high pH values (mean values of 9.2 and 9.5). The most abundant taxa reeorded were the eyclopoid Metacyclops mendocinus and rotifers Brachionus angularis and B. dimidiatus inermis, also found by GREEN & MENGESTOU (1991) in Afriean saline lakes. Up to 2300 ind.L-1 of B. angularis were found in the lake o f lower eonduetivity. Analyses of diurnal, seasonal, and inter-annual pattems o f ehange in the limnologieal eharaeteristies and plankton eommunities are ongoing, with the eventual aim of understanding the strueture and funetioning of these poorly studied systems.