Population Estimates of Hyalella curvispina Shoemaker (Amphipoda) in Aquatic Vegetation of
Northeastern Argentinian Ponds
GALASSI1, M.E., FRANCESCHINI1, 2, M.C. & NEIFF1,2, A.P.
1 Cátedra de Limnología. FACENA-UNNE; Av.Libertad, 5500; CP 3400.
2 CECOAL-CONICET; Ruta 5, Km 2,5 Corrientes; CP 3400.
ABSTRACT: Quantitative comparisons were made of the accuracy of different sampling nets (962 cm2, 707 cm2 and 380 cm2) and two techniques for extracting amphipods from plants. To test the spatial distribution of Hyalella curvispina, eight sites with different environmental conditions were sampled between October and December 1999. Temporal variations in abundance and biomass were quantified from January to December 1999 in one of these sites covered by Pistia stratiotes. Because smallest number of replicate samples for a given level of precision was required using a net of 962 cm2 and Berlese funnels, three replicate samples were taken each month with this sampling size and extraction techniques. High densities populations were found in permanent ponds with electrical conductivity between 65 and 260 mS.cm-1 and dominance of Pistia stratiotes. Multiple regression analysis revealed that population density in different pond of the Northeastern Argentinean was significantly related to conductivity and this variable explained 36 % of the variability in abundance. Mean monthly abundance of H. curvispina varied between 338 and 3200 per m2 and its biomass between 0.20 and 1.95 g.m-2. The population peak of H. curvispina occurred during October, in which there was no increase in plant biomass.
Key-words: Hyalella curvispina, aquatic macrophytes, subtropical wetlands.