CONICET | Buscador de Institutos y Recursos Humanos

Abstract: The aim of the present study was to compare the abundance and species richness of zoo-heleoplankton bigger to 53 µm, in an annual cycle under similar climate conditions in three artificial ponds, in order to observe seasonal changes. Samples were taken from June 1993 to July 1994 in Corrientes, Argentine. The first pond (A) was covered a 80% by Eichhornia crassipes, the second one (B) with bloom of Microcystis aeruginosa and the last one (C) with organic matter deposited at the bottom. The water was more acidic at the pond A and contained more dissolved oxygen concentration at the pond B than at the other two ponds. The zoo-heleoplankton densities varied between 20-1728 ind.l-1 at pond A, 42-4082 ind.l-1 at pond B, and 148-2447 ind.l-1 at pond C. The maximun zoo-heleoplankton abundance was found in the pond with cyanobacteria bloom during Autumn 1994 and the minimum abundance was found in the one with predominance of E. crassipes. The rank of species richness was pond A > pond B > pond C. Rotifera was the most abundant group in the pond A whereas the larval stages of Copepoda were abundant in the other two ponds. Anuraeopsis navicula was the dominant population in the pond with macrophytes prevalence. Brachionus calyciflorus and larval stage of Copepoda had variable proportions in the pond with cyanobacteria bloom. Thermocyclops decipiens was the only present population in the pond with organic matter deposited at the bottom. Changes in species richness and low similarity of the zoo-heleoplankton between ponds were determined by differences in the quality of the water in relation to the presence of macrophytes, cyanobacteria, organic matter deposited at the bottom and fish predation. Multiple regression analysis (stepwise) revealed that the water transparency, dissolved oxygen and conductivity were the environmental variables that explain more than 42 % of variability in the abundance of the dominant species.