CONICET | Buscador de Institutos y Recursos Humanos

Spatial distribution of Limnoperna fortunei larvae in the Middle Paraná River floodplain and its relative importance in the zooplankton were studied in 29 environments with different hydrological connectivity degrees. Two samplings were conducted during a low-water period. Four type of environment were studied: the main channel Paraná River and large secondary channels (MC), minor secondary channels (SC), connected lakes (CL) and isolated lakes (IL). In each environment, several physical and chemical parameters were measured. In situ, 30 to 140 liters of water were sampled and zooplankton were filtered through a 50-µm plankton net. Zooplankton samples were analyzed under binocular microscope (Rotifera, Claocera, Copepoda and L. fortunei larvae).In both sampling, larval densities ranged between 0.9 and 48 ind/L. No larvae were registered in IL. Abundance was slightly higher in MC and SC than in CL but the relative importance of larvae in the zooplankton was higher in MC than SC and CL. The straight-hinged stage concentration was higher in IL than in lotic environment, while umboned stage showed an inverse pattern.The present study provides relevant information on the spatial larval abundances in the Paraná River floodplain whose data are very scarce. The density values coincide with those values reported during months of peak reproduction. While larvae concentrations were similar among the environments, the decreasing trend of its relative importance in the zooplankton is consistent from the MC to the floodplain. In addition, concentrations of each larval stage were very different among the environments suggesting different survival rate of the stages in the floodplain. During low-water period, when population of L. fortunei are vulnerable to desiccation, the repopulation and the recruitment events ofthe mussel in the floodplain can occur over a large area, including lakes with different connectivity and distance from channels which provide larvae.