Online first articles

Lateral hydrological connectivity can affect the community characteristics by promoting dispersal of organisms between the river and its floodplain. We investigated the species richness, specific diversity, and relative abundance of microcrustaceans transported by the flood and the macroinvertebrates retained by Pontederia crassipes Mart. roots in five floodplain lakes with different connectivity within the RAMSAR Site Humedales Chaco. Due to differences in the slopes of the floodplain studied, the connectivity was determined by the topographic location of each lake, rather than by the distance from the river. During the hydrological connection, there was a transverse gradient in the physical and chemical characteristics of the water, with an increase in the electrical conductivity and a decrease in dissolved oxygen and suspended solids in the more isolated sites. A total of 62 species of microcrustaceans (48 cladocerans and 14 copepods) and 63 taxa of macroinvertebrates were identified. The microcrustaceans had high species richness in the three most connected lakes, whereas the macroinvertebrates had a peak in taxa richness in the lakes with intermediate connectivity. The low beta diversity (βw) for both microcrustaceans (14.63 %) and macroinvertebrates (16.9 %) indicated that taxa richness varied little between sites with different hydrological connectivity. In both assemblages, cluster analysis based on the similarity of the relative abundance grouped the three sites more connected and separated from the less connected sites. Our results suggest that species richness followed different patterns in different assemblages across the lateral gradient and that the hydrological connectivity was more related to the relative abundance of microcrustaceans and macroinvertebrates than to the classical measures of βw. Species diversity indices did not vary between sites. The high total species richness of invertebrates is mainly a result of the spatial arrangement of the different floodplain lakes.