Linking hydrological connectivity and aquatic invertebrates richness and composition in the Paraná River floodplain

Hydrological connectivity and aquatic invertebrates across the Paraná River floodplain

Resumo

We investigated the species richness, specific diversity, and relative abundance of microcrustaceans transported by the flood and the macro-invertebrates retained by Pontederia crassipes Mart. roots in five lakes with different connectivity within the Ramsar Site Humedales Chaco. There was a transverse gradient in the physical and chemical characteristics of the water during the hydrological connection, with a decrease in dissolved oxygen and suspended solids in the more isolated sites. Beta diversity (βw) was estimated as an integrator of habitat heterogeneity. The connectivity of the lakes was defined by determining the date of first connection to the river in relation to the water level of the Corrientes gauge. A total of 62 species of microcrustaceans (50 cladocerans and 16 copepods) and 63 taxa of macroinvertebrates were identified. The microcrustaceans had peaks of species richness in more connected sites with direct connectivity, whereas the taxa richness of macroinvertebrates peaked at intermediate connectivity. The low βw for both microcrustaceans (14.63%) and macro-invertebrates (16.9%) indicated that taxa richness varied little between sites with different hydrological connectivity. The relative abundance of both assemblages, indicated by cluster analysis, was related to the connectivity gradient, reflected by the separation of the least connected sites from those most connected to the river. Seven species of cladocerans were found at all sites surveyed some of which are abundant in the Paraná River (Bosminopsis deitersi and Cerdiodaphnia dubia). The high total species richness of microcrustaceans and macro-invertebrates was mainly a result of the spatial arrangement of different floodplain lakes across the gradient of hydrological connectivity. The conservation of these vegetated wetlands requires the maintenance of effective widths of connectivity that provide diverse habitats over time.