Aquatic habitats of the Upper Paraguay River-Floodplain-System and parts of the Pantanal (Brazil)

The Paraguay-Paraná river system forms an important ecological corridor across South America. Here, we report the first description of the fluvial geomorphology and the physical structure of aquatic habitats along the main channel a 200-km long section of the Upper Paraguay River between Cáceres city and Taiama island (Mato Grosso, Brazil). Four functional sets were identified: (a) main channel and anabranches, (b) floodplain channel, (c) floodplain lake, and (d) aquatic-terrestrialtransition zone. The diversity of functional units was higher in the meandering and transitional sectors (Brillouin index 1.957 and 2.003) than in the straight and fluviolacustrine sectors (Brillouin index 1.562 and 1.577, respectively). In the transversal dimension, the relatively homogeneous habitats of the main channel contrasted with the heterogeneous floodplain habitats. We attribute this morphological diversity to changes in the hydrological connectivity, caused e.g. by drifting large macrophyte mats or by multi-year periods of higher and lower inundation phases