Aquatic macrophyte traits and habitat utilization in the Upper Paraná River floodplain, Brazil

► Classification aquatic macrophyte assemblages. ► Use of a set of ordination techniques, coupled with fuzzy coding methods. ► In this study the main environment gradients were influenced by connectivity and stand size. ► The most important traits that discriminate species along these environmental gradients were size and morphology index. ► Azolla microphylla, Lemna minuta, Ricciocarpus natans and Wolffiella oblonga can be bioindicators of lakes connectivity. This study was carried out in the Upper Paraná River floodplain with the aim of classifying aquatic macrophyte assemblages and to find out whether species traits are related to habitat characteristics. We used fuzzy codification methods and ordination techniques to test our predictions. Samples were obtained quarterly from May 2000 to March 2002 in 7 lakes of different maximum depths, macrophyte stand sizes, shoreline slopes, and degrees of connectivity. The cover of each species was estimated according to the Domin-Krajina scale. The main environment gradients were influenced by connectivity and stand size. The most important traits that discriminated species along these environmental gradients were ‘size’ and ‘morphology index’, and to a lesser degree, ‘growth form’. There were four groups of aquatic plants sharing the same attributes. Groups 1 and 3 present the species of smaller size and less complex structure and groups 2 and 4 are groups of species of bigger size. Only the macrophyte group 3 responded similarly to the set of environmental variables, occurring in habitats with the same abiotic features. The other groups are be able to occupy different habitats with different abiotic features. The group 3 is found in connected lakes and may be indicators of lake connectivity. Salvinia spp. was the only free-floating species that occurred in disconnected lakes and did not share the same traits of the other free-floating macrophytes. This trait differentiation may be related to overcome other small free-floating species to colonize and persist in disconnected lakes. Our findings present one more step for driving future studies in these environments, presenting these macrophytes as bioindicators of connectivity.