Aim: The objective of this study was to evaluate the efficacy of phytoplankton functional groups as indicators of environmental conditions in floodplain rivers and lakes with different trophic state and connectivity degree to the Paraná River. Phytoplankton functional groups (FGs) cluster sensitive species to environmental variation and can be an alternative for environmental monitoring. Methods: Samples were performed quarterly from 2010 to 2013 in the Ivinhema, Paraná and Baia Rivers and in three lakes permanently connected to each river. Results: 419 taxa were identified, and those taxa that had values greater than 5% of the total biovolume were classified into FGs (P, C, A, B, MP, H1, W1, J, TD, L O , and N). The lakes presented higher biovolume and were more productive than rivers, especially in the dry periods. The rivers presented light limitation and low phytoplankton development. The FG L O was an indicator in rainy seasons. Both rivers and lakes were mostly oligotrophic. We registered FG indicators only for the lakes (A, B, C, E, L O , P, and W1) and mesotrophic environments (A, B, C, E, J, L O , and P). Conclusion: The FGs reflected the seasonal variation and the trophic state of environments in the upper Paraná River floodplain, mainly in the lentic environments. The species-environment relationship (FGs as indicators) was clearer in the lakes, probably because of the longer water retention that allows evidencing the response of the phytoplankton community to environmental factors. On the other hand, the absence of FGs as indicators in the rivers could be due to the high water flow that promotes dispersal stochasticity and masks the relationship between the environmental factors and the phytoplankton community. Thus, phytoplankton FGs proved to be a viable tool to evaluate the environmental conditions in a floodplain.
Limnoperna fortunei is an invasive mussel species that is continuously expanding through South American. It has five larval stages, which usually differ in tolerance to environmental factors. How different abiotic filters affect L. fortunei larval stages has not been studied in depth. We employed a detailed database describing five floodplain environments to investigate the distribution of L. fortunei larval stages within and among these environments and determine which local abiotic filters affect the density of each larval stage. We found that the two youngest larval stages accounted for up to 83% of the larval density in four of the five environments studied, confirming an expanding population pyramid of L. fortunei in these environments. We also found positive and negative relationships among abiotic filters, and these relationships affected, directly and indirectly, the density of the youngest larval stages. Turbidity, water level, and suspended inorganic matter directly decreased the density of the two youngest larval stages. Conversely, temperature and pH directly increased the density of D-shaped and umbonated stages, respectively. Additionally, water level indirectly increased the density of the youngest larval stages mediated by declines in turbidity and suspended inorganic matter. Our findings suggest a likely expansion of L. fortunei in the Upper Paraná Floodplain. However, local abiotic filters, such as turbidity, water level, and suspended inorganic matter, decrease the density of the youngest larval stages. This finding illustrates that the establishment of L. fortunei can be prevented mainly if the youngest larval stages are controlled.
Protection areas favor diversity as they decrease the impact of anthropic disturbance on biological communities. Testing its effects on diverse biological communities is a pivotal step to understand how different trophic levels react to such management and conservation strategies. Here, we used data collected from 1993 to 2018 from a subtropical floodplain to evaluate the effect of the installation of a protection zone on the taxonomic and functional diversity of the phytoplankton community. We showed that the installation of the park had a positive effect on the aquatic community, mainly related to the decrease of cyanobacteria dominance and to the increase of phytoplankton functional groups. However, our results also suggested that dynamics occurring in a scale beyond the park seemed to influence key factors for the phytoplankton community, such as transparency and nutrient concentrations. Thus, although we showed that a compensatory measure had a positive effect on biodiversity, we believe that the establishment of protection zones must also consider and integrate the management of the river basin where the areas to be protected are located.
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