Drought events will become more frequent due the climate change. In floodplains, periphytic algae are responsible for part of the primary production, are the principal source of organic carbon deposition, play an important role in mineralization and nutrient cycling, and are the base of the food web for many organisms. As algae distribution in aquatic environments is a strong indicator of physical and chemical conditions of the sites, we aimed to determine the structure of periphytic algae in lentic and lotic environments during drought conditions and to uncover the main local abiotic factors in community structuring. We hypothesized diatoms would be more frequent than green algae and desmids at both sites, due to their resistance characteristics, and that higher periphyton algal richness, density and diversity would occur in the lake due to the greater availability of nutrients and the absence of flow. The study was carried out in the Finado Raimundo lake and the Ivinhema river in the Upper Paraná river floodplain during the low water period of 2011. Petioles of the aquatic macrophyte Eichhornia azurea (Sw.) Kunth were used as a substrate for periphytic algae. We found a total of 171 species, 104 species in the lake and 80 in the river. Diatoms were predominant at both sites due to their strategic traits, and between sites, there were different patterns in the periphytic algal community structure, owing to the distinctive physical and chemical characteristics of the lake and the river. Achnanthidium minutissimum (Kützing) Czarnecki and Nitzschia palea (Kützing) W. Smith were the most abundant species in both environments. Our results showed patterns of periphytic algae in a floodplain during drought conditions, which will assist in understanding their structuring during future drought scenarios.

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A taxonomic study of species of the genus Gomphonema Ehrenberg (Bacillariophyceae) was performed in alotic environment (Ipoitã Channel) of the Upper Paraná River Floodplain. Samplings were performed in June, September and December 2013 and February 2014. Two petioles of Eichhornia azurea (Sw) Kunth were sampled at three different sites in the channel. Twelve species and two taxonomic varieties were identified. All species identified were recorded at the sampling site 3, loca ated close to the Ivinhema River. The lowest number of taxa occurred at the sampling site 1 (9 specific and infra specific taxa), in the confluence with the Paraná River. All taxa of Gomphonema were the first record for the Upper Paraná River Floodplain. Our results emphasize the lack of taxonomic studies for the region and the importance thereof to the knowledge of biodiversity.

We aimed to evaluate the structure of periphytic algae communities, the trait distribution and the patterns of functional diversity in the last non-dammed stretch of the Upper Paraná River floodplain. We hypothesize that there is an increase in the functional diversity and a change of the traits and environmental variables structure along this floodplain. We expected an increase in the functional diversity due to the increase in tributaries propagule input leading to a functional divergence, provided by deterministic processes. The sampling was in channels, lakes and rivers in a floodplain area covering 230 km of extension of the main river. The periphyton was obtained from scraping petioles of the floating macrophyte Eichhornia azurea (Sw.) Kunth. The traits evaluated were life form and strength and form of adherence to the substrate. The functional diversity was calculated from a functional dendrogram and assembly rules. The hypotheses proposed in this study were partially accepted, since there was no increase in functional diversity along the sampled area, but we observed a change in the structure of the functional traits along the different stretches of the floodplain. The results showed diatoms as the dominant algae, and functional convergence as the assembly rule prevalent for this community. There was a large difference between local environmental factors along the floodplain. The protected areas housed the greatest functional diversity values, which was apparently influenced by the increase in functional diversity, which can be explained by the limnological factors and the input of propagules from the tributaries to the Paraná River. We noted the importance of the protected areas and local factors for assembly of this community.

The number of periphytic algae species in floodplain lakes is strongly related to the flood pulse. Necessarily, algae dynamics are linked to some hydrological attributes such as the frequency, duration and intensity of the pulse. We analysed the variation in richness of the periphytic algae community over eight years (2000-2007). Our aims were (1) to examine periphytic algae richness and its relationship with the pulse regime and (2) to verify temporal changes of this richness in response to frequency, amplitude and intensity attributes. We analysed the potamophase and limnophase periods over the years using the fFITRAS function. Simple regressions were performed to reveal the influence of hydrological attributes on the richness of the periphytic algal community. The hydrological regime presented wide hydrometric-level variation among years, and we verified the predominance of the limnophase periods. Periphytic algae richness was high (371 taxa), presented wide oscillations ranging from 68 to 169 among the years and showed a tight correlation with flood pulse intensity. Our results highlight that the hydrological regime was the main factor structuring the richness pattern of the periphytic algae community in a floodplain environment. Furthermore, the results showed that temporal variations of the periphytic algae richness were related to shifts in flood pulse intensity, suggesting that this attribute is a key factor for periphytic algae communities in the floodplain environment and is important to be considered in studies covering long time series.

In impacted floodplains, small tributaries have an essential role in the maintenance of ecosystem biodiversity. Aim: We aimed to characterise the periphytic diatom community (Bacillariophyta) in a protected area at the Upper Paraná River floodplain considering the importance of tributaries as a source of propagules. The purpose of this study was to understand the influence of the tributaries in the periphytic diatom community (Bacillariophyta) in a protected area at the Upper Paraná River floodplain. We expect that species present in the main river channel (mainly in the last stretch) would be a subset of the community present in the tributaries. Methods The study area is located in the last non-dammed stretch of the Paraná River in this floodplain, with the contribution of several tributaries. Sampling was performed in 2014 in two tributaries and three sites at the Paraná River main channel, and the periphytic material was obtained from petioles of the aquatic macrophyte Eichhornia azurea (Sw.) Kunth. Results We identified 115 diatom taxa. Higher values of species richness were registered in the tributaries, and higher densities in the tributaries and at sampling sites under the direct influence of the tributaries. We also observed a higher similarity between the tributaries, which are located in the preserved side of the floodplain. The results of beta diversity showed that closer sites had lower values, and that the species turnover was the component more important in this floodplain. Conclusion In this way, these results reinforce the importance of tributaries mainly on the algae establishment and development reflected in the density of species. It demonstrates that sites in preserved area present a higher species richness and can serve as a pool of propagules for downstream environments.

Aim A taxonomic study of the species of the genus Cosmarium Corda ex Ralfs (Desmidiaceae) was conducted in two lentic environments of the Upper Paraná River Floodplain (Garças and Patos lakes). Methods The samples were collected in November 2016. Two petioles of Eichhornia azurea (Sw) Kunth were sampled and analyzed qualitatively. Results Six species, nine varieties, and three forms were identified, with five taxa being common to both lakes, nine in Garças Lake, and four in Patos Lake. Of this, thirteen species represent the first records for the floodplain environment. Conclusion This study contributes to the knowledge of the biodiversity of this region, providing support for future ecological studies and biomonitoring.

Habitat complexity may stabilize consumer–resource interactions and reduce the probability of invasion in aquatic habitats. We tested the hypotheses that (i) higher habitat complexity reduces resource consumption independently of grazer species, but that (ii) invasive grazers have a greater influence on decreasing resources independently of habitat complexity. We performed an experiment using artificial substrates to simulate different complexity levels. We evaluated Melanoides tuberculata (O.F. Müller, 1774) and Aylacostoma chloroticum Hylton Scott, 1954 consumption of specific algal groups and the interaction between habitat complexity and grazer species. Moreover, we evaluated grazer activity on the different substrates during the experiment. The results support only the first hypothesis and indicate lower resource consumption on complex substrates compared with simpler substrates. Additionally, the effect of the grazing of the invasive species on taxon richness was greater in simplified than in complex habitats. The grazing activity on the substrate suggests a relationship between resource exploitation and habitat complexity in which the invasive grazing species visited the simple habitat less frequently. However, the effects of invasive grazers on food resources were higher on the simple substrate. The effects of grazing activity on food resources depend on the interaction between habitat complexity and grazer species. In this way, the introduction of an invasive species may have negative impacts on the structure and function of periphytic communities, mainly in simplified aquatic ecosystems.