Main predictors of periphyton species richness depend on adherence strategy and cell size

<div><p>Periphytic algae are important components of aquatic ecosystems. However, the factors driving periphyton species richness variation remain largely unexplored. Here, we used data from a subtropical floodplain (Upper Paraná River floodplain, Brazil) to quantify the influence of environmental variables (total suspended matter, temperature, conductivity, nutrient concentrations, hydrology, phytoplankton biomass, phytoplankton species richness, aquatic macrophyte species richness and zooplankton density) on overall periphytic algal species richness and on the richness of different algal groups defined by morphological traits (cell size and adherence strategy). We expected that the coefficients of determination of the models estimated for different trait-based groups would be higher than the model coefficient of determination of the entire algal community. We also expected that the relative importance of explanatory variables in predicting species richness would differ among algal groups. The coefficient of determination for the model used to predict overall periphytic algal species richness was higher than the ones obtained for models used to predict the species richness of the different groups. Thus, our first prediction was not supported. Species richness of aquatic macrophytes was the main predictor of periphyton species richness of the entire community and a significant predictor of the species richness of small mobile, large mobile and small-loosely attached algae. Abiotic variables, phytoplankton species richness, chlorophyll-a concentration, and hydrology were also significant predictors, depending on the group. These results suggest that habitat heterogeneity (as proxied by aquatic macrophytes richness) is important for maintaining periphyton species richness in floodplain environments. However, other factors played a role, suggesting that the analysis of species richness of different trait-based groups unveils relationships that were not detectable when the entire community was analysed together.</p></div

Species inventory of aquatic macrophytes in the last undammed stretch of the Upper Paraná River, Brazil

<div><p> Abstract The last undammed stretch of the Upper Paraná River in the Brazilian territory is, to date, not completely inventoried, which rises concerns given the rapid rates of species extinctions. Aim Here, we provide an inventory of macrophyte taxa recorded in the last undammed 230 km stretch of the Upper Paraná River. Methods We inventoried macrophyte taxa in 27 sampling stations including lakes, the main channel of the river, and the tributary confluences in November 2013 and in May and November 2014. Macrophyte were sampled in littoral zones. We explored taxonomic and life form aspects of the recorded species. We used species accumulation curves and ordination techniques to summarize the variation in richness and composition of macrophyte species. Results We recorded 71 macrophyte taxa in 35 families. Most species were emergent, amphibian, free-floating, and rooted submerged. At the main channel of the Upper Paraná River, Eichhornia azurea, E. crassipes, and Paspalum repens represented the most frequent species. The most frequent species in the tributary confluences were Ludwigia sp., E. azurea, and Polygonum ferrugineum, while in lakes, Ludwigia sp., Oxycaryum cubense, and E. azurea were the most representative taxa. In regard to macrophyte composition, the invasive Hydrilla verticillata mostly influenced sites in the Upper Paraná River, in the ordination space, while floodplain lakes were mostly characterized by the presence of species such as Scleria melaleuca, Panicum maximum, and Thelypteris sp., among others. Conclusions Our study indicates that the last undammed stretch of the Upper Paraná River contains a large number of macrophyte species, suggesting that this stretch is an important area for the conservation of macrophyte species. In addition, the occurrence of invasive species (e.g., Hydrilla verticillata) within the investigated stretch deserves attention in terms of potential impacts for which management action may be necessary.</p></div

Intercept, partial regression coefficients (± SE)and associated <i>t</i>-tests for the species richness of small and large firmly attached algae regressed against our explanatory variables in the Upper Paraná River floodplain.

<p>Significant results are highlighted in bold.</p

Minimum (Min), maximum (Max), mean values and coefficients of variation of the limnological variables and of the phytoplankton, macrophyte and zooplankton datasets in environments of the Upper Paraná River floodplain (<i>n</i> = 30).

<p>The first five variables in this Table were summarized by a Principal Component Analysis (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0181720#sec008" target="_blank">Results</a> section).</p

Species richness variation of periphytic algae from the Upper Paraná River floodplain and of the groups formed according to morphological traits (<i>n</i> = 30).

<p>Species richness variation of periphytic algae from the Upper Paraná River floodplain and of the groups formed according to morphological traits (<i>n</i> = 30).</p

Intercept, partial regression coefficients (± SE) and associated <i>t</i>-tests for the species richness of small and large mobile algae regressed against our explanatory variables in the Upper Paraná River floodplain.

<p>Significant results are highlighted in bold.</p

Intercept, partial regression coefficients (± SE) and associated <i>t</i>-tests for periphytic species richness regressed against our explanatory variables in the Upper Paraná River floodplain.

<p>Significant results are highlighted in bold.</p