Species inventory of aquatic macrophytes in the last undammed stretch of the Upper Paraná River , Brazil Inventário de espécies de macrófitas aquáticas no último trecho sem barragens do Alto Rio Paraná , Brasil

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.


Introduction
Species inventories represent a consistent and efficient method for obtaining basic information on species distributions.This kind of data has been continuously claimed as a basis for prioritizing conservation areas and directing conservation actions (Prance & Campbell, 1988;Raven & Wilson, 1992;Balmford & Gaston, 1999;Brooks et al., 2004).Information on species distribution provides valuable inputs for habitat relationship modeling and biodiversity monitoring, which serves many conservational purposes, such as sustaining native populations and regulating invasive species (Thomaz et al., 2004;Elith & Leathwick, 2009).Despite the importance of such species inventories, this type of information still lacks for many areas or has been poorly implemented with incomplete surveys.
Similar to many other groups, information on species distribution of aquatic macrophytes shows large geographical gaps (Chambers et al., 2008).This group of aquatic plants include 2,610 species, with great species richness and endemism rates in the Neotropics (Chambers et al., 2008), which coincides with scarce inventories and intense threats for aquatic biodiversity such as habitat degradation, invasive species, flow modification, water pollution, and others (Dudgeon et al., 2006).
River commonly present high water transparency, low P concentrations, and intermediate N concentrations (Rocha & Thomaz, 2004;Thomaz et al., 2004).More details on the abiotic aspects for the area can be found in Santana et al. (2017).
Macrophyte taxa were inventoried in 27 sampling stations, coinciding with the sampling sites presented for other taxonomic groups (see other publications in this special issue).The sampling stations were distributed among three categories of habitats: the main channel of the Upper Paraná River, tributary confluences (areas in the mouth of tributary rivers that reach the Upper Paraná River), and the floodplain lakes.Among the sample sites, 12 were established in the main channel of the Upper Paraná River and distributed along the study area.Along the same stretch, seven sampling stations were in tributary confluence areas of the rivers Paranapanema, Baia, Ivinheima, Ivaí, Amanbai, Iguatemi, and Piquiri.The other eight sampling sites were the floodplain lakes Garças, Xirica, Pombas, Ivaí, Saraiva, Pavão, Xambrê, and São João (Figure 1).
Field surveys were conducted in November 2013 and in May and November 2014.At each sampling site, we used a boat and recorded all macrophyte species that were visualized by one observer in a transect at the littoral zone (50-100 meters surveyed for 15-30 minutes).Submerged species were sampled with rakes.Over the whole sampling period, samples were taken by five different researchers with similar training.Taxa identification was supported by specialized literature (e.g., Kissman, 1997;Kissman & Groth, 1999;Kissman & Groth, 2000;Lorenzi, 2000;Pott & Pott, 2000).We also used specialized literature for classifying macrophytes according to their life form: amphibian (AN), emergent (EM), rooted floating-stemmed (RFS), rooted floating-leaved (RFL), free floating (FF), free submerged (FS), rooted submerged (RS), and epiphytic (EP) species (Pott & Pott, 2000).

Analyses
Species records on different sampling dates were combined for each sampling site.General descriptions for macrophyte taxonomic aspects and life forms were explored by frequency of species occurrence, number of species per taxonomic family, and number of species per life form.
To describe the pattern of species accumulation with increasing sampling effort, we used a species accumulation curve.The sample-based protocol was employed and the accumulation curve was constructed in the R environment, using the iNEXT package (Hsieh et al., 2016).
To summarize the variation in the composition of the macrophyte species, we used non-metric dimensional scaling (nMDS).We used presence and absence data to perform the ordination, and the configuration of sites in the multivariate space was obtained using the Sørensen index.The nMDS was performed in the R environment, using the vegan package (Oksanen et al., 2017).
In the main channel of the Upper Paraná River, E. azurea, E. crassipes, and Paspalum repens were the most frequent species (Figure 3B; Appendix 1).Among the rare species, we recorded the emergent species P. hydropiperoides, Pontederia cordata, and Rhynchosphora corimbosa (Appendix 1).These species were considered rare since they showed lower frequencies of occurrence in relation to the other sampled species.
A total of 71 macrophyte taxa, belonging to 35 families, were recorded (Appendix 1; Figure 4).The number of macrophyte species recorded increased rapidly with increasing sampling effort (solid line; Figure 4), but did not reach an asymptote (Figure 4).Extrapolations of species richness provided by the species accumulation curves (dashed line) indicated that additional macrophyte taxa could still be recorded with increasing sampling effort (Figure 4).
The composition of the macrophyte species community was summarized by the nMDS (ordination stress = 0.12; Figure 5).Species composition in sites of the Upper Paraná River was mostly influenced by the presence of Hydrilla verticillata (Figure 5A and B), while the floodplain lakes were mostly characterized by the presence of S. melaleuca, Panicum maximum, Thelypteris sp., Eleocharis geniculata, Cissus erosa, Caperonia castaneifolia, and P. punctatum  (Figure 5A and B).The tributaries shared species with both the Upper Paraná River and the floodplain lakes and were slightly influenced by the presence of U. mutica (Figure 5A and B).

Discussion
The taxa recorded in the different habitats of the last undammed stretch of the Upper Paraná River represent about 7% of the total species registered in the entire Neotropical region (about 984 species) (Chambers et al., 2008).However, although this is seemingly a low percentage of species, this number becomes more significant considering the relative small area where our study took place and the low taxonomic resolution of many taxa we recorded (22 out of 71 taxa were recorded at the genus level).In our survey, we recorded several species also found in other floodplains and wetlands in the Neotropical region (Pott & Pott, 2000;Bove & Paz, 2003;Catian et al., 2012).Compared to previous studies in the same area, we recorded more macrophyte taxa than, for example, Murphy et al. (2003) (28 taxa), Bini et al. (2001), andThomaz et al. (2009) (50 taxa each).However, we recorded fewer macrophyte taxa than Ferreira et al. (2011), which may be related to the differences in the sampling approaches of the two studies.Our surveys were conducted in the littoral zones by boat to minimize survey costs and to maximize the inventoried geographical range, while the surveys performed by Ferreira et al. (2011) were more limited in terms of geographical range, but included additional microhabitats, such as marshes and intermittently flooded areas.Our study, however, provides a contribution in terms of expanding the geographical information on macrophyte distribution in the area.
Considering our findings in terms of taxonomy, the families with the greatest number of species were Poaceae, Cyperaceae, and Polygonaceae (Figure 3A).Both Poaceae and Cyperaceae are families with a cosmopolitan distribution, showing a great number of species.These species are most commonly associated with vegetation in poorly drained conditions such as swamps, marshes, bogs, and waterbody shores (Judd et al., 2009), but can also grow prolifically in areas with a shallow water column, such as littoral zones (e.g., Panicum pernambucensis).Species of these families usually have fast growth rates with propagule dispersion by water and wind, which enables them to achieve broader geographical distributions (Kissman, 1997;Matias et al., 2003).In addition, Poaceae and Cyperaceae hold species that are stoloniferous, a trait that makes them much more likely to expand their  distribution and to show dominant distribution in contrast to species from other taxonomic families.
Interestingly, within families with the greatest number of species, we recorded U. arrecta, which is a highly invasive Poaceae species native to Africa.This species has been recorded in several habitats of the Upper Paraná River basin (Michelan et al., 2010(Michelan et al., , 2013)), and records of its occurrence in the floodplain rise concerns.Even though the frequency of occurrence of this species was not remarkable, we believe that monitoring and management actions should be implemented as safety measures to avoid its potential spread and establishment in new sites.
Regarding the macrophyte life forms, emergent species attained the highest number of species recorded and were mostly represented by species of the Cyperaceae, Fabaceae, and Onagraceae families.These families are also present in other important wetlands similar to the one investigated here, such as the Pantanal (Pott & Pott, 2000).Emergent species usually have a higher tolerance to water stress and may easily adapt to intermittent conditions of flood and drought found in floodplain ecosystems.In our study, these species were recorded in all three habitat types (Upper Paraná River, tributary confluences, and floodplain lakes), which corroborates the findings from previous studies (Murphy et al., 2003;Santos & Thomaz, 2007;Pott et al., 2011;Tabosa et al., 2012).Most frequent among species with this life form was Ludwigia sp., which was recorded in all sampled ecosystems, but had a remarkable occurrence in lakes (Figure 5).Such findings were expected, given the great adaptability of this genus to different conditions.
The second most frequent life form was that of amphibian plants.This group has a stronger water stress tolerance than emergent plants and can occur in both drier and humid substrates (Matias et al., 2003).However, emergent life forms tend to be better competitors than amphibian ones due to their faster growth rates and opportunistic behavior (Lycarião & Dantas, 2017), which might explain the pattern found here.
The other two representative life forms were free-floating and rooted submerged macrophytes.These groups have, compared to the other life forms, a low diversity in floodplains (e.g., Junk & Piedade, 1997;Pott & Pott, 2000).In the sampled region, free-floating macrophytes were mainly represented by E. crassipes and S. auriculata, demonstrating a high frequency in all studied environments (Figure 5).These plants are highly spread in Neotropics and may achieve high abundances.
In the Amazon floodplains, for example, E. crassipes may build up 40 to 50% of total plants biomass (Piedade et al., 2010).Among the submerged macrophytes, the native Egeria najas and the exotic invasive H. verticillata were the most important in terms of frequency of occurrence, which corroborate the surveys performed by Sousa et al. (2009Sousa et al. ( , 2010)).Our results show that Egeria najas and H. verticillata differ in terms of colonizing habitats, with greater occurrence of Egeria najas in lentic habitats and greater occurrence of H. verticillata in the main channel of Upper Paraná River (also similar to Sousa et al. 2009Sousa et al. , 2010)).Such aspect was also important for distinguishing species composition between types of habitat.For example, the nMDS identified H. verticillata as one of the main determinants of the community composition found in habitats in the main channel of the Upper Paraná River (see Figure 5).
Considering the occurrences of species, regardless of their family or life form, the most frequent ones were Ludwigia sp., E. azurea, E. crassipes, P. ferrugineum, and S. auriculata (Figure 3), and this pattern was consistent across all types of studied ecosystems.All five species were found in at least half of the sampled Upper Paraná River areas.All of them are widely distributed in South American floodplains (Pott & Pott, 2000;Bove & Paz, 2003;Catian et al., 2012), and some of them are even found invading other continents and causing economic and ecological losses (Téllez et al., 2008).In accordance to their large geographical distribution and successful invasion of ecosystems in other continents, the great frequencies of occurrence of these species in our samples are most likely related to the great phenotypic plasticity they present (Wells & Pigliucci, 2000).
Contrasting the patterns for frequent species, many species recorded in our study can be considered rare due to their low frequency of occurrence (Figure 3).Among them, for example, are Hymenachne amplexicaulis, U. mutica, and Panicum maximum (Appendix 1), which were restricted to only one of the types of ecosystems investigated.Along with limiting environmental conditions, another possible explanation for the low occurrence of these macrophyte species is the presence of stronger competitors, hampering their establishment.
Here, we recorded occurrence of macrophytes species within the whole last undammed stretch of the Upper Paraná River.Such information mainly contributes to expand the recorded distribution of macrophyte species within this area, which may be particularly useful for conservation and management purposes.The relatively high diversity of macrophytes we found rises attention to the need of strengthening conservation measures in order to protect macrophyte diversity.In addition, our samples revealed broad spatial distribution of invasive species, such as H. verticillata and U. arrecta, which alarm for urgent monitoring of potential impacts.Lastly, we recommend future investigations to explore the relationships between distribution of macrophyte species with environmental factors in order to provide even more solid basis for macrophyte conservation measures.

Figure 3 .
Figure 3.Most frequent species found in all sampling sites (A) and in the different types of habitats sampled, including the main channel of the Upper Paraná River (B), the tributary confluences (C), and the floodplain lakes (D).

Figure 2 .
Figure 2. Number of species per family for families with the largest number of recorded species (A) and number of species per life form (B) across all sampling sites.

Figure 5 .
Figure 5. Non-metric dimensional scale (nMDS) for macrophyte species sampled at sites in the main channel (black), tributaries (dark gray), and floodplain lakes (light gray) of the Upper Paraná River.Both sites (A) and species scores (B) are shown.

Figure 4 .
Figure 4. Species accumulation curve for macrophyte samples conducted at the last undammed stretch of the Upper Paraná River.