Community structure of periphytic Zygnematophyceae ( Streptophyta ) in urban eutrophic ponds from central Brazil ( Goiânia , GO ) Estrutura de comunidades de Zygnematophyceae ( Streptophyta ) perifíticas em lagos urbanos do Brasil central ( Goiânia , GO ) Francielle

Aim: This study aimed to investigate the community structure of Zygnematophyceae algae in the periphyton of nine shallow urban eutrophic ponds from central Brazil. Additionally, we compared two different substrates, hypothesizing that community structure attributes (chlorophyll a; Zygnematophyceae density, composition and richness) would differ between them. Methods: Samples were carried out in August 2014. Periphyton was collected from two different substrates, macrophyte (epiphyton) and rocks (epilithon). Results: The ponds presented pH ranging from neutral to slightly acidic and electrical conductivity in general higher than 60 μS.cm-1. Zygnematophyceae contributed with 0.82% of total periphyton community density in the epiphyton and 0.02% in the epilithon. Altogether 49 Zygnematophyceae taxa were recorded, distributed in 13 genera. Based on frequency of occurrence, most taxa were classified as rare, being present in less than 25% of the ponds. The taxa with higher densities were Cosmarium regnesii var. regnesii, Cosmarium abbreviatum var. minus, and Mougeotia sp. 3. When each pond was considered individually, other taxa were highlighted as the most abundant among Zygnematophyceae. It was the case of Staurastrum smithii, Cosmarium exiguum, Mougeotia sp. 1 and Mougeotia sp. 2. The two ponds with highest Zygnematophyceae density showed high similarity in the species composition (>70%); however, among the others, it was relatively low (<50%). Conclusions: The eutrophic ponds considered in this study presented high periphytic biomass, but with low Zygnematophyceae representativeness. The periphyton attributes were not significantly different between macrophytes and rocks. The substrate type was not a determinant factor for Zygnematophyceae periphytic algae in the studied ponds.

Information on Zygnematophyceae community structure in different environments, especially considering the trophic spectrum, can be useful as subsidies in the attempts to use these algae in biological typology.Proposals involving desmids as biological indicators date from last century (Coesel, 1975), and have considered community structure metrics such as species richness along with the occurrence of rare taxa and the presence of species that may be associated with ecosystem maturity (Coesel, 2001).
2001), once it allows the classification of different taxa as tolerant or sensitive to eutrophic conditions.Concerning periphyton community structure on different substrate types, comparative investigations have shown that its attributes may be influenced by natural versus artificial substrates (Cattaneo & Amireault, 1992;Albay & Akcaalan, 2003;Vadeboncoeur et al., 2006;Ferragut et al., 2010), macrophyte architecture (Cattaneo et al., 1998) and surface roughness (Sousa & Ferragut, 2012).Specifically, the few studies on Zygnematophyceae algae available in the literature, which are focused on macrophytes and/or sandy sediments (Pals et al., 2006;Mutinová et al., 2016), have suggested that substrate influence is relatively low and varies with sites.
The present study aimed to investigate the community structure of Zygnematophyceae algae in the periphyton of nine urban eutrophic ponds from central Brazil.Additionally, we compared two different substrates, macrophytes and rocks, hypothesizing that community structure attributes (chlorophyll a; Zygnematophyceae density, composition and richness) would differ between them.

Study area
This study was conducted in nine eutrophic ponds inserted in urban parks from the city of Goiânia (State of Goiás) (Figure 1).Their surface area ranges between 0.2 and 2.1 ha, with mean depth smaller than 2.3 m (Table 1).The urban parks present varied landscape composition, with native vegetation around springs and exotic and ornamental vegetation surrounding the ponds and recreational areas.The climate in the region is Aw according Köppen-Geiger classification, with a strong seasonality marked by a dry season from May to September and a wet season from October to April (Cardoso et al., 2014).Average annual temperature is 21.9 °C, with lower values between May and August and higher values in September; average annual precipitation is 1487.2mm.This climate is typical from the Cerrado phytogeographic Figure 1.Study area.Codes correspond to the nine ponds (see Table 1).Silva, F.K.L., Fonseca, B.M. and Felisberto, S.A. Acta Limnologica Brasiliensia, 2018, vol. 30, e206 domain, which predominates in the central Brazil (Bustamante et al., 2012).

Sampling
Samples were collected in August 2014, in the littoral zone.Each pond had three sampling sites.Periphyton was collected from two different substrates, macrophyte petiole (epiphyton) and rocks (epilithon).Among the nine ponds, only six presented both substrates, totalizing 45 sampling units (eight from epiphyton and seven from epilithon, each one with three replicates).The macrophytes sampled were all rooted emergent or submerged species.
The periphyton was removed from the substrate by scrapping with a razor blade (epiphyton) or by brushing (epilithon), using distilled water gentle jets.Samples were preserved with 0.5% acetic lugol solution and stored in the darkness.

Quantitative analysis
Periphytic algae were counted in random fields (Bicudo, 1990), using 2 mL chambers under inverted microscope (Olympus CKX41) at 400x magnification; sedimentation time followed Lund et al. (1958).For each sample, at least ten fields without new taxa were considered before stop counting.Density was calculated using the equation adapted from Ros (1979).

Data analysis
Multivariate descriptive analysis was carried out by applying principal component analysis (PCA) to the abiotic data (water temperature, pH, electrical conductivity, dissolved oxygen and turbidity) along with chlorophyll a and Zygnematophyceae density, using a covariance matrix with data transformed by ranging [(X -Xmin) / (Xmax -Xmin)].Differences between epiphyton and epilithon for the variables chlorophyll a, total density, Zygnematophyceae density and richness were evaluated using Mann-Whitney test.The relation between the variables total density, Zygnematophyceae density and chlorophyll a was separately tested by Spearman's Correlation (r s ), after data transformed by ln(x+1).Cluster analysis based on Simpson similarity index was performed with density data of Zygnematophyceae periphytic algae.It was followed by an Analysis of Similarity (ANOSIM) with data of Zygnematophyceae periphytic algae that contributed with more than 10% for at least one sample, using the same Simpson index, in order to test the hypothesis of differences between epiphyton and epilithon communities.The software PAST version 2.17c was used in these analyses  (Hammer et al., 2001).Results were considered significant when p < 0.05.

Results
The ponds presented pH ranging from neutral to slightly acidic and electrical conductivity in general higher than 60 µS cm -1 (Table 2).
Axis 1 and 2 of PCA explained 39 and 26% of data variability, respectively (Figure 2).The most important variables for Axis 1 ordination were Zygnematophyceae density (r = -0.64)and electrical conductivity (r = 0.63), whose vectors pointed to opposite directions.According to the graph (Figure 2), sites with lower Zygnematophyceae density (e.g., BF, LR, AR) were associated to relatively higher values of electrical conductivity, water temperature, chlorophyll a, turbidity and dissolved oxygen; all these variables were positively correlated to Axis 1.On the other hand, the ponds FL and LE were located at the negative side of the graph; the highest Zygnematophyceae densities were found in these sites (Table 3).Regarding the second axis, it suggested a primary production gradient, once variables directly related to photosynthesis (pH, DO and chlorophyll a) were the most important ones (r = 0.53, r = 0.52 and r = 0.45, respectively), positively associated to the majority of the ponds.
Chlorophyll a was positively and statistically correlated to total density (r s = 0.53; p < 0.001), although its correlation to Zygnematophyceae density was not significant (r s = 0.18; p = 0.22).Total and Zygnematophyceae densities were also positively and statistically correlated (r s = 0.69; p < 0.001).
Zygnematophyceae mean density was 6.10 3 ind cm -2 .It represented 0.82% of the total periphytic community in the epiphyton and 0.02% in the epilithon.When the substrates were compared, the community structure parameters did not present statistical differences (Figure 3).
Cyanobacteria was the group that contributed most to periphyton density (6.10 6 ind cm -2 ) especially in the epilithon, representing from 80 to almost 100% in some ponds.The class Bacillariophyceae had the second highest contribution, followed by Chlorophyceae (Figure 4).
Based on frequency of occurrence, most taxa were classified as rare, being present in less than 25% of the samples (Table 4).In general, the taxa with higher densities were Cosmarium regnesii var.regnesii, Cosmarium abbreviatum var.minus, and Mougeotia sp. 3. When each pond was considered individually, other taxa were highlighted as the most Table 3. Mean and standard deviations (n = 6, except at AR, BO and JB, where n = 3) values for periphyton community structure in nine urban eutrophic ponds from Goiânia, GO (see codes at Table 1).5).The Analysis of Similarity (ANOSIM) showed no statistical differences when Zygnematophyceae composition in the epilithon was compared to the one in the epiphyton (p = 0.18).According to cluster analysis (Figure 6), similarity among most ponds was around 50%.The ponds FL, AR and LE presented the highest similarities (> 75%), while BF pond was the less similar one (20%).
Total periphyton density in the urban ponds from Goiânia was relatively high as well.The results reported here were similar to the ones described for other Brazilian eutrophic urban lentic systems, with the predominance of Cyanobacteria, B a c i l l a r i o p h y c e a e a n d C h l o r o p h y c e a e (Borduqui et al., 2008;Cordeiro et al., 2017), and Zygnematophyceae contribution around 1%.In oligo-mesotrophic systems, such contribution has reached around 25% (França et al., 2011;Pellegrini & Ferragut, 2012;Souza & Ferragut, 2012;Santos & Ferragut, 2013;Camargo & Ferragut, 2014).Thus, similar to the chlorophyll a accumulation, the periphytic algae density was certainly associated with the high phosphorus availability in eutrophic ponds.In addition, the ponds' sediments release phosphorus to the water     column (Søndergaard et al., 2003), which may have favored the development of the periphyton on macrophytes and rocks, mainly due to the small depth of the ponds.None of the community structure parameters reported in the present study showed statistical differences between epiphyton and epilithon.Some authors have shown that other factors like spatial distance between localities and environmental variables may be more important for periphytic communities than the substrate itself (Pals et al., 2006).Concerning macrophytes, Mutinová et al. (2016) explored the role of combined effects of environmental factors and host specificity on epiphyton community structure and concluded that the influence of different macrophytes was site-specific; although some plant species such as the moss Sphagnum L. supported a remarkably different epiphytic community, most macrophytes showed a neutral effect.Mosses like Sphagnum were not among the substrates for periphyton in the studied urban eutrophic ponds.Our results suggest that the community structure of Zygnematophyceae algae was influenced by local features unrelated to substrate differences between macrophytes and rocks.Pals et al. (2006) and Mutinová et al. (2016) found relatively negligible effects of environmental factors, such as pH and conductivity, on algal community structure in oligo-mesotrophic environments from Europe.These variables are recognized as important driver factors on desmid communities (Gerrath, 2003).However, their influence is not so evident when ecosystems with the same trophic status are compared, especially in the oligo-mesotrophic zone of the trophic spectrum (Mutinová et al., 2016).In the present study, the first axis of PCA ordinated the two ponds with the highest Zygnematophyceae density (FL and LE ponds) in the opposite direction to the electrical conductivity vector, which agrees with the ecological preference of this algal group for waters with low conductivity (Gerrath, 2003).Considering the cluster analysis, FL and LE ponds were grouped with the highest species composition similarity (75%).The AR pond, although with a relatively high electrical conductivity and lower Zygnematophyceae richness, also presented high similarity with FL pond.It probably happened because the Simpson Index used in the analysis is independent of differences in local richness (Lopes et al., 2014), and the species present in AR pond were all in FL pond as well.
In summary, the nine eutrophic ponds considered in this study presented high periphytic biomass, but with low Zygnematophyceae representativeness in both epiphyton and epilithon.The periphyton attributes (chlorophyll a; Zygnematophyceae density, composition and richness) were not Acta Limnologica Brasiliensia, 2018, vol. 30, e206 significantly different between macrophytes and rocks.We concluded that substrate type was not a determinant factor for Zygnematophyceae periphytic algae in the studied ponds.

Figure 3 .
Figure 3. Box-plots of chlorophyll a (A), total density (B), Zygnematophyceae density (C) and Zygnematophyceae richness (D) in the epilithon and epiphyton of nine urban eutrophic ponds from Goiânia, GO.

Figure 6 .
Figure 6.Similarity of the epiphytic and epilithic algae composition (Simpson Index) in nine urban eutrophic ponds from Goiânia, GO.

Table 1 .
Geographic coordinates and morphometric data of nine urban eutrophic ponds from Goiânia, GO.
Figure5.Relative density (%) of the five most abundant taxa among periphytic Zygnematophyceae in nine urban eutrophic ponds from Goiânia, GO (see codes at Table1).