Taxonomy of common taxa of Chlorophyceae (Chlorophyta) and Zygnematophyceae (Streptophyta) from periphyton of a Neotropical floodplain

Some orders of algal groups such as Chlorophyceae and Zygnematophyceae have been reported as frequent taxa in periphytic communities of wetlands. The present study aimed at submitting these algal members which occurred in high abundance and frequency in the periphyton of 30 environments of the Upper Paraná River floodplain to a taxonomic survey and to present some ecological data concerning their richness. Periphyton were collected from petioles by scraping of Eichhornia azurea (Sw.) Kunth and preserved with Lugol acetic solution in the Upper Paraná River, Brazil, during high water period in March 2010. Taxa were counted in inverted microscope and those higher than 2,500 individuals in density with frequency of occurrence less than 50% simultaneously in the 30 environments sampled were subjected to a detailed taxonomical treatment under optical microscope coupled to a light camera and ocular micrometer under 1000x. Identifications and descriptions were made according to the algal literature. Some abiotic data were shown. Fifteen taxa belonging to the classes Chlorophyceae and Zygnematophyceae were abundant representing 64.6% of the total density. A Procruste analysis within a Detrended Correspondence Analysis showed that distribution pattern of richness of clorophyceans and zygnematophyceans was represented by common species of these communities, highlighting the importance of knowing about these algae taxonomy.


Introduction
Periphyton community displays high algal species richness and diversity (França, Lopes, & Ferragut, 2011). The morphological structure and the taxonomical diversity of the periphytic communities are strongly related to abiotic factors e.g., physical and chemical variables (Villeneuve, Montuelle, & Bouchez, 2010). In most cases this community can be regulated by a few species with high abundance and wide frequency of occurrence, thus playing an important ecological role (Gaston, 2011). Common species, unlike rare species, present a broad environmental range (i.g., generalists) and evaluation of parameters governing distribution of these common species may help the knowledge of the general patterns influencing the spatial variation of biodiversity (Tonial et al., 2012).
The Upper Paraná River floodplain is an important center of biological diversity in Brazil, where preservation and conservation are priorities for this wetland (Algarte, Siqueira, Murakami, & Rodrigues, 2009). In this context, taxonomic surveys of periphytic algal communities can provide valuable information and it is indispensable. Taxonomic data concerning description of periphytic taxa for the Upper Paraná River floodplain are only presented for Cyanobacteria (Fonseca & Rodrigues, 2005), for xanthophyceans and euglenoids (Biolo & Rodrigues, 2011a), for dominant algal species in an open lake (Biolo & Rodrigues, 2011b) and for a diatom genus, Gomphonema Ehrenberg (Osório, Tremarin, Ludwig, & Rodrigues, 2017).
Therefore, in the present study we aimed at carrying out a taxonomy treatment of chlorophyceans and desmids which occurred in high abundance and frequency in 30 environments of the Upper Paraná River floodplain. We also have shown some ecological data concerning how richness of those groups behaved in the periphytic community.

Material and methods
The Upper Paraná River floodplain in Brazil is located between Mato Grosso do Sul and Paraná States (22º40'-22º50'S and 53º10'-53º24'W). The study was conducted including 30 different environments of this floodplain: 12 areas belonging to the Ivinhema River subsystem; 12 areas of the Baía River subsystem; and six of the Paraná River subsystem ( Figure 1). Periphyton samples were collected at each sampling site during high water period in March 2010, the period of study which was chosen for sampling by the highest species richness of periphytic community according to earlier studies (Algarte et al., 2017b). Periphyton was removed from two petioles of the macrophyte Eichhornia azurea (Sw.) Kunth by scraping with a stainless-steel blade and jets of distilled water. Substrate is an abundant and persistent aquatic macrophyte in the studied environment and thus was chosen as the standard substrate for sampling. Periphytic material collected was placed in Wheaton flasks (150 mL) preserved with Lugol acetic solution (Bicudo & Menezes, 2017) and were deposited in the Acta Scientiarum. Biological Sciences, v. 42, e50099, 2020 Herbarium at the Universidade Estadual de Maringá (HUM) under the numbering registers 28702-28726.
Qualitative analysis of taxa was made under optical microscope coupled to a light camera and ocular micrometer under 1000x and identifications were made as possible at the lowest taxonomic level, according to the classical and regional literature (e.g., Croasdale & Flint, 1986, 1988Prescott, Croasdale, Vinyard, & Bicudo, 1980;Komárek & Fott, 1983;González, 1996;Domingues & Torgan, 2012;and others). Taxa higher than 2,500 individuals in density simultaneously with frequency of occurrence higher than 50% in the 30 environments were subjected to the taxonomical treatment.
To assess the level of whether the community of clorophyceans and zygnematophyceans can be represented by common species, it was verified the congruence between ordinations which were carried out with common taxa and total using the Procruste (Jackson, 1993;Peres-Neto & Jackson, 2001). We used the randomization procedure of Monte Carlo (9999 with randomization) to assess their validity. Results of the Procruste analysis (m2) were subjected to square root of their complements (r = √(1-m2) (Oksanen et al., 2011) and transformed in a correlation coefficient (r). Thereby values close to 1 indicate greater similarity between the patterns of order and values close to zero greater dissimilarity between these standards. A Detrended Correspondence Analysis (DCA) was applied to show how those results behaved in our study.

Results and discussion
It was recorded a total of 208 taxa belonging to Chlorophyceae and Zygnematophyceae in the 30 sampled environments at the Upper Paraná River floodplain. Fifteen taxa of this total were abundant and occurred widespread. These taxa represented 64.6% of the total density and were submitted to a taxonomical treatment, classified and described in the present study as follows: CHLOROPHYTA Class Chlorophyceae Order Chlorococcales Family Chlorellaceae Ankistrodesmus falcatus (Corda) Ralfs, Brit. Desm., 180, pl. 34, figures a-c. 1848. (Figure 2A) Colonies composed of 1-2 fascicles with 5 cells irregularly arranged, cells 2 times longer than wide, 13.9-17.8 μm long, 0.8-1 μm wide; long, fusiform, falcate cells, slightly arched, cells joined by contact of the convex middle region; single, parietal chloroplast without pyrenoid.
Notes: Our specimens presented cellular dimensions lower than those described by González (1996), but description of cell morphology agrees with that presented by Komárek and Fott (1983). Present taxon is common in calm waters with low concentration of nutrients, in phytoplankton and periphyton (Ramos, Bicudo, Góes Neto, & Moura, 2012).
Notes: A. fusiformis is related to A. spiralis which the first differs by its crossed disposition of cells instead of twisted cells in the second. Our populations agree with that presented by Komárek and Fott (1983). It is considered a cosmopolitan taxon in phytoplankton and periphyton (Ramos et al., 2012).
Notes: M. contortum is morphologically similar to M. irregulare (G.M. Smith) Komárková-Legnerová, but the first presented more sigmoid cells and larger cell dimensions. It is a cosmopolitan taxon, very common in waters with different trophic conditions (Ramos et al., 2012).
Notes: Differs from C. venus Kützing ex Ralfs by having more pronounced curvature of cell and acuminated poles (Oliveira, Bicudo, & Moura, 2013 Figure 2H) Small cells, about as long as broad, 10-10.5 μm long, 9-9.5 μm wide, deeply constricted at the middle, sinus narrow, linear and closed; transverse angular-oval semicells, lateral margin divergent, straight, to a rounded median angle, sometimes slightly pronounced, the upper margin almost straight, apex relatively broad, truncate; smooth cell wall, hyaline, axial, single chloroplast, with a single pyrenoid.
Notes: Present variety differs from the typical of species by its smaller dimensions, lateral angles less rounded and not pronounced (Felisberto & Rodrigues, 2010).
Notes: C. blyttii may exhibit polymorphism in semicells, especially with regard to the number of crenulations in lateral and apical margins and number of granules on the face of each semicell (Oliveira, Bicudo, & Moura, 2010).
Notes: This variety differs from typical to present the lateral margins of semicell never straight in the middle and apical margin relatively wide (Felisberto & Rodrigues, 2010). Although periphyton community displays high algal species richness and diversity (Biolo & Rodrigues, 2013;Algarte et al., 2017a), identifying the spatial (and also temporal) pattern in composition of periphytic algae is fundamental to the knowledge of its biodiversity (Svoboda, Kulichová, & St'astny, 2013). It is known that periphyton dynamics is related to climatic, hydrodynamic and abiotic variables (Larned, 2010). In our study, Cosmarium leave and C. abbreviatum were characteristic in environments with high conductivity and inorganic nitrogen contents related to the Paraná subsystem. Cosmarium regnesii, Staurastrum micron, Euastrum rectangulare, Ankistrodesmus fusiformis and Monoraphidium arcuatum occurred in deeper environments with higher temperatures and with higher levels of orthophosphate related subsystem Ivinhema. Closterium incurvum, Ankistrodemus falcatus and Monoraphidium contortum preferentially occurred in more transparent waters related to Baía subsystem. Other taxa occurred under wide environmental conditions. It was performed a DCA (Figure 4) with the frequent taxa of desmids and chlorococcaleans found in our study, to preview how data could behave, according to tendencies in current studies about investigations on partitioned richness. According to the result obtained by Procruste ordination based on data from common species, a high congruence with the ranking based on all taxa was shown (r = 0.71; p < 0.001). This indicates that the distribution pattern of clorophyceans and zygnematophyceans is represented by common species of these communities. Our results meet those reported by Lennon, Koleff, Greenwood, and Gaston (2004) with birds. According to them, low richness is better explained by common species than high richness by a group of rare species with the same size. By comparing the two algal groups -zygnematophyceans and chlorophyceans -worldwide, it was observed that desmids are better known in its distribution or occurrence than other green algae, mainly because of the difficulty to identify coccoid forms of chlorococcaleans (Coesel & Krienitz, 2008). In this way, we focused on the taxonomical recording of these two frequent groups in the Paraná River floodplain in the present study.

Conclusion
We encourage taxonomic researches for the knowledge of biodiversity of the neotropical areas and tendency of more studies concerning how the richness of individual groups combine to produce the overall variation that could be observed in nature, creating diversity patterns, using data about common species.