Gomphonema Ehrenberg (Bacillariophyceae) in a lotic environment of the Upper Paraná River floodplain, Brazil

. 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.


Introduction
The Upper Paraná River floodplain is characterized by heterogeneous habitats that confer high biodiversity to this environment (Thomaz, Bini, & Bozelli, 2007, Agostinho, Pelicice, & Gomes, 2008).Periphytic algae are one of the aquatic communities found in this ecosystem, with a high proportion of diatoms (Bacillariophyceae), especially in lotic environments.These algae present morphological adaptations that favor their attachment to substrates (Wehr & Sheath, 2003).
The diatom genus Gomphonema Ehrenberg is well represented in aquatic environments, presenting high richness and abundance.Gomphonema species are characterized by cuneiform cells in girdle view and hetero polar cells in valve view (Round, Crawford, & Mann, 1990).They generally attach to solid substrates through mucilage pads or stalks, secreted from the apical pore field located at the valve basis (Tremarin, Ludwig, Bertolli, Faria, & Costin, 2009a).In addition, cells possess a single H-shaped plastid with a central pyrenoid (Cox, 1996, Round et al., 1990).Several Gomphonema species are cosmopolitan.However, the morphological variability of frustules makes the taxonomy of this genus difficult (Krammer & Lange-Bertalot, 1986, 1991).
Almost 22 species of Gomphonema have been recorded for aquatic environments in Paraná (Tremarin, Freire, Bertolli, & Ludwig, 2009b), and only four species for Mato Grosso do Sul.The present study is the first floristic survey of Gomphonema in the Paraná River floodplain, contributing to the knowledge and characterization of aquatic biodiversity in this region, including ecology and biomonitoring studies, for which the correct identification of taxa is essential.
The goal of the present study was to perform a taxonomic analysis of species of the genus Gomphonema in a lotic environment of the Upper Paraná River Floodplain, contributing to the knowledge regarding the distribution of these species.

Material and methods
The study site is the Ipoitã Channel (22° 50'S; 53° 33'W), located in the Upper Paraná River floodplain, which connects the Ivinhema and Paraná rivers, with an average depth of 3.2 m.Samples were taken at three different sampling sites in this channel: site 1 at the connection with the Paraná River, site 2 in the middle of the channel, and site 3 at the connection with the Ivinhema River (Figure 1).This channel is inserted in the state of Mato Grosso do Sul, although it is practically on the border with the state of Paraná.
The substrates used were petioles of Eichhornia azurea (Sw) Kunth in the adult stage (Schwarzbold, 1990), selected from banks of this macrophyte of similar shape and size and under similar environmental conditions.Collections were performed in June, September and December 2013, and in February 2014.Periphytic algae were collected from the sixth or seventh plant internode of submerged mature petioles of Eichhorniaazurea (Sw.) Kunthas recommended by Schwarzbold (1990).This macrophyte was selected to this research because it was the most abundant and is used as a standard plant for the PELD-Long Term Ecological Research.Two petioles were collected randomly at each site, placed in 150 mL Wheaton bottles, sprayed with distilled water, and kept in boxes with ice.The periphytic material was subsequently removed using stainless steel bladesw rapped inaluminum foil and jets of distilled water.
The resulting material was fixed in1:1 Transeau solution (Bicudo & Menezes, 2006).Part of the sample was oxidized with potassium permanganate and hydrochloric acid, according to Simonsen (1974) as modified by Moreira-Filho and Valente-Moreira (1981).Due to the high amount of organic matter in the blades, the material was oxidized again according to Hasle and Fryxell (1970).The resins used to mount permanent slides were Hyrax for the first method and Nafrax for the second.One slide was mounted per site sampled in certain periods, resulting in 12 slides, in total.These slides were not quantified, but all of them were analyzed for species richness.
Gomphonema species were analyzed using a binocular microscope with amicrometer ocular and 100x objective, and images were captured using an Olympus DP-071 camera.The terminology used for species description followed Round et al. (1990).Taxa identification was based, whenever possible, with the original literature referred to in the text.Samples were deposited in the Herbário of Universidade Estadual de Maringá (HUEM).
To record the occurrence of taxa distribution was conducted a review of literature with taxonomic approach.
Valves slightly heteropolar, lanceolate, with apices rounded and bases attenuate-rounded.Raphe sternum narrow and linear.Raphes lightly sinuous with proximal ends slightly bent towards the stigma.Central area is asymmetrical, expanding until the valve margin is on one side of the valve due to the wider spacing of the median striae.Stigma located close to the medianstria.Striae straight to radiate, with one shortened striaon one side of the central nodule.Areola inconspicuous.Length: 35.8-51.7 µm; width: 7.6-10.5 µm; 9-13 striae in 10 μm.
Gomphonema affine is similar to Gomphonema amoenum Lange-Bertalot in its dimensions and valve outline.
Valves heteropolar, narrow lyclavate-lanceolate, with apices subrostrate and bases attenuate.Raphe sternum linear and narrow.Raphe straight or slightly sinuous, with proxima lends slightly bent towards the stigma.Central area unilateral formed by a shortened median stria.Stigma located close to the median stria.Striae straight, slightly radiate at the ends and with wider spacing at the median region of the valve.Areolae inconspicuous.Length: 16.4-21.1µm; width: 3.5-4.7 µm; 11-15 striae in 10 µm.This species was found in others studies conducted in the state of Paraná.In Tremarin et al. (2009a), this species was found in the macrophyte Potamogeton polygonus and the individuals were larger than observed in our study.
Valves heteropolar, lanceolate, slightly swollen at the median region, with rounded apices and bases.Raphe sternum lanceolate.Raphe sinuous with proxima lends bent towards the stigma.Stigma rounded located close to the central nodule.Striae straight toradiate at the ends, coarse and shortened long the full length of the valve.Areolae conspicuous, difficult to observe.Length: 41.7-48.8µm; width: 7.0-8.2µm; 9-10 striae in 10 µm.
Gomphonema costei and Gomphonema evexus Hohn has very similar valve outline as well as identical dimensions and density of striae, suggesting that the species may be synonymized in the future (Patrick et al., 1966).
Raphe straight with proxima lends bent towards the stigma.Central area unilaterally expanded, delimited by shortened median striae.Stigma located at the end of the median stria.Striaeuniseriate, straight to slightly radiate, with central striae more widely spaced than the others.Areola inconspicuous.Length: 21.1-25.8µm; width: 5.8-6.4µm; 14-16 striae in 10 µm.
Valves clavate, swollen at the median region and with little pronounced constriction between the median region and the apex.Apices widely rounded and bases attenuate-rounded.Raphe sternum narrow and linear.Raphe sinuous with proxima lends dilated in a pore shape, bent towards the stigma.Central area irregular delimited by shortened median striae.Stigma present.Striae uniseriate and radiate, formed by conspicuous areolae.Length: 21.1-25.8µm; width: 5.8-6.4µm; 14-16 striae in 10 µm.Reichardt (2001) reviewed the species Gomphonema truncatum Ehrenbergand G. capitatum Ehrenberg and proposed G. laticollum Reichardt because it presents striae less pronounced constriction close to the valve apices.
In this study, only Gomphonema neonasutum is the first record to the state of Paraná (Table 1).The species that have been widely distributed was G. lagenula and G. parvulum.Only Gomphonema lagenula Kützing, a species with cosmopolitan distribution, occurred in all sampling sites and in all months.
The Ipoitã Channel is influenced hydrologically by Paraná and Ivinhema rivers.The sampling site 3, located close to the Ivinhema River, was the most species-rich area (Table 2).This can be explained by the characteristics of the Ivinhema River, which has natural hydrodynamics, and because it is located in a protected area where there is still marginal vegetation and many flood areas (Souza Filho & Stevaux, 1997).
The lowest number of taxa occurred in the sampling site 1, at the connection with the Paraná River (Table 2).Paraná River is strongly impacted by dams and has higher water transparency and lower nutrient concentrations (Agostinho et al., 2008, Roberto, Santana, & Thomaz, 2009).The differences between these rivers may help to explain the distribution of species in the floodplain, and even the success of some species in certain habitats.Fluctuations in the water level of the Ivinhema River are independent from levels in the Paraná River (Souza Filho, Comunello, & Rocha, 2005), and this pattern also contributes to increase habitat heterogeneity among different riverine habitats in the floodplain (Roberto et al., 2009), elevating the biodiversity in this area.Higher periphyton biomasses, for example, are usually found in the Ivinhema River, which carries more phosphate than the Paraná River (Leandrini, Fonseca, & Rodrigues, 2008).

Conclusion
The present study contributes to the knowledge regarding diatom biodiversity in this region, and it provides support to future ecological and biomonitoring studies in the Upper Paraná River Floodplain.The results emphasize the lack of taxonomic studies for the region and the importance thereof to the knowledge of biodiversity.

Figure 1 .
Figure 1.Upper Paraná River floodplain.The dashed line indicates the Ipoitã Channel.

Table 2 .
Taxa distribution of Gomphonema recorded in Ipoitã Channel in the Upper Paraná River floodplain, located between the states of Mato Grosso do Sul and Paraná.