Diatoms (Bacillariophyceae) of Iguaçu National Park, Foz do Iguaçu, Brazil

Th is study represents a taxonomic survey of class Bacillariophyceae diatoms found in samples collected in the Iguaçu River (Iguaçu National Park, municipality of Foz do Iguaçu, in the state of Paraná, Brazil) between August 2007 and July 2008. Two sampling stations were utilized, the fi rst located upstream of Iguaçu Falls (Cais Bananeiras Station) and second downstream of the falls (Cais Macuco Safari Station). Th e study resulted in the identifi cation of 86 taxa, including 74 at the specifi c level and seven taxonomic varieties. Two of these had never before been documented in the state of Paraná: Gomphonema gibberum Hustedt and Pinnularia meridiana Metzeltin & Krammer. Nine are fi rst-time records for Brazil: Cymbella charrua Metzeltin, Lange-Bertalot & García-Rodríguez, Placoneis ovillus Metzeltin, Lange-Bertalot & García-Rodríguez, Gomphonema affi nopsis Metzeltin, Lange-Bertalot & García-Rodríguez, , Gomphosphenia lingulatiformis (Lange-Bertalot & Reichardt) Lange-Bertalot, Luticola aequatorialis (Heiden) Lange-Bertalot & Ohtsuka, Sellaphora garciarodriguezii Metzeltin & Lange-Bertalot, Eolimna submuralis (Hustedt) Lange-Bertalot Kulikovskiy, Geissleria neosubtropica Metzeltin, Lange-Bertalot & García-Rodríguez and Stauroneis cf. sylviabonillae Metzeltin, Lange-Bertalot & García-Rodríguez.


Introduction
Th e class Bacillariophyceae is comprised of pennate diatoms having a raphe in one or both valves (Round et al. 1990).Th is constitutes the largest group of diatoms (ca.98 genera) and is constantly expanding due to the proposal of new genera (Lange-Bertalot 1995;Round & Bukhtiyarova 1996;Krammer 1999).Members of this class are predominant in lotic environments due to their various forms of fi xation and adaptations to high-turbulence environments (Round et al. 1990).
In Brazil, fl oristic and ecological studies on diatoms are concentrated mainly in the south and southeast.However, works on lotic Bacillariophyceae are scarce (Brassac & Ludwig 2006, Fontana & Bicudo 2009).In the state of Paraná, Soares et al. (2011) conducted studies of lotic systems in the Ribeirão Camberley basin and identifi ed nine taxa within the family Amphipleuraceae; and Ferrari & Ludwig (2007) inventoried 32 taxa from the classes Coscinodiscophyceae, Fragilariophyceae and Bacillariophyceae (Ach-nanthales) in the Ivaí River basin.In the coastal basin, Landucci & Ludwig (2005) recorded 20 species from the classes Coscinodiscophyceae and Fragilariophyceae.Tremarin et al. (2008aTremarin et al. ( , 2008b) ) found 40 taxa under Eunotia Ehrenberg and 28 from the order Th alassiosirales.In a study on the Pinnulariaceae of the Guaraguaçu River, also in the coastal basin, Tremarin et al. (2010) recorded 51 taxa.
Th e Iguaçu River basin is the lotic system with the best known diatom fl ora in the state of Paraná.Th e fl oristic surveys began with Moreira-Filho et al. (1973), who conducted sampling in the water catchment region of Curitiba.Subsequently, Ludwig & Flôres (1995, 1997) conducted surveys in rivers in the areas near the Segredo hydroelectric plant, and Brassac et al. (1999) identifi ed centric diatoms in rivers in the region surrounding the Salto Caxias hydroelectric plant.Later, Brassac & Ludwig (2003, 2005, 2006) conducted a survey of the pennate diatoms of the Iguaçu River and of some tributaries in the Salto Caxias hydroelectric plant region.In the most recent taxonomic study of the Iguaçu River basin (in the Maurício River), Tremarin et al. (2009a) identifi ed 19 taxa of Gomphonema Ehrenberg and one of Gomphosphenia Lange-Bertalot.
Th e present work aims to continue the survey of the taxonomic composition of the class Bacillariophyceae diatoms of the Iguaçu River, in the area encompassed by Iguaçu National Park, in order to broaden knowledge about the taxonomic diversity of these organisms in the area of study.

Material and methods
Th e Iguaçu National Park comprises approximately 169,765 ha and includes 14 of the municipalities of Paraná.Th e park represents the largest conservation area in the Atlantic Forest biome, and is considered one of the last remnants of this vegetation type in the southern region of the country.Th e climate is temperate (a mild, extremely humid, mesothermal climate with no dry season), with an average annual temperature between 18°C and 20°C.Th e maximum temperature ranges from 34°C to 36°C, and the minimum temperature ranges from 4°C to 8°C.Th e average annual rainfall varies between 1,500 and 1,750 mm (IBAMA 1999).
Th e Iguaçu River basin (25°05'S to 26°45'S; 48°57'W to 54°50'W) is located in the southern portion of the state of Paraná, crossing over into the state of Santa Catarina, as well as into some parts of Argentina (Silva et al. 2001;SUDERHSA 1997;Maack 1981).It has 70,800 km 2 of drainage area and stretches 1,275 km from east to west.In the portion preceding Iguaçu Falls, the river is 1,200 m across, narrowing to 65-100 m wide downstream (IAP 2011).
We selected two sampling stations, both located in the municipality of Foz do Iguaçu, on the Iguaçu River.Th e fi rst, situated upstream of Iguaçu Falls (Fig. 1) and called Cais Bananeiras, has an average water speed of 0.42 m s −1 and a depth that varies from 0.90 m when conditions are relatively dry to 4.62 m in the months of higher water volume.Th e second station, located downstream of the Falls and called Cais Macuco Safari, has an average water speed of 6.80 m s −1 and a depth that varies from 4.62 to 27.0 m.
Phytoplankton samples were collected monthly between August 2007 and July 2008 at the two sampling stations, for a total of 24 samples (Tab.1).Samples were collected in 500 ml of river water, obtained by immersing a beaker below the surface of the water.Th e samples were preserved with Transeau solution (Bicudo & Menezes 2006) and oxidized according to technique devised by Simonsen (1974), modifi ed by Moreira-Filho & Valente-Moreira (1981), and deposited in the Universidade Estadual do Oeste do Paraná (UNOP, Western Paraná State University) Herbarium.
To analyze the material under light microscopy, permanent slides were made using Naphrax ® mountant (refractive index, 1.74; Brunel Microscopes Ltd., Chippenham, UK).Photomicrographs were obtained through the use of an Olympus BX60 microscope coupled to an Olympus DP71 digital camera (Olympus, Tokyo, Japan).For all taxa, valves measures were provided (L: length W: width, S: striae; DS: dorsal striae; VS: ventral striae, MS: median striae; AS: apical striae; AC: alar canals; F: fi bulae; A: areolae).For new records for the state of Paraná, or for Brazil, and for those specimens that were particularly diffi cult to identify, descriptions and relevant comments were added.Th e terminology employed was that used by Round et al. (1990) and Barber & Haworth (1981).Th e identifi cation of taxa was based on classic and recent works, including Krammer (2002), Metzeltin & Lange-Bertalot (1998, 2007), Metzeltin et al. (2005), Reichardt (2005) and Siver et al. (2005).

Results and discussion
In this study, we found 86 diatom taxa in 16 families and 28 genera, with fi ve at the generic level, 74 at the specifi c level and seven taxonomic varieties.Th ose taxa whose occurrence had already been documented for the state of Paraná are listed in Tab. 2, along with the morphometric and frequency data.Th e newly documented taxa for the state and for Brazil, as well as those taxa that were particularly diffi cult to identify, are described below, by family.Metzeltin, Lange-Bertalot & García--Rodríguez, Iconogr. Diatomol. 15: 39, pl. 120, fi g. 1-4;121: 1-2, 2005. Fig. 10-11 Dorsiventral valves, dorsal margin distinctly convex, ventral margin gently swollen medially; ends truncated; raphe sternum linear and narrow, central area elliptical with a ventral stigma; raphe arched, distal ends dorsally defl ected and proximal ends straight to slightly dorsally defl ected; radiate striae in the median region and along the ventral valve edge, converging near the dorsal edge; conspicuous areolae.L: 61.4-75 μm; W: 19.3-24 μm; DS: 8-10 μm; VS: 10 in 10 μm; A: 15-16 in 10 μm.
Placoneis serena was previously cited for the state of Paraná, in the São João River in the Ivaí River basin, by Ferrari (2004) and documented by Tremarin et al. (2009b).Specimens observed in that study showed 2-3 and 1-2 shortened striae, respectively, in the median valve region, as did those illustrated by Ferrari (2004).However, the specimens described by Frenguelli (1941) and Metzeltin et al. (2005) showed no shortened striae in the median valve region.Th erefore, further studies are needed in order to determine whether this diff erence implies the proposal of a new taxon or can be considered variability of the species.
Gomphonema affi nopsis diff ers from G. mexicanum in the shape of the stigma, which is transapically elongated in the former and punctiform in the latter, as well as in that it has a lower density of areolae in the striae (15-18 in 10 μm) (Metzeltin et al. 2005) Valves lanceolate with apices cuneate to attenuated--rounded and bases attenuated-rounded; central area indistinct; raphe sternum broad and lanceolate, bounded by regular shortening of the striae; absence of stigma; raphe straight with proximal ends dilated into small pores; striae parallel to slightly radiate at the ends, shortened regularly throughout the length of the valve; areolae inconspicuous.L: 28.4-63 μm; W: 6.7-10.5 μm; S: 9-11 in 10 μm.
Occurrence: fi rst citation for the state of Paraná.
Gomphonema sp.resembles G. pumilum (Grunow) Reichardt & Lange-Bertalot with regard to the valve shape and measures, although the latter has longer and more densely arranged striae (11-12 in 10 μm) than Gomphonema sp.(Krammer & Lange-Bertalot 1991).Further studies are needed in order to determine whether the taxon constitutes a new species.
Occurrence: fi rst citation for Brazil.
Th is taxon is similar to Sellaphora sp.1 with regard to the elliptic-lanceolate valve shape and the delicate striae.However, Sellaphora sp.1 presents more strongly convex margins, larger valves (45 μm) and lower striae density (16 in 10 μm).
Th e specimens found showed similarity to Sellaphora sp.1 and Sellaphora sp.2 regarding the presence of delicate, hard-to-see striae, but are diff erentiated mainly by the capitate shape of the valve ends.
Eolimna submuralis resembles Navicula seminuloides Hustedt and N. muralis Grunow mainly in the elliptical shape of the valves.However, N. seminuloides has a higher striae density (20-24 in 10 μm).While N. muralis presents a smaller central area and striae radiate to parallel at the ends and in higher densities (30 in 10 μm) (Hustedt 1966).
Occurrence: fi rst citation for Brazil.
Th e specimens encountered were similar to Navicula paanaensis A. Cleve-Euler with regard to valve shape and size.However, the two species diff er in valve width and striae density, as well as in the shape and size of the central area.According to Hustedt (1961-66), N. paanaensis presents a width of 6.0-7.5 μm, approximately 20 striae in 10 μm and its central area is smaller than Eolimna sp., formed by alternating long and short striae on either side of the valve.
Occurrence: fi rst citation for Brazil.

Figure 1 .
Figure 1.Location of the Cais Macuco Safari and Cais Bananeiras collection stations, Iguaçu National Park, in the state of Paraná, Brazil.Source: Iguaçu National Park Geoprocessing Department 2011.

Table 1 .
Collection dates, accession numbers and names of collectors of samples deposited at the Western Paraná State University Herbarium.

Table 2 .
Morphometric and frequency data for diatoms at Cais Bananeiras and Cais Macuco Safari collection stations, Iguaçu River, Iguaçu National Park.