Soft-bodied benthic algae in pristine Brazilian streams: from acid to karst

Acta Botanica Brasilica - 33(3): 517-529. July-September 2019. doi: 10.1590/0102-33062019abb0086 Soft-bodied benthic algae in pristine Brazilian streams: from acid to karst1 Bárbara Medeiros Fonseca2* , Lidia Mendes Feijó2 and Luciana de Mendonça-Galvão2 Received: March 18, 2019 Accepted: June 17, 2019 . ABSTRACT This study evaluated soft-bodied benthic algae from seven streams located in protected areas of central Brazil (Parque Nacional de Brasília, Parque Nacional da Chapada dos Veadeiros and Parque Estadual de Terra Ronca), and related them to abiotic factors. We addressed the following questions: A) how algal community structure in Cerrado streams is influenced by the marked seasonality typical of the region; and B) how karst geology influences algal communities in Parque Estadual de Terra Ronca, as compared to streams in other Cerrado areas. Samples were collected between 2012 and 2013 from a single site in each stream, and upstream and downstream of caves present in Parque Estadual de Terra Ronca. Altogether, 159 taxa were recorded. Algal community structure varied significantly among sites, but not between seasons, despite relatively lower abundances during the rainy season, likely due to a negative influence of the faster currents in streams during this period. Some alkaliphilic species were observed only at sites near caves (e.g. the cyanobacterium Tolypothrix distorta), while acidophilic taxa were more frequent in the other streams (e.g. desmids and Cyanobacteria such as Scytonema caldarium, Hapalosiphon stuhlmannii and Stigonema ocellatum). We observed a rare green alga, Microthamnion kuetzingianum, and reported the cyanobacterium Rivularia aquatica for the first time in Brazil. Keywords: abiotic variables, biodiversity, Cerrado, Cyanobacteria, lotic systems, periphyton, soft-bodied algae, pristine streams, Zygnematophyceae Introduction All over the world, anthropogenic influence on natural environments is increasing, and pristine aquatic systems are becoming scarce (Lindstrøm et al. 2004). Running waters unaffected by human impact are frequently restricted to areas protected by law (Fonseca et al. 2014; Fonseca & Mendonça-Galvão 2014), and are thus very precious, as they can provide basic knowledge on biological reference conditions (Schneider 2015). Soft-bodied benthic (SB) algae have been defined as non-diatom algae, including cyanobacteria, attached to substrata in lotic environments (Rott & Schneider 2014). Studies on SB algae in reference conditions have been mainly carried out in streams from temperate regions of North America (Thomas et al. 2015; Stancheva & Sheath 2016) and northern Europe (Lindstrøm et al. 2004). In Brazil, this terminology has not been widely used; instead, the literature about benthic or periphytic algae in lotic systems mostly refers to diatoms (e.g. Salomoni et al. 2011; França et al. 2017) or macroalgal communities (e.g. Branco et al. 2001; 2008a; b; Necchi Jr. et al. 2008; Tonetto et al. 2015; 2018), and the majority of them are concentrated in the southeastern/southern regions. Microscopic attached algae from other taxonomical groups are less known, which may lead to underestimated numbers for general phycological diversity in such environments. 1 In memory of Sirlene Aparecida Felisberto 2 Laboratório de Biodiversidade Aquática, Universidade Católica de Brasília, 71966-700, Taguatinga, DF, Brazil * Corresponding author: Bárbara Medeiros Fonseca, Lídia Mendes Feijó and Luciana de Mendonça-Galvão Soft-bodied benthic algae have already provided information for the development of ecological indexes used for monitoring ecological changes or spatial patterns (Schneider & Lindstrøm 2009; 2011; Stancheva et al. 2013; Fetscher et al. 2014; Stancheva & Sheath 2016). Although diatoms have been more studied under this approach and have often been considered the best indicator to reflect environmental conditions when compared to non-diatoms (Kelly et al. 2008), in some temperate countries the study of SB algae alongside diatoms is also mandatory for ecological quality analysis (Poikane et al. 2016). Besides trophic status, other variables such as rainfall, current velocity and turbidity can be important environmental factors that influence periphytic and macroalgal communities in lotic environments, especially in nutrient-poor waters (Branco & Necchi Jr. 1997; Branco et al. 2008b). Sometimes, despite regional variations, particular features of a stream can influence species richness on a local scale, promoting low inter-stream similarities and consequently increasing beta diversity (Rott & Wehr 2016). Such spatial differences have been observed in several studies carried out in the southeastern/southern regions of Brazil (e.g. Branco et al. 2008b; 2009; Tonetto et al. 2015). In central Brazil, a region covered by the Cerrado Domain (Brazilian savanna), seasonality is typically marked by the alternation between dry and rainy seasons (Silva et al. 2008), with consequences for both terrestrial and aquatic ecosystems (Fonseca & Mendonça-Galvão 2014). Cerrado pristine waters generally have a slightly acidic pH, with low electrical conductivity and low nutrient concentrations (Markewitz et al. 2006; Fonseca et al. 2014). However, some limestone outcrops with karst geology are also found in the region, generally belonging to the Brazilian sedimentary unit known as the Bambuí Group (Faquim et al. 2017), promoting alkaline waters and higher electrical conductivity (Righi-Cavallaro et al. 2010). Variation in these chemical variables (pH and electrical conductivity) can result in marked differences in algal community structure (Mutinová et al. 2016). The Parque Estadual de Terra Ronca(hereafter PETeR), one of the three protected areas considered in the present study, comprises the biggest South American cave complex, and its karst geology contrasts with the other two areas, Parque Nacional de Brasília(hereafter PNB) and Parque Nacional da Chapada dos Veadeiros(hereafter PNCV). These three protected areas are located in the core of the Cerrado Domain, at a distance of 160 km to 250 km from one another. Ecological studies on benthic or periphytic algae in lotic systems in central Brazil, especially unpolluted ones, are very scarce (e.g. França et al. 2017), despite their importance as primary producers and their strategic position at the bottom of trophic cascades (Necchi Jr. 2016). For this study, our aim was to address two main questions: A) how algal community structure in Cerrado streams is influenced by the marked seasonality typical of the region; and B) how karst geology influences the algal communities in Parque Estadual de Terra Ronca, as compared to streams in other Cerrado areas. Special attention was also given to identifying rare taxa, or those that are characteristic of particular habitats. Materials and methods Study area This study was carried out in seven pristine streams located in three protected areas in the Cerra (...truncated)