Rare Freshwater Research Articles

New ecological notes on the freshwater chrysophycean alga Hydrurus foetidus (Chrysophyceae, Heterokontophyta): a study from Serbia

Hydrurus foetidus (Chrysophyceae, Ochrophyta) is a freshwater benthic alga that appears as a mucilaginous, filamentous thallus. It is geographically widespread but restricted to cold waters, with optimal temperatures for growth between 2°C and 12°C. The lethal temperature for this alga is 16°C. This paper reports the second occurrence of H. foetidus in waters with temperatures much above the recorded lethal temperature. In addition, we describe the non-obligate Hydrurus–Paralemanea association for the first time, with Paralemanea being a substrate for Hydrurus growth. This non-obligate association may be a strategy for the species’ survival during the summer season or the species’ response to climate change. Furthermore, we present co-occurring macroalgae, with special emphasis on the first finding of the rare freshwater chrysophycean alga Phaeodermatium rivulare in Serbian aquatic ecosystems.

Effects of High-Pressure Homogenization on the Structure and Functional Properties of Solenaia oleivora Proteins.

Solenaia oleivora, a rare freshwater shellfish with high protein quality, is unique to China. However, the poor hydrosolubility and functional properties of Solenaia oleivora proteins hinder their utilization in food products. Herein, the alkaline dissolution-isoelectric precipitation method was used for the extraction of Solenaia oleivora proteins. Furthermore, the impact of high-pressure homogenization (HPH) treatment varying from 0 to 100 MPa on the structure and functional properties of Solenaia oleivora proteins was investigated. The obtained results indicated that HPH treatment decreased the α-helix content and enhanced the β-sheet and random coil content. Furthermore, the HPH caused the unfolding of protein structure, exposing aromatic amino acids, increasing the free thiol group content, and enhancing surface hydrophobicity. As the homogenization pressure increased from 0 to 100 MPa, the particle size of Solenaia oleivora proteins decreased from 899 to 197 nm with the polymer dispersity index (PDI) value decreased from 0.418 to 0.151, the ζ-potential increased from -22.82 to -43.26 mV, and the solubility increased from 9.54% to 89.96%. Owing to the significant changes in protein structure and solubility, the emulsifying, foaming, and digestive properties of Solenaia oleivora proteins have been significantly improved after treatment with HPH.

Detour canal, a civil engineering heritage created through historical struggle for water resources, now provides the habitats for a rare freshwater fish.

The Ariake catfish, Tachysurusaurantiacus, is a freshwater fish endemic to Kyushu Island, Japan. However, these catfish are now endangered owing to environmental changes. Despite their status, there is scant quantitative research on the Ariake catfish regarding their potential conservation. The Yabe River is a typical catfish habitat situated in the northern part of Kyushu Island (Ariake Area) and has a unique civil engineering heritage, as represented by the so-called 'detour canal'. The canals were created owing to competition by two Domains to divert additional water resources into their own territory for rice cultivation during the Edo Period (1603-1867). To fill the research gap on the Ariake catfish and assess the ecological value of detour canals, in this study, we conducted a survey of local catfish populations and nine environmental parameters that can affect them. We found that the population volume of the Ariake catfish was significantly higher in canals than in ordinary branch rivers. Although the detour canals were not originally constructed for biodiversity conservation, they nonetheless unintentionally provide catfish habitat at present. As these canals represent a remarkable example of a contribution by a civil engineering heritage structure to biodiversity conservation, our study should be used as a potential justification for preserving the canals, as well as conserving the aquatic species that utilise them as vital habitat.

New Discovery of the Rare Freshwater Brown Alga Pleurocladia lacustris A. Braun (Ectocarpales, Phaeophyceae) in Ukraine (the Khadzhybey Estuary)

A new locality of the freshwater brown alga <i>Pleurocladia lacustris</i> A. Braun, rare for Ukraine, was found. This species is classified as endangered in many European countries and is included in various protection lists. On the whole, about 50 habitats of <i>Pleurocladia lacustris</i> are known in the world, including Europe, North America, Australia, and Africa. For many decades, this is the second record of this alga in Ukraine, which was previously considered extinct here. It was found in the Khadzhybey estuary of the Black Sea in autumn 2023 at a depth of 0.5 m, water temperature 5.3 °C, salinity 4.83 ‰, and pH 8.58. The alga occurred as an epiphyte on <i>Phragmites australis</i> (Cav.) Trin. ex Steud. and <i>Ruppia maritima </i>L. Its thallus was up to 5 mm long, slightly branched on one side, cells somewhat slimy, at the base impregnated with lime. The fouling formed a rather hard cover on the parts of flowering aqautic plants. In the fouling, <i>Pleurocladia lacustris</i> was accompanied by <i>Cladophora glomerata </i>(L.) Kütz. and <i>Ulva flexuosa </i>Wulfen.

The Complete Mitochondrial Genome and Phylogenetic Analysis of the Freshwater Shellfish Novaculina chinensis (Bivalvia: Pharidae).

Razor clams, belonging to the Pharidae and Solenidae families, are ecologically and economically important; however, very little research has been conducted on the Pharidae family. The genus Novaculina is a marine-derived freshwater lineage, and Novaculina chinensis is a rare freshwater species of the Pharidae family. In order to understand the phylogenetic relationships of N. chinensis, we sequenced the mitochondrial genome of the genus Novaculina, which is 16,262 bp in length and consists of 12 protein-coding genes (PCGs), 22 transfer RNA genes (tRNAs), and 2 ribosomal RNA genes (rRNAs). The phylogenetic relationships of 69 Imparidentian mitochondrial genomes (mitogenomes) indicated that N. chineisis is closely related to Sinonovacula constricta of the order Adapedonta. Our study also found that the Ka/Ks ratios of 12 protein-coding genes in the Pharidae family are lower than one, indicating the occurrence of negative purification selection. Morphological observations of the siphons of N. chinensis, Novaculina myanmarensis, and Novaculina gangetica indicate that N. chinensis may be the ancestral clade of the genus Novaculina, which has not been proposed in previous studies. Our study provides useful molecular information on the phylogenetic and evolutionary relationships of Pharidae and also contributes to the conservation and management of the germplasm resources of N. chinensis.

Quantitative PCR (qPCR) assay for the specific detection of the Chinese mystery snail (Cipangopaludina chinensis) in the UK.

Cipangopaludina chinensis Gray 1833 is an East Asian freshwater snail and invasive species in many parts of the world (Global Invasive Species Database, 2022). Within the UK, it was first found at the Pevensey Levels, Sussex, and has since been reported at a second site at Southampton Common, Hampshire. Both sites are designated as Sites of Special Scientific Interest (SSSI) for their wildlife importance. Although the impacts of this species within the UK have not yet been investigated several exotic parasites of the snail have been reported and research suggests that its presence can negatively impact native snail species. This is especially important at the Pevensey Levels due to the presence of the rare freshwater mollusc Anisus vorticulus (Little Whirlpool Rams's-horn snail). Here, we have developed a qPCR-based eDNA assay for the detection of C. chinensis and compared water samples tested for eDNA with results from manual survey of the ditches at the Pevensey Levels. Our eDNA analysis exhibited an overall observed percentage agreement of 80% with a kappa coefficient of agreement between manual and eDNA surveys of 0.59 (95% CI 0.31 to 0.88). Some samples which were qPCR negative for C. chinensis were positive by manual survey, and vice versa revealing the potential for improved overall detection rates when using a combination of manual and eDNA methodologies. eDNA analysis can therefore augment manual survey techniques for C. chinensis as a relatively quick and inexpensive tool for collecting presence and distribution data that could be used to inform further manual surveys and control measures within the ditches.

Predicting climate heating impacts on riverine fish species diversity in a biodiversity hotspot region

Co-occurring biodiversity and global heating crises are systemic threats to life on Earth as we know it, especially in relatively rare freshwater ecosystems, such as in Iran. Future changes in the spatial distribution and richness of 131 riverine fish species were investigated at 1481 sites in Iran under optimistic and pessimistic climate heating scenarios for the 2050s and 2080s. We used maximum entropy modeling to predict species’ potential distributions by hydrologic unit (HU) occupancy under current and future climate conditions through the use of nine environmental predictor variables. The most important variable determining fish occupancy was HU location, followed by elevation, climate variables, and slope. Thirty-seven species were predicted to decrease their potential habitat occupancy in all future scenarios. The southern Caspian HU faces the highest future species reductions followed by the western Zagros and northwestern Iran. These results can be used by managers to plan conservational strategies to ease the dispersal of species, especially those that are at the greatest risk of extinction or invasion and that are in rivers fragmented by dams.

New distributional records and rediscovery of three rare freshwater mussels (Bivalvia, Unionidae) in the Sequatchie River, Tennessee

We present new drainage records for five freshwater mussels in the Sequatchie River, a tributary of the Tennessee River. We also report the rediscovery of Purple Lilliput, Toxolasma lividum Rafinesque, 1831, Tennessee Pigtoe, Pleuronaia barnesiana (Lea, 1838), and the federally endangered Slabside Pearlymussel, Pleuronaia dolabelloides (Lea, 1840), and we provide information on other mussel species found in our survey. In the Sequatchie River, T. lividum was last seen in 1957 and P. barnesiana and P. dolabelloides were last seen in 1980. The discovery of five new drainage records and rediscovery of three rare species highlights the need for additional mussel surveys in the Sequatchie River and the importance of surveys in conservation efforts.

Postglacial environmental change inferred from carbonate‐ and organic‐rich sediments of groundwater‐fed Kelly Lake, Kenai Peninsula, south‐central Alaska

ABSTRACTMajor shifts in hydroclimate have been documented during the last deglacial period and the Holocene in south‐central Alaska. Rare freshwater calcium carbonate (marl) deposits in lakes on the Kenai Peninsula can be used to reconstruct past changes in hydroclimate, including the influence of groundwater inflow to lakes. Here, the postglacial sediment sequence from groundwater‐fed Kelly Lake (60.514°N, 150.374°W) was analyzed for multiple proxies including isotopes of carbon and oxygen in marl calcite (δ13Cmarl and δ18Omarl), and isotopes of carbon (ẟ13COM) and abundances of C and N in organic matter. Bulk sediment analyses include organic matter and calcium carbonate (CaCO3) contents, visual stratigraphy and sediment flux. These analyses extend those of a previous paleoenvironmental reconstruction from Kelly Lake, which focused on sedimentary diatom oxygen isotopes and mass balance modeling over the past 10 000 years. Here, we show that Kelly Lake was deglaciated prior to 14.6 ka, and that by 14.0 ka marl dominated the sediments, with CaCO3 precipitation probably driven by groundwater input and mediated by shallow‐water charophytes. Marl accumulation decreased as organic and clastic inputs increased between ~12.2 and 11.5 ka. This shift, together with an increase in both δ13Cmarl and δ18Omarl values and a decrease in CaCO3 content, indicates an increase in the influence of meteoric water on the hydrologic budget under wet conditions, possibly driven by a strengthened Aleutian Low atmospheric pressure cell. A shift to lower δ13Cmarl and δ18Omarl values at ~11.5 ka is interpreted as an increase in the proportion of groundwater relative to meteoric water in the lake. Beginning around 9 ka, the proportion of meteoric water input continued to increase, the surrounding coniferous forest was established, and by 8 ka, CaCO3 accumulation ended. Our results elucidate the environmental conditions under which marl was deposited during the Lateglacial and early Holocene in this part of Alaska, and demonstrate how a variety of synoptic‐ and local‐scale climatic variables can converge to influence sedimentation in a groundwater‐fed lake.

Evaluation of Threatened, Endangered, and Rare Fish Species and Communities of the St. Lawrence River and Its Tributaries in the United States

Biodiversity is responsible for important ecological processes like productivity and ecosystem stability, and rare species are a major component of biodiversity. Rarity increases a species' vulnerability to disturbances and also makes them difficult to study. Globally, species of freshwater systems are some of the most threatened, and evaluation of rare freshwater species and their habitats is needed to help preserve natural flexibility and ecological function. We conducted an analysis of full fish communities of the upper St. Lawrence River and its major US tributaries, with the goals of determining species locations and abundances, associated environmental conditions, the distribution of distinct fish assemblages across the landscape (with emphasis on communities supporting rare species), and potential threats. From 2009 to 2015, the US Geological Survey (USGS) and Saint Regis Mohawk Tribe (SRMT) worked together using standardized methods to collect community samples within 4 different aquatic realms (shallow and deep lentic, and small and large lotic systems) and determine species-specific fish abundances, frequencies of occurrence, and associated habitat signatures and spatial distributions. Distinct fish assemblages and associated habitat conditions were objectively identified by multivariate and hypothesis-testing methods. We used a geographic information system (GIS) to spatially associate habitat, biotic, and landscape attributes within each stream reach throughout the study area, facilitating quantification of distribution patterns. Comparisons with historical data provided estimates of loss or gain of threatened and endangered species (T&E) colonies. We developed a disturbance index to highlight potential threats to aquatic species. More than 140,000 fishes of 87 species were collected from a total of 1140 sample sites, covering 278 stream reaches, including the endangered Notropis anogenus (Pugnose Shiner), and threatened Hiodon tergisus (Mooneye), Etheostoma pellucidum (Eastern Sand Darter), and Acipenser fulvescens (Lake Sturgeon). We identified 50 distinct fish assemblages differing in species composition, abundance, and/or diversity, but only 13 of those assemblages included a T&E species. The rareness, extent, and patchiness of fish assemblages created a mosaic of fish communities across the landscape, from headwaters to the mainstem of the St. Lawrence River. Comparisons with historic surveys (1978–2008) showed a stable number of T&E species colonies or an increase for some species. The geographic distribution of multimetric disturbance index values showed where combinations of disturbances to fish habitats might affect rare fish species and aquatic communities in the region. The species–habitat associations and fish assemblage distributions can be used for evaluation of species, communities, or habitats that may need protection or restoration.

Hydrochemical and Seasonally Conditioned Changes of Microbial Communities in the Tufa-Forming Freshwater Network Ecosystem.

Freshwater network ecosystems consist of interconnected lotic and lentic environments within the same catchment area. Using Plitvice Lakes as an example, we studied the changes in environmental conditions and microbial communities (bacteria and fungi) that occur with downstream flow. Water samples from tributaries, interlake streams, connections of the cascading lakes, and the Korana River, the main outflow of the system, were characterized using amplicon sequencing of bacterial 16S rRNA and fungal ITS2 genes. Our results show that different environmental conditions and bacterial and fungal communities prevail among the three stream types within the freshwater network ecosystem during multiple sampling seasons. Microbial community differences were also confirmed along the longitudinal gradient between the most distant sampling sites. The higher impact of "mass effect" was evident during spring and winter, while "species sorting" and "environmental selection" was more pronounced during summer. Prokaryotic community assembly was majorly influenced by deterministic processes, while fungal community assembly was highly dominated by stochastic processes, more precisely by the undominated fraction, which is not dominated by any process. Despite the differences between stream types, the microbial community of Plitvice Lakes is shown to be very stable by the core microbiome that makes up the majority of stream communities. Our results suggest microbial community succession along the river-lake continuum of microbial communities in small freshwater network ecosystems with developed tufa barriers. IMPORTANCE Plitvice Lakes represent a rare freshwater ecosystem consisting of a complex network of lakes and waterfalls connecting them, as well as rivers and streams supplying water to the lake basin. The unique geomorphological, hydrological, biogeochemical, and biological phenomenon of Plitvice Lakes lies in the biodynamic process of forming tufa barriers. In addition to microbial communities, abiotic water factors also have a major influence on the formation of tufa. Therefore, it is important to understand how changes in environmental conditions and microbial community assembly affect the functioning of the ecosystem of a freshwater network with developed tufa barriers.

Water quality assessment of Şehriban stream (Kastamonu, Türkİye) from a multi-statistical perspective

ABSTRACT In this paper, water quality of Sehriban Stream, a rare freshwater ecosystem far from human impact and located in the western part of Türkiye’s Karadeniz Region, was studied over a long period of time (a hydrological year). Multivariate statistical approaches such as Pearson Correlation Index (PCI), Factor Analysis (FA), Cluster Analysis (CA) and self-organising maps (SOM) were used to evaluate the water quality and physico-chemical datasets. Samples were taken monthly during February 2019 – January 2020 from 12 stations and a total of 21 physicochemical parameters were investigated. The spatiotemporal averages of some organic pollution parameters investigated in the basin were determined as follows: 344 μS/cm for EC, 0.80 mg/L for COD, 0.42 mg/L for BOD, 0.02 mg/L for PO4 2-, 34.4 mg/L for SO4 2-, 0.00009 mg/L for NO2, 1.36 mg/L for NO3 and 0.0002 mg/L for NH4 −. According to the findings of this study, despite a modest decline in water quality from upstream to downstream, Sehriban Stream was revealed to have first-class water quality features in general and all parameters detected in all seasons at all the investigated stations were below the limit values reported by WHO. The SOM analysis detected three spatial patterns, e.g. pH-salinity-K+-PO4 2--Mg2+-NO2; DO-Ca2+-NH4 − and TDS-EC-Cl−-SO4 2--COD-BOD-Na+ in water. As a result of PCI, significant positive and negative correlations were recorded among the investigated parameters. Results of FA showed that 2 factors elucidated 85% of total variances, which are named ‘Agricultural Factor’ and ‘Natural Factor’. As a result of CA, 3 significant clusters were identified, which are named ‘Lower Polluted Zone’, ‘Moderate Polluted Zone’ and ‘Higher Polluted Zone’. Overall, this work showed that multi-statistical approaches can be used to assess the water quality in a rare, unpolluted habitat over time and space.

Sub-fossil diatoms from the Saloum Estuary, Senegal, West Africa: Floristic inventory and paleo-productivity evolution along the Ndangonkha core

As part of our program to reconstruct the estuaries and lagoons history in Senegal and the diatom microflora inventory in Sene-Gambia, a 400 cm long core was taken at Ndangonkha in the Saloum Estuary, near Foundiougne. The dating obtained showed that sedimentation began during the Nouakchottian age, around 6000 years BP, with an average rate of sedimentation higher at the base than at the top where the high hydrodynamics of the environment would have caused sediment reworking. The comparative analysis of the lithology and the microflora showed a perfect correlation between the lutite fraction, the absolute abundance of diatoms and their specific richness. The study involved an inventory of 110 species and varieties belonging to 62 genera. The most represented genera being Nitzschia (10 species) and Cyclotella and Diploneis (5 species each). Five species are cited for the first time in Sene-Gambia and 61 species are also reported from Ndangane Babou. The microflora is dominated by euryhaline forms headed by Cyclotella striata. This dominance could be linked to the frequent variations in salinity between the rainy and dry seasons, while the abundance of marine species could be related to the dominant influence of marine waters. The rare freshwater species encountered could be brought by wind, insects or birds. The analysis of the microfloristic and lithological data showed that the primary paleo-productivity and the specific richness are weak at the base but showed an increase upwards. They are high in zone A, maximum in zone C whereas in zone D they are decreasing before disappearing in the last 10 cm, in relation to the hydrodynamics of the environment.

Macroinvertebrate Community Composition in Wetlands of the Desert Southwest is Driven by wastewater-associated Nutrient Loading Despite Differences in Salinity.

The online version contains supplementary material available at 10.1007/s13157-022-01647-2.

A redescription of the rare eucyclopine copepod Eucyclops productus Kiefer, 1939 (Multicrustacea: Copepoda: Cyclopoida: Cyclopidae) and a ke to Eucyclops subgenera and species of China and adjacent areas.

The rare freshwater copepod Eucyclops (Speratocyclops) productus Kiefer, 1939 from Lake Mandongco, Tibet Autonomous Region, China, is redescribed. This species was originally found and described from a pond south of Chushul village, and many of the details did not meet modern standards for describing the species. In this paper, the morphological characteristics of this species are described in detail and compared with other members of the subgenus Speratocyclops species recorded in China. The key features of the species are: 1) long caudal rami, 2) the coxal seta of the fourth pair of legs armed with long hairs in the proximal part and short denticles in the distal part, 3) the inner spine of the fifth pair of legs long and strong. An identification key to 22 species of Eucyclops known from China and adjacent areas is also provided.

Sex-relevant genes in the embryo stage of Chinese soft-shelled turtles as revealed by RNA-Seq analysis

Abstract The Chinese soft-shelled turtle (Pelodiscus sinensis) is an economically important and rare freshwater aquaculture species in China. The male turtles have better economic benefits than females due to their faster growth speed. In order to explore the mechanism of sex differentiation and determination of P. sinensis, transcriptome analysis was carried out using embryo samples from the sex determination, sex differentiation and shelling stages, respectively. The gender types of embryos were identified by genotyping and histological analysis. In all, 277,230 and 273,859 genes were identified from embryos of male and female turtles, respectively. Cluster analysis of gene expression patterns exhibited trends for all differentially expressed genes (DEGs), which can be classified into three subclusters. In the sex determination, sex differentiation, and shelling stages 975, 43, and 300 DEGs, respectively, were identified by comparing the male and female groups. KEGG analysis was used to explore the function of the DEGs. Fgf9, foxl2, mex3b, sox7,tgfβ-3, wnt4, wnt7a, and wt1 were upregulated in ovary development stages and chfr, ampk, aldh2, dao, glt1d1, hvcn1, psmd9, srsf9 and ubc were upregulated in testis development stages, indicating that these genes play important roles in the sex development of P. sinensis. The results of this study provide preliminary insights into the sex determination and differentiation of Chinese soft-shelled turtles.

Genetic assessment of the rare freshwater shrimp

The lack of information is one of the major impediments to effective conservation of rare, endemic species. One of which concerns the freshwater atyid shrimp Caridina logemanni known only from three streams in Hong Kong, with an area of occupancy of less than 20 km2, further threatened by harvesting for aquarium trade and potential introgressive hybridisation with a ubiquitous congener C. cantonensis. Here, we delineated the genetic diversity and population structure of C. logemanni, and examined its extent of hybridisation with C. cantonensis, using one mitochondrial (COI), one nuclear (NaK intron) and six microsatellite markers. The two examined populations of C. logemanni exhibited strong genetic differentiation at a spatial scale of <1.5 km apart, and generally low genetic diversity. Historic introgressive hybridisation is evident from the sharing of COI haplotypes between species and the more extensive inter-specific microsatellite admixture than inter-population admixture, such that both C. logemanni populations were of hybrid origin. Future conservation efforts on C. logemanni should aim at (1) minimising waterway modifications to prevent potential anthropogenic hybridisation, (2) fortifying conservation legislations to stop its harvesting, and (3) conducting continuous monitoring in case of stochastic events associated with small population size and linear habitat.

<i>Flintiella sanguinaria</i> F. D. Ott (Porphyridiales, Rhodophyta) New to India

A rare freshwater unicellular red alga Flintiella sanguinaria F. D. Ott has been reported for the first time from India. It is a monotypic taxon and a rare alga. The alga was found growing as powdery covering on moist burnt soil of a damp paddy field from Rajhat, Chinsurah, West Bengal and collected in the month of January. It has been reported from very few localities of the world. Probably, this is the first report of the genus and species from the Asian subcontinent.

A new genus and two new, rare freshwater mussel (Bivalvia: Unionidae) species endemic to Borneo are threatened by ongoing habitat destruction

Abstract Most of the Bornean endemic freshwater mussel (Unionida) species known to date have not been recorded by science for the past 50 years or more, owing to a lack of research effort and presumed population losses. This study assessed current patterns and recent changes in the diversity and distribution of freshwater mussels in north‐eastern Borneo. Physical surveys and interviews were conducted at 24 sites, and anecdotal evidence for current or historical presence of mussels was collected for a further 13 sites. Native species, i.e. Schepmania sp. and Khairuloconcha sahanae gen. & sp. nov., were only found in one small stream of the Kinabatangan River basin within the Gomantong Forest Reserve, whereas the non‐native Sinanodonta cf. woodiana was common across the study area. Molecular phylogenetics (five genes) of the native taxa, including comparative material from West Kalimantan and Sarawak, revealed: (i) the presence of a new genus with two new, rare species: Khairuloconcha lunbawangorum sp. nov. in the Limbang River basin and K. sahanae in the Kinabatangan River basin; (ii) that Khairuloconcha and Ctenodesma form the Bornean endemic tribe Ctenodesmini trib. nov.; and (iii) that Schepmania represents another Bornean endemic tribe Schepmaniini trib. nov. Both Khairuloconcha gen. nov. species are known from a single stream each and are apparently restricted to forest stream habitats where they occur at very low densities. Schepmania appears to have a severely contracted range in the Kinabatangan and adjacent basins. We urgently call for full protection of the currently known sites of K. lunbawangorum and K. sahanae, and development of an action plan to save the Bornean freshwater mussel fauna.

Morphological features of the Geminella protogenita (Kützing) West (Chlorophyta, Trebouxiophyceae): a rare freshwater green alga found in southern of Brazil

Morphological features of the Geminella protogenita (Kützing) West (Chlorophyta, Trebouxiophyceae): a rare freshwater green alga found in southern of Brazil