We suggest future studies in this environment, once it has propitious characteristics to the development of epilithic diatoms. Moreover, phylogenetic studies are also recommended for a better distinction of taxa with a wide morphologic variation.

The genus Humidophila is mainly characterized by small cells, striae often composed by one elongated areola occluded by thin hymenes. Species are distributed globally and are common in moist sub-aerial habitats. We identified five Humidophila species found in the well-conserved freshwater bodies and subaerial wet habitats from the mountain region "Mananciais da Serra". Four previously known species (Humidophila brekkaensis, H. contenta, H. nienta, H. paracontenta) and one new species (Humidophila piraquarae sp. nov.) were described and illustrated based on light and scanning electron microscopy observations. Humidophila piraquarae sp. nov. is similar to H. nienta (Carter) Lowe, Kociolek, Johansen, Van de Vijver, Lange-Bertalot et Kopalová and H. undulata Lowe, Kociolek, Johansen, Van de Vijver, Lange-Bertalot et Kopalová, but is best distinguished by their prominent constriction, apices broadly rostrate-rounded, striae density, raised siliceous thickening in the apical region of the axial area, and raphe proximal endings laterally expanded in anchorshaped depressions. Addtionally, a list of Humidophila taxa already registered in Brazil is presented.

The Paranaguá Estuarine Complex (PEC) is one of Brazil's largest southwest Atlantic estuarine systems, possessing a rich microalgae diversity that remains to be fully explored. Therefore, due to the increasing interest in the microalgae biotechnological potential, this study isolated and identified diatoms found in the PEC. The diatoms were purified and analyzed with light and scanning electron microscopy for morphological identification, while DNA sequences were used for molecular identification. Although a diatoms rich diversity was obtained, only a few were viable after the cultivation period. The two best-selected strains were identified as belonging to two genera, Nitzschia and Navicula. The rbcL region was found to be the most informative for species identification. Morphological and molecular analyses allowed for the identification of HIGHLIGHTS • Species identification by morphological and molecular analyses • The first rbcL sequence report for Navicula pseudoantonii • First record of Navicula pseudoantonii in the American continent

Temporal stability in beta diversity does not guarantee surrogacy or compositional stability in a micro-phytoplankton meta¬community. In this study, we evaluated phytoplankton community organization (i.e., microalgae filtered in 20 μm mesh-sized plankton net) in a highly dynamic subtropical tidal river over three years. Specifically, we assessed temporal stability in the spatial organization of phytoplankton, the diatoms’ efficiency as an indicator (surrogate group) of ecological patterns of other phytoplankton groups, the temporal variation in species composition, and the beta diversity of a metacommunity. We performed six sampling occasions at the end of the summers and winters from 2017 to 2019 at 16 sampling points comprising a strong en¬vironmental gradient in the Guaraguaçu River, South Brazil. We tested for correlations of community structures from different periods and for correlations between diatoms species and those from other phytoplankton groups using Mantel tests. Species compositions were compared among periods using a permutational multivariate analysis of variance, and temporal variation in metacommunity beta diversity was evaluated using null models. There was temporal stability in the spatial dissimilarities of communities. Diatoms were poorly correlated with the other phytoplankton groups. The temporal stability in spatial structure, a facet of beta diversity, was in line with the temporal stability in compositional variation – a measurement of metacommuni¬ty beta diversity. Our results also showed that such stability was not static, since community compositions varied over time, mainly between seasons. We conclude that even in a highly dynamic tidal river, the temporal stability of spatial organization may indicate that the spatial gradient is so strong that it maintains spatial structuring over time. Such patterns were maintained even with the dynamic species changes over seasons. The fact that different phytoplankton groups do not respond similarly to the spatial gradient reinforces that microalgae should be analyzed separately in ecological studies, and long-term monitoring should consider different algal groups for a complete assessment of ecological patterns.

The biotechnological potential of microalgae has been the target of a range of research aimed at using its potential to produce macromolecules with high added value. Particular focus has been given to biofuels' production, such as biohydrogen, biodiesel, and bioethanol from lipids and carbohydrates extracted from microalgal biomass. Bioprospecting and accurate identification of microalgae from the environment are important in the search for strains with better performance. Methodologies that combine morphology and molecular techniques allow more precise knowledge of species. Thereby, this work aimed to identify the new strain LGMM0013 collected at Iraí Reservoir, located in Paraná state, Brazil, and to evaluate the production of biomass, carbohydrates, and lipids from this new microalgal strain. Based on morphology and phylogenetic tree from internal transcribed spacer (ITS), strain LGMM0013 was identified as Desmodesmus abundans. D. abundans accumulated 1500 mg L-1 of dried biomass after 22 days of cultivation in autotrophic conditions, 50% higher than Tetradesmus obliquus (LGMM0001) (Scenedesmaceae-Chlorophyceae), usually grown in photobioreactors located at NPDEAS at the Federal University of Paraná (UFPR) to produce biomass. Analysis of the D. abundans biomass from showed an accumulation of 673.39 mg L-1 of carbohydrates, 130% higher than T. obliquus (LGMM0001). Lipid production was 259.7 mg L-1, equivalent to that of T. obliquus. Nitrogen deprivation increased the production of biomass and carbohydrates in D. abundans LGMM0013, indicating this new strain greater biomass production capacity.