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The structure of phytoplankton during the under-ice period in northern oligotrophic lakes (Lake Krivoe and Lake Krugloe) has been considered and its level of development during ice melt is assessed. In winter 2019–2021, cyanobacteria, diatoms, and cryptophyte algae were noted in phytoplankton. The phytoplankton spring increase in Lake Krivoe was due to the development of the dinophyte Peridinium aciculiferum and, in Lake Krugloe, to the diatom Aulacoseira subarctica. Biomass varied from 0.003 to 0.083 mg/L in winter and up to 0.65 mg/L in spring. The spring peak (April–May) of phytoplankton is associated with the development of dinophyte algae and exceeded summer values. The average Chl a concentration in plankton reached 0.3–0.4 μg/L. The cryoflora contained algae frozen into the ice in an inactive state (0.003–0.04 mg/L). The development of phytoplankton under the ice makes an important contribution to the productivity of northern lakes. [ABSTRACT FROM AUTHOR]

Seasonally slowly melting mountain snowfields are populated by extremophilic microalgae. In alpine habitats, high‐light sensitive, green phytoflagellates are usually observed in subsurface layers deeper in the snowpack under dim conditions, while robust orange to reddish cyst stages can be seen exposed on the surface. In this study, uncommon surface green snow was investigated in the High Tatra Mountains (Slovakia). The monospecific community found in the green surface bloom consisted of vegetative Chloromonas cells (Volvocales, Chlorophyta). Molecular data demonstrated that the field sample and the strain isolated and established from the bloom were conspecific, and they represent a new species, Chloromonas kaweckae sp. nov., which is described based on the morphology of the vegetative cells and asexual reproduction and on molecular analyses of the strain. Cells of C. kaweckae accumulated approximately 50% polyunsaturated fatty acids, which is advantageous at low temperatures. In addition, this new species performed active photosynthesis at temperatures close to the freezing point showed a light compensation point of 126 ± 22 μmol photons · m−2 · s−1 and some signs of photoinhibition at irradiances greater than 600 μmol photons · m−2 · s−1. These data indicate that the photosynthetic apparatus of C. kaweckae could be regarded as adapted to relatively high light intensities, otherwise unusual for most flagellate stages of snow algae. [ABSTRACT FROM AUTHOR]

Red snow caused by spherical cysts can be found worldwide, while an orange snow phenomenon caused by spherical cells is restricted to (Sub-)Arctic climates. Both bloom types, occurring in the same localities at Svalbard, were compared ecophysiologically. Using a combination of molecular markers and light- and transmission electron microscopy, cells were identified as Sanguina nivaloides and Sanguina aurantia (Chlorophyceae). In search for reasons for a cosmopolitan vs. a more restricted distribution of these microbes, significant differences in fatty acid and pigment profiles of field samples were found. S. aurantia accumulated much lower levels of polyunsaturated fatty acids (21% vs. 48% of total fatty acids) and exhibited lower astaxanthin-to-chlorophyll-a ratio (2–8 vs. 12–18). These compounds play an important role in adaptation to extreme conditions at the snow surface and within snow drifts. Accordingly, the performance of photosystem II showed that one third to nearly half of the photosynthetic active irradiation was sufficient in S. aurantia, compared to S. nivaloides, to become light saturated. Furthermore, formation of plastoglobules observed in S. nivaloides but missing in S. aurantia may contribute to photoprotection. The rapid light curves of the two species show to a certain extent the shade-adapted photosynthesis under the light conditions at Svalbard (high α-value 0.16 vs. 0.11, low saturation point Ik 59 vs. 86). These results indicate significant physiological and ultrastructural differences of the two genetically closely related cryoflora species, but the reasons why S. aurantia has not been found at conditions outside (Sub-)Arctic climate types remain unknown. [ABSTRACT FROM AUTHOR]

Abundance and biomass of small photosynthetic flagellates (SPF; 3–10 µm), chlorophyll a concentration, and the contribution of SPF to total phytoplankton biomass at different stages of seasonal succession in ice and in surface water were studied in Kandalaksha Bay of the White Sea in September 2016 and February and July 2017. In summer, SPF biomass in the photic layer averaged 38.36 ± 9.77 mg C/m3, 2.22 ± 1.43 mg C/m3 in autumn, 2.6 ± 1.72 mg C/m3 in under-ice water, and 14.79 ± 11.25 mg C/m3 in ice. The contribution of SPF to total phytoplankton biomass depended on the season and ranged from 29 to 95%; the contribution of SPF to sympagic communities averaged 66%. The size structure of photosynthetic flagellates varied by seasons. Flagellates with a cell size of 6–10 µm dominated in summer plankton and in the ice. Flagellates with a cell size of 3–6 µm prevailed in autumn and in the under-ice water. The obtained data of SPF abundance showed higher values of the total phytoplankton biomass of the White Sea in the autumn–winter period compared with the estimates obtained previously. Applying the method of epifluorescence microscopy confirmed the idea that photosynthetic flagellates were the main producers in the winter period as well as in the summer when the biomass of planktonic algae with cell size exceeding 10 µm is low. [ABSTRACT FROM AUTHOR]

Melting polar and alpine ice surfaces frequently exhibit blooms of dark pigmented algae. These microbial extremophiles significantly reduce the surface albedo of glaciers, thus accelerating melt rates. However, the ecology, physiology and taxonomy of cryoflora are not yet fully understood. Here, a Swiss and an Austrian glacier dominated either by filamentous Ancylonema nordenskioeldii or unicellular Mesotaenium berggrenii var. alaskanum, were sampled. Molecular analysis showed that both species are closely related, sharing identical chloroplast morphologies (parietal-lobed for Ancylonema vs. axial plate-like for Mesotaenium sensu stricto), thus the unicellular species was renamed Ancylonema alaskana. Moreover, an ecophysiological comparison of the two species was performed: pulse–amplitude modulated (PAM) fluorometry confirmed that they have a high tolerance to elevated solar irradiation, the physiological light preferences reflected the conditions in the original habitat; nonetheless, A. nordenskioeldii was adapted to higher irradiances while the photosystems of A. alaskana were able to use efficiently low irradiances. Additionally, the main vacuolar polyphenol, which effectively shields the photosystems, was identical in both species. Also, about half of the cellular fatty acids were polyunsaturated, and the lipidome profiles dominated by triacylglycerols were very similar. The results indicate that A. alaskana is physiologically very similar and closely related but genetically distinct to A. nordenskioeldii.

Long-lasting, slowly melting snowfields in mountainous regions are frequently populated by specialised microalgae whose diversity is still vastly underestimated. Cysts causing sub-surficial green snow were collected in the Austrian Alps, Tyrol, and morphologically accorded to the snow alga Scotiella cryophila sensu Chodat, initially described from Switzerland. The cytology and photobiology of this population were investigated to understand mechanisms of adaptation to the harsh habitat. Cysts of S. cryophila K-1 had secondary cell walls with pronounced rib-like surface structures and contained several small spherical plastids. The cytoplasm was dominated by lipid bodies, which developed reddish secondary pigmentation. Partial life cycle observations showed that daughter cells lacked structured cell walls. Cysts performed active photosynthesis at temperature conditions close to the freezing point and were photoinhibited at irradiances greater than 70 μmol m−2 s−1. This corresponded exactly to habitat conditions 20 to 40 cm below the snow surface. Phylogenetic analyses using 18S rDNA, rbcL and ITS2 rDNA sequences indicated that S. cryophila K-1 is related to Chloromonas, known to contain several snow algae. The taxon forms an independent lineage and is clearly genetically distinct from the type strain of Chloromonas rosae var. psychrophila from North America that is supposed to have morphologically identical cysts. For a taxonomic treatment including a species assignment of S. cryophila K-1 from Europe within Chloromonas, flagellates will have to be cultivated from cysts or from acquired field material for a detailed morphological description. Acquisition and genetic analysis of cysts that resemble S. cryophila from America could elucidate their relationship to European samples. [ABSTRACT FROM AUTHOR]

Slowly melting snowfields in mountain and polar regions are habitats of snow algae. Orange blooms were sampled in three European mountain ranges. The cysts within the blooms morphologically resembled those of Chloromonas nivalis (Chlorophyceae). Molecular and morphological traits of field and cultured material showed that they represent a new species, Chloromonas hindakii sp. nov. The performance of photosystem II was evaluated by fluorometry. For the first time for a snow alga, cyst stages collected in a wide altitudinal gradient and the laboratory strain were compared. The results showed that cysts were well adapted to medium and high irradiance. Cysts from high light conditions became photoinhibited at three times higher irradiances (600 µmol photons m−2 s−1) than those from low light conditions, or likewise compared to cultured flagellates. Therefore, the physiologic light preferences reflected the conditions in the original habitat. A high content of polyunsaturated fatty acids (about 60% of total lipids) and the accumulation of the carotenoid astaxanthin was observed. They are regarded as adaptations to cope with extreme environmental conditions of snow that include low temperatures, freeze-thaw cycles, and variable light intensity. The intraspecific ability of adaptation of the photosynthetic apparatus to different irradiance regimes seems to be advantageous for thriving in different snow habitats.

Red snow is a well-known phenomenon caused by microalgae thriving in alpine and polar regions during the melting season. The ecology and biodiversity of these organisms, which are adapted to low temperatures, high irradiance and freeze-thaw events, are still poorly understood. We compared two different snow habitats containing two different green algal genera in the European Alps, namely algae blooming in seasonal rock-based snowfields (Chlamydomonas nivalis) and algae dominating waterlogged snow bedded over ice (Chlainomonas sp.). Despite the morphological similarity of the red spores found at the snow surface, we found differences in intracellular organization investigated by light and transmission electron microscopy and in secondary pigments investigated by chromatographic analysis in combination with mass spectrometry. Spores of Chlainomonas sp. show clear differences from Chlamydomonas nivalis in cell wall arrangement and plastid organization. Active photosynthesis at ambient temperatures indicates a high physiological activity, despite no cell division being present. Lipid bodies containing the carotenoid astaxanthin, which produces the red color, dominate cells of both species, but are modified differently. While in Chlainomonas sp. astaxanthin is mainly esterified with two fatty acids and is more apolar, in Chamydomonas nivalis, in contrast, less apolar monoesters prevail. [ABSTRACT FROM AUTHOR]

This paper analyzes data on the state of the pelagic microalgae community of the Kara Sea for all hydrological seasons. The data were obtained during complex in situ observations in 1996-2006. Four phases in the annual succession cycle of the phytoplankton of the nearshore continental area of the Kara Sea were identified: a prevernal phase (cryoflora bloom), vernal phase (ice-edge bloom), summer-fall phase (mixed synthesis phase), and winter phase (dormant phase). These periods are clearly distinguished from each other in their composition of dominating species complexes and quantitative characteristics, i.e., the numbers and biomasses of microalgae. In the investigated region, which is completely covered by ice during most of the year, the primary production processes begin at the same time as in ice-free coastal areas. Growth and blooming of cryoflora occur under the ice cover long before it breaks down. The peak development of the pelagic microalgae community, which is comparable to the spring peak of microalgae in ice-free coastal areas, is observed in the summer, when freshwater runoff from large rivers increases sharply. [ABSTRACT FROM AUTHOR]

The article discusses that snow algae thrive in habitats of melting snow in polar and mountain regions. It mentions that red and orange spherical cysts formed one independent lineage in Chlamydomonadales. It also mentions that ten populations of a species causing orange snow in several mountain ranges in Central Europe.

Melting polar and alpine ice surfaces frequently exhibit blooms of dark pigmented algae. These microbial extremophiles significantly reduce the surface albedo of glaciers, thus accelerating melt rates. However, the ecology, physiology and taxonomy of cryoflora are not yet fully understood. Here, a Swiss and an Austrian glacier dominated either by filamentous Ancylonema nordenskioeldii or unicellular Mesotaenium berggrenii var. alaskanum, were sampled. Molecular analysis showed that both species are closely related, sharing identical chloroplast morphologies (parietal-lobed for Ancylonema vs. axial plate-like for Mesotaenium sensu stricto), thus the unicellular species was renamed Ancylonema alaskana. Moreover, an ecophysiological comparison of the two species was performed: pulse–amplitude modulated (PAM) fluorometry confirmed that they have a high tolerance to elevated solar irradiation, the physiological light preferences reflected the conditions in the original habitat; nonetheless, A. nordenskioeldii was adapted to higher irradiances while the photosystems of A. alaskana were able to use efficiently low irradiances. Additionally, the main vacuolar polyphenol, which effectively shields the photosystems, was identical in both species. Also, about half of the cellular fatty acids were polyunsaturated, and the lipidome profiles dominated by triacylglycerols were very similar. The results indicate that A. alaskana is physiologically very similar and closely related but genetically distinct to A. nordenskioeldii. [ABSTRACT FROM AUTHOR]

The article focuses on snow algae are unique organisms specialized to thrive in melting mountainous and polar snow fields. It mentions that due to their pigmentation, they can reduce surface albedo and thus blooms of cryoflora are believed to foster snow and ice melt during summer. It also mentions that snow and glacial algae are promising candidates to explore the biodiversity of polar and alpine cold ecosystems.

Slowly melting snowfields in mountain and polar regions are habitats of snow algae. Orange blooms were sampled in three European mountain ranges. The cysts within the blooms morphologically resembled those of Chloromonas nivalis (Chlorophyceae). Molecular and morphological traits of field and cultured material showed that they represent a new species, Chloromonas hindakii sp. nov. The performance of photosystem II was evaluated by fluorometry. For the first time for a snow alga, cyst stages collected in a wide altitudinal gradient and the laboratory strain were compared. The results showed that cysts were well adapted to medium and high irradiance. Cysts from high light conditions became photoinhibited at three times higher irradiances (600 µmol photons m−2 s−1) than those from low light conditions, or likewise compared to cultured flagellates. Therefore, the physiologic light preferences reflected the conditions in the original habitat. A high content of polyunsaturated fatty acids (about 60% of total lipids) and the accumulation of the carotenoid astaxanthin was observed. They are regarded as adaptations to cope with extreme environmental conditions of snow that include low temperatures, freeze-thaw cycles, and variable light intensity. The intraspecific ability of adaptation of the photosynthetic apparatus to different irradiance regimes seems to be advantageous for thriving in different snow habitats. [ABSTRACT FROM AUTHOR]