Annual Cycle of Mat-Forming Filamentous Alga Tribonema cf. minus (Stramenopiles, Xanthophyceae) in Hydro-Terrestrial Habitats in the High Arctic Revealed By Multiparameter Fluorescent Staining

The filamentous microalga Tribonema sp. (Stramenopiles, Xanthophyceae) plays an important role in shallow water polar (streams and seepages) and seasonally cold habitats in temperate regions (ponds). In these habitats, freezing and desiccation, and thus freeze-thawing and drying-rewetting cycles, are frequent. These regions produce visible biomass and are important components of low temperature-adapted communities. We characterized the annual cycles of a Tribonema cf. minus population in two habitats (seepage and stream) in the High Arctic, Svalbard. Seasonality, locality, and their combination (particularly changing environmental conditions) together with cultivation conditions of strains significantly affected their morphological characteristics. Morphological changes following hardening processes related to preparation for the winter period (transition from vegetative cells to akinete and/or pre-akinete) were recorded. Over the year, positive water temperatures (warmest 13.3°C) occurred for 5 months while negative (lowest temperature was -17.4°C) lasted for 7 months. In winter, there were two melt periods. Vitality staining protocol showed a high number of viable (77.4% and 53.8%) and dormant cells (1.7% and 4.1%; capable of growth and reproduction once suitable conditions return) in the winter seepage and stream, respectively. NPQ and OJIP chlorophyll fluorescence parameters revealed several hours recovery of photosynthesis (both field and control samples). During recovery, only minor or mild stress on photosynthesis was detected. F_V /F_M values (the photosynthetic efficiency of photosystem II in a dark-adapted state) in all field and control samples varied around 0.4. Tribonema cf. minus is capable of surviving winter Arctic conditions (perennial strategy).