Alpine Microalgae – ALPALGA

The ALPALGA project focuses on green algae inhabiting high-altitude ecosystems, with particular emphasis on their biodiversity, ecophysiology, and impact on snowmelt dynamics. Analyses will be conducted at sites located near the Col du Lautaret, spanning elevations from 1,000 to 3,000 m. The project benefits from the unique logistical support of a high-altitude research station (Jardin du Lautaret) and brings together experts in mountain biodiversity and biogeography (LECA), algal biology, metabolism and photosynthesis (LPCV), climatic evolution of snow-covered and glaciated environments (CNRM/Centre for Snow Studies), and snow–climate feedback processes in polar environments (IGE). Scientists from the CNRM (Centre for Snow Studies) will contribute to the extraction of key parameters required for the implementation of the SURFEX/Crocus snowpack model.

The results include major advances in the detection of microalgae across altitudinal gradients using environmental DNA, the collection and identification of new species of algae and microscopic fungi, the establishment of living collections subsequently cultivated under laboratory conditions, and the complete genome sequencing of several microalgal species as well as of a snow yeast. Among the most significant outcomes are the elucidation of adaptive traits of the dominant snow alga Sanguina nivaloides at the level of cellular architecture (Nature Communications, 2023), the discovery of the ecological role of the microscopic fungus Phenoliferia psychrophenolica in driving the late-stage dynamics of snow and glacier algal blooms (Communications Biology, 2025), the remote sensing and first large-scale mapping of red snow in the Alps using Sentinel-2 imagery over a five-year period (PNAS, 2024), and the genomic sequencing of several key species (G3: Genes|Genomes|Genetics, 2024, and manuscripts in preparation).

To advance our understanding of snow algae biology through genomic data. To make progress in the study of the spatiotemporal structuring of snow algal populations and associated microbial species, notably through participatory approaches. To elucidate the functional links between cryosphere microbiomes, connected habitats (soils, hydrological networks, atmosphere), and biogeochemical cycles. To clarify the role of these microorganisms in rapidly transitioning mountain environments.

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Microscopic photosynthetic organisms are called ‘microalgae’ or phytoplankton. Their biodiversity is best characterized in aquatic ecosystems. Phytoplankton comprise diverse groups of species within two domains of life, Bacteria and Eukaryota. One group of eukaryotic microalgae, the Chlorophyta (or Green Algae), is remarkable because the majority of species populate land ecosystems, from wet to dry areas, and are even able to occupy the snow cover.

Knowledge on Chlorophyta biodiversity in mountain ecosystem is poor, in spite of the role they are likely to play. Algae are pioneer organisms who can propagate into open areas, such as those left by the retreat of glaciers. As primary producers, they are likely critical in the ecosystems’ dynamics. Due to the lack of reference spatiotemporal study, we are not capable of assessing whether this biodiversity is affected by global climate change. Green algae are usually detected in the snow cover after their proliferation and formation of resistant cells, containing a red carotenoid pigment. The range of Chlorophyta species capable of developing in ‘red snows’ needs to be assessed. Their fate following snow melting and capacity to occupy other habitats are unknown. Furthermore, the presence of algae in the snow has been shown to lower the albedo (reflection of sunlight), accelerating melting.

The ALPALGA project focuses on Green Algae found in high-elevation snow-covered ecosystems, their biodiversity, ecophysiology and impact on the melting dynamics of snowpacks. On site analyses will be performed in long-term survey sites close to the Lautaret pass, from 1,000 to 3,000 m high. The ALPALGA project benefits from the unique logistic support of a high-altitude research station (SAJF) and gathers experts in mountain biodiversity and biogeography (LECA), alga cell biology, metabolism and photosynthesis (LPCV), snow, glaciers and climate evolution in mountain areas (CNRM) and snow-climate feedback processes influencing the fate of ice sheets and other snow covered areas in polar environments (IGE). Experts from CNRM (Snow Research Center) will help translating analyses of snow algae dynamics into parameters implemented in the snowpack model SURFEX/Crocus.

The project addresses three challenges: (1) Evaluating biodiversity in representative mountain habitats and elevation gradients, using environmental DNA; (2) Isolation of life samples for taxonomic, biological and ecophysiological characterization, in relation with high altitude environmental parameters; and (3) Characterizing Green Algae dynamics in the snow cover and capture parameters for implementation in the snowpack model SURFEX/Crocus. The workplan is articulated in four workpackages: (WP1) Environmental DNA and life sampling in representative ecosystems at Vallon Roche Noire and high altitude red snow sites; (WP2), Evaluation of microalgae biodiversity based on DNA markers; (WP3) Cultivation, genomic sequencing and ecophysiological studies in liquid medium of representative taxa of alpine microalgae; and (WP4) Ecophysiological studies in the snow and snowpack model improvement. The project is based on preliminary data supporting the feasibility of the proposed workplan.

Among the major outputs, we expect to establish the first evaluation of the biodiversity of Green Algae in alpine environments, to deduce molecular determinants of algae acclimation and adaptation from comparative genomic and biological studies of alpine species, and provide physiological bases of the settlement of mountain areas by microalgae. The dynamics of snow algae will help improving models predicting climate evolutions and impacts in high altitudes, linked with ecosystem functioning and, in longer terms, functional species networks. Due to the fascinating lifestyle of snow algae and expected advance in knowledge, the dissemination plan includes scientific publications and communication as well as a public outreach program.