Morphological and phylogenic variability of red snow algae in snowpacks along a glacial valley in Alaska

Abstract. Red snow blooms are visually similar but can be composed of different algal species and cell morphologies across sites, and the factors determining this spatial heterogeneity remain poorly understood. In this study, we investigated spatial variation in community structure, algal cell size, and morphology along gradients of elevation across a glacier and its forefield in Alaska. Microscopic observations revealed that the ice-based snowpack was dominated by spherical cells, whereas the soil-based snowpack was characterized by a higher abundance of non-spherical cells and larger spherical cells. Molecular analyses revealed that Sanguina predominated in the ice-based snowpack, while the relative abundance of other genera, including Chloromonas and Rosetta, were more abundant in the soil-based snowpack. Redundancy analysis showed that community structure was explained primarily by snow depth and elevation, whereas it was not significantly influenced by nutrient concentrations. Generalized linear models further indicated that size of spherical cell decreased with elevation, and the proportion of non-spherical cells decreased with snow depth. These results suggest that while snowmelt-driven environmental gradients govern the overall morphological and phylogenetic variability of red snow algae, the underlying substrate (ice vs. soil) also contributes to community turnover, likely by providing access to distinct local cell reservoirs during melt progression. Collectively, these factors shape the taxonomic composition, morphotype assemblage, and spatial development of red snow blooms.