Vertebrate impact on bacterial community structure of coastal Arctic spring snowpacks

Abstract. Snow covers up to 35 % of the Earth's surface seasonally, impacts biogeochemical cycling, and forms a microbial habitat despite harsh and variable conditions. While atmospheric deposition is a well-known source of microbial input, the role of vertebrates in shaping snow microbiomes remains underexplored. In Arctic ecosystems, seabirds and terrestrial mammals influence the concentration and distribution of nutrients, but their effects on microbial communities in snow remain poorly understood. Here, we explore the role of vertebrates in shaping snow microbial biodiversity of Arctic terrestrial snowpacks. The study was conducted on the northern coast of Hornsund Fjord on Spitsbergen. Forty snow samples were collected in four transects, two established along the gradient from the centre of a seabird (Alle alle) colony towards non-impacted areas and two transects along the coast. We identified 854 bacterial ASVs using short-read sequencing of the 16S rRNA gene. Samples clustered into four groups based on community composition, but were not linked to spatial factors such as distance to colonies. Bird and terrestrial mammal faecal indicators like Catellicoccus or Streptococcus were detected in 17 out of the 40 samples and drove the formation of two distinct clusters. These findings suggest that coastal Arctic snow microbiomes are strongly shaped by biological activity, with wildlife acting as key microbial vectors.