Glaciers are increasingly recognised as ecosystems in their own right, yet the ecological processes underpinning life on ice remain poorly understood. In particular, we lack detailed knowledge of supraglacial biodiversity, population structures, trophic interactions, and the fluxes of energy and matter that sustain these extreme habitats.

Here, we present the first insights into the ecological networks of two Italian glaciers: Forni (in Stelvio National Park) and Mandrone (in Adamello Regional Park), both located in the Central Alps. Using an integrated suite of morphological and molecular tools—including DNA barcoding, environmental DNA (eDNA) metabarcoding, population genetics, and stable isotope analysis—we characterised community composition and reconstructed food web structures.

To date, we have identified over 683 taxa on Forni and more than 656 on Mandrone, encompassing bacteria, protists, fungi, mosses, tardigrades, and arthropods. Our results reveal simple but structured ecological networks, driven by allochthonous organic inputs and local primary production, mainly by Cyanobacteria. In both glaciers, tardigrades (e.g., Cryobiotus klebelsbergi) dominate the communities of cryoconite holes (small ponds on the glacier surface). On Forni, a more complex trophic cascade connects springtails (Collembola) to predatory beetles (Nebria spp.) and spiders (Linyphiidae, Pardosa spp.), besides non-biting midges (Chironomidae) in the bedieres, highlighting the emergence of higher-order interactions. In contrast, Mandrone supports a less articulated supraglacial web.

These findings underscore both the ecological value and the vulnerability of glacier-associated networks, which are rapidly shrinking under climate change. The results have direct implications for conservation planning: glacier ecosystems are listed among priority habitats under the EU Habitats Directive (92/43/EEC, code 8340), and our data contribute to defining conservation targets and future monitoring strategies for these vanishing environments.