1 Introduction Groundwater ecosystems—including aquifers, cave systems and their biological communities—constitute the world's largest freshwater biome (Mammola et al. 2019). These subterranean environments support high-value, complex, and biodiverse communities of animals and microbes (Marmonier et al. 2023) (Box 1) which provide essential ecosystem services that maintain healthy freshwater resources (Griebler and Avramov 2015; Griebler et al. 2019; Saccò et al. 2025). Mammola et al.
