Deep and shallow subterranean habitats connect Collembola communities in iron ore deposits

Subterranean ecosystems are recognized reservoirs of biodiversity, yet shallow subterranean habitats (SSHs) remain poorly understood. SSHs form transitional environments between surface and deeper subterranean zones and may play a role in structuring and connecting subterranean fauna. We investigated whether shallow and deep subterranean habitats facilitate connectivity among Collembola communities within ferruginous deposits in Brazil. We sampled Collembola communities over two years with baited traps at multiple depths (3–41.9 m) in boreholes drilled into ferruginous formations across two mountain ranges. A total of 76,326 individuals representing 8 families, 20 genera, and 25 species were collected. Species richness varied significantly between mountain ranges and sampling periods, but not with depth or lithological profile. In contrast, total abundance and community composition were strongly structured by time, depth, and substrate, with significant interactions indicating vertical and temporal stratification. Community-level analyses revealed that depth and lithology influenced species turnover, while the presence of epigean species alongside subterranean taxa suggests connectivity and ongoing ecological exchange between surface, SSH, and deeper subterranean habitats. SSHs and deeper subterranean habitats form an integrated ecological continuum rather than discrete systems, supporting the hypothesis that SSHs provide connectivity to surface and cave-like environments. Given the biotic and abiotic particularities, SSHs landscapes require specific approach in subterranean biodiversity conservation and environmental impact assessments, mainly in iron ore formations.