Abstract Glacier mice are spherical‐to‐ovoidal bryophyte structures forming and growing on ice surfaces, making them a peculiar type of glacial habitat. They may host different assemblages of specialist invertebrates compared with habitats further downstream. In this study, we investigated the diversity and composition of invertebrate communities inhabiting glacier mice, as well as comparing the latter to fauna found in other glacial and non‐glacial habitats. We collected samples of bryophytes from glacial (the glacier ice surface and a medial moraine) and proglacial environments (the glacial forefield), as well as from glacier sediments (cryoconite) at Austerdalsbreen, Norway. The fauna was identified by applying a classical (microscopic) approach combining the knowledge of various taxonomic experts and a molecular (metabarcoding) approach. Glacier mice consisted of the two bryophyte species Racomitrium fasciculare and R. ericoides . The invertebrate diversity of the glacier mice comprised Tardigrada, Rotifera, Acari, Collembola, Coleoptera, Diptera, and unidentified Nematoda and Psocoptera. In total, we found 94 species, of which 39 were found in glacier mice from the glacier ice surface. Although the diversity of invertebrates in glacier mice was lower than in the proglacial environment, we identified specialists in glacier mice on ice such as the tardigrade Fontourion glaciale , the beetle Helophorus glacialis , and the springtail Agrenia bidenticulata . The composition of Rotifera overlapped between the glacial and proglacial environments, while it differed for other groups. Joint species distribution analyses revealed that Rotifera, Tardigrada, and Collembola commonly occurred in glacier mice on ice surface habitats, whereas the probability of Acari occurrence was highest in the proglacial environment. No major differences were observed in higher taxonomic group‐based community compositions of invertebrates (alpha and beta‐diversity indices) across ecosystems. Our results show that glacier mice in Norway can be inhabited by both opportunistic and specialist fauna. Thus, glacier mice may act as refugia, depending on climate fluctuations.
Zawierucha et al. (Fri,) studied this question.