Original articleTerrestrial isopods (Isopoda: Oniscidea) as unexpected inhabitants of extreme habitats

- Terrestrial isopods maintain stable populations in the Southern European Đon močvar peat bog.
- Despite prior assumptions, high acidity and low calcium availability are not key limiting factors for woodlice distribution.
- Occurrence of woodlice in Southern European peat bogs is likely related to successional changes and warmer climate.
- Active conservation measures are essential to preserve this fragile ecosystem and its unique soil assemblages.

Peat bogs, naturally acidic environments, are extreme habitats for many soil macroorganisms. Soil acidity and reduced calcium availability strongly affect soil invertebrates, which require calcium to build exoskeletons. Calcium availability is assumed to limit survival of terrestrial isopods in this nutrient-poor environment. Previous studies, though scarce, have shown that isopods are absent from peat bogs in the north Holarctic. Thus, they were sampled using pitfall traps in the largest and oldest Western Balkans (Croatia) peat bog and at its edges. Isopods were found to maintain stable populations in the Western Balkan peat bogs, despite the extreme soil properties. Species richness did not differ between the centre of the peat bog and its edge, however activity density was higher at the edge, implying that edges provide more favourable habitat for isopods based on microclimatic conditions, food availability, and shelter sites. Calcium concentration is not the key limiting factor for isopod distribution in peat bogs as previously assumed. Environmental variables that impacted isopod spatial distribution include soil moisture and vegetation structure. Thus, presence of isopods in Southern European peat bogs is likely related to warmer climate and successional changes in peat bogs.