Do acidic habitats act as chytrid refugia? Preliminary insights from Lutruwita amphibians

Context The chytrid fungus Batrachochytrium dendrobatidis has driven global amphibian declines, but environmental conditions modulate disease risk, population persistence and recovery. Environments not well suited to B. dendrobatidis can act as ‘pathogen refugia’ for frog populations and are important for frog conservation. Although salinity and temperature refugia are known, the role of acidic waters in suppressing B. dendrobatidis remains unclear. Laboratory studies show that B. dendrobatidis growth is inhibited below pH 6.0, but field data from highly acidic habitats (pH < 5.0) are scarce. Aims We conducted an exploratory, hypothesis-generating study to assess whether naturally acidic aquatic habitats in Western Lutruwita–Tasmania function as partial refuges from B. dendrobatidis for acid-tolerant amphibians, particularly the B. dendrobatidis-sensitive Tasmanian tree frog (Saganura burrowsi). Methods We combined calling surveys and swab-based B. dendrobatidis testing of tadpoles and adults across pH gradients in buttongrass moorland pools. Data were complied from several long-term conservation programs, resulting in uneven sampling across sites, species and life stages. Key results Multiple frog species, including the endemic S. burrowsi, were observed breeding in waters as acidic as pH 4.1. B. dendrobatidis was detected in tadpoles at pH 4.1–4.8, among the lowest field detections reported to date. Adult frogs also tested positive in acidic habitats, but with no visible signs of chytridiomycosis. However, infection probability was lower at lower pH. Conclusions Despite limitations of our dataset, with uneven sampling across sites, species and life stages, our observations are consistent with the hypothesis that highly acidic waters provide partial refuge from B. dendrobatidis. Further targeted standardised sampling is required to test effects on prevalence. Implications We identify three areas for future investigation: (1) pH-mediated B. dendrobatidis refugia, (2) physiological trade-offs, and (3) life-stage susceptibility with potential carryover effects.