A breath of fresh air: comparative evaluation of passive versus active airborne eDNA sampling strategies

The rapid decline of terrestrial biodiversity worldwide demands for expansion of high-resolution biomonitoring to support science-based policy. Environmental DNA (eDNA) analysis has proven effective at biomonitoring aquatic systems but remains underexplored for terrestrial habitats, partly due to point-source sampling bias and difficulty in upscaling. Air has recently emerged as a promising substrate for terrestrial biomonitoring yet most studies use active samplers which tend to be expensive, bulky, and require power. We used a newly developed, inexpensive, reusable, and easy-to-use passive airborne eDNA sampler (DNAir Sampler) to capture eDNA suspended in air over 96 hours within Rotterdam Zoo, the Netherlands. Its performance was compared to two commonly used active airborne eDNA samplers for vertebrate diversity detection. In total, 88 species were detected, including 24 zoo residents. The DNAir Sampler was the most effective at detecting zoo residents, surpassing active samplers in species richness within 48 hours and continuing to accumulate new species beyond 96 hours. It also detected the furthest species signal (515m). Zoo airborne eDNA further demonstrated a positive correlation to species total biomass. Our findings indicate that for long, un-supervised biomonitoring, passive airborne eDNA sampling outperforms active sampling for assessing vertebrate communities and potentially reduces detection noise in stochastic air eDNA signals.