Meta‐analysis supports further refinement of eDNA for monitoring aquatic species‐specific abundance in nature

The use of eDNA to detect the presence/absence of rare or invasive species is well documented and its use in biodiversity monitoring is expanding. Preliminary laboratory research has also shown a positive correlation between the concentration of species‐specific eDNA particles and the density/biomass of a species in a given environment. However, the extent to which these results can be extended to natural environments has yet to be formally quantified. We collated data from experiments that examined the correlation between eDNA and two metrics of abundance (biomass and density) and, using mixed‐effects meta‐analysis, quantified the strength of that correlation across laboratory and natural environments. We found that eDNA particle concentration was more strongly correlated with abundance in laboratory environments compared to natural environments, accounting for approximately 82% and 57% of the observed variation in abundance, respectively. We found some evidence of potential publication bias that may have impacted the estimation of the correlation in natural environments; after smaller studies were removed from the dataset, eDNA particle concentration accounted for approximately 50% of the observed variation in abundance in natural environments. No effect of abundance metric was found on the strength of correlation between eDNA particle concentration and abundance. Despite a weaker general correlation in natural environments, eDNA concentration often still explained substantial variation in abundance. eDNA research is still an emergent field of study; with only moderate improvements in technology or technique, it could represent a powerful new tool for quantifying abundance.