Tracking an invasion front with environmental DNA

Data from environmental DNA (eDNA) may revolutionize environmental monitoring and management, providing increased detection sensitivity at reduced cost and survey effort. However, eDNA data are rarely used in decision-making contexts, mainly due to uncertainty around (1) data interpretation and (2) whether and how molecular tools dovetail with existing management efforts. We address these challenges by jointly modeling eDNA detection via qPCR and traditional trap data to estimate the density of invasive European green crab (Carcinus maenas), a species for which, historically, baited traps have been used for both detection and control. Our analytical framework simultaneously quantifies uncertainty in both detection methods and provides a robust way of integrating different data streams into management processes. Moreover, the joint model makes clear the marginal information benefit of adding eDNA (or any other) additional data type to an existing monitoring program, offering a path to optimizing sampling efforts for species of management interest. Here, we document green crab eDNA beyond the previously known invasion front and find that the value of eDNA data dramatically increases with low population densities and low traditional sampling effort, as is often the case at leading-edge locations. We also highlight the detection limits of the molecular assay used in this study, as well as scenarios under which eDNA sampling is unlikely to improve existing management efforts.

Automated summary

Data from environmental DNA (eDNA) has the potential to revolutionize environmental monitoring and management by increasing detection sensitivity and reducing cost and survey effort. However, the use of eDNA data in decision-making is limited due to uncertainty in data interpretation and uncertainty in how molecular tools align with existing management efforts. This study addresses these challenges by jointly modeling eDNA detection and traditional trap data to estimate invasive green crab density. The findings highlight the value of eDNA data in low population density and low traditional sampling effort situations, but also demonstrate the detection limits and scenarios where eDNA sampling may not improve existing management efforts.