Assessing distribution of Didemnum vexillum in Scotland using environmental DNA

Conclusions

The present pilot study demonstrates the potential of eDNA-based surveys to rapidly acquire data on the potential presence of priority marine NIS, such as D. vexillum, across large geographic areas. It is not yet clear how exactly eDNA data will be used for the assessments of Good Environmental Status under national and international obligations; however, in the first instance, eDNA can be used to target traditional, physical NIS surveys by cost-effectively selecting sites of greater concern. The simple instrumentation needed to collect water samples for eDNA-based monitoring means that future sampling of water samples can be carried out by a wider pool of scientific staff and/or trained citizen scientists, thereby significantly reducing resources while expanding geographical coverage.

The study indicated a good concordance between presence of D. vexillum found during traditional RASs and that inferred from detection of D. vexillum eDNA in water samples. Additionally, this study showed that detection of eDNA could be used to guide traditional NIS monitoring approaches in a cost-effective way.

To further unlock the potential of eDNA-based monitoring, there is a need to build up from the single species-targeted approach to simultaneous detections of a number of marine NIS in a single reaction. A metabarcoding approach has already been demonstrated as a powerful tool for potential use in the monitoring of marine NIS (for example, von Ammon et al., 2018; Holman et al., 2019; Rey et al., 2019) and this would further improve the cost-effectiveness of using DNA-based tools. Additionally, as metabarcoding allows for simultaneous monitoring across multiple trophic levels (D’Alessandro and Mariani, 2021; Blackman et al., 2022), this tool might have a potential to measure potential environmental impact of marine NIS which cannot be truly delivered using the traditional survey approaches.