Environmental DNA sampling protocols for the surveillance of marine non-indigenous species in Irish coastal waters

Highlights: • Marine NIS monitoring in Irish waters is crucial to detect invasive species during the early stages of introduction. • The highest number of NIS were found in Dublin and Carlingford as expected for these high invasion risk locations. • Fine mesh tow nets were the most cost-efficient method for surveillance of NIS using eDNA metabarcoding. Understanding the spread and distribution of Non-Indigenous Species (NIS) is key when implementing legislation to maintain good ecosystem health. Environmental DNA (eDNA) has shown great potential to detect aquatic organisms in a rapid and cost-effective way, however their applicability to new environments must be validated prior to their implementation. Here, we tested different field sampling methods in combination with eDNA metabarcoding to develop a tool to detect NIS. Large and small volumes of seawater were filtered, in addition to the collection of sediment and horizontal tow net samples at 12 locations across four distinct geographic areas in Ireland. The biggest dissimilarity in the species recovered was found between sediment and town net samples. Tow nets showed to be the most efficient. A total of 357 taxa were identified, including 16 NIS. Fine mesh tow nets were identified as the most cost-efficient for large-scale monitoring and surveillance of NIS.