The Floating Lab: Standard Operational Procedure for Collecting and Filtering Seawater Samples from Operating Ferries for Environmental DNA Analysis.

Genetic tools to retrieve information from environmental DNA traces are well-established for both targeted and taxonomically broad biodiversity characterization. Yet, in the marine context, collecting eDNA samples from poorly accessible areas, such as in abyssal or offshore waters, may still be a limitation. The use of scheduled ferries or commercial ships crossing large expanses of open sea can constitute valuable opportunistic platforms for the collection of environmental samples. The advantages are countless, from the possibility of collecting data in any weather condition and at any time of day to the repeatability over time, being the routes constant, and with a total reduction in costs and fuel emissions. Previous work has shown that the approach is possible and successful. However, the process of acquiring samples from the bellies of these large marine vessels may not be immediate. This work illustrates in every detail how the collection and filtering of seawater from large ships can be prepared, arranged, and carried out.