A novel drop-sampler for simultaneous collection of stereo-video, environmental DNA and oceanographic data

Context; There is an increasing interest in environmental DNA (eDNA) as a method to survey marine biota, enhancing traditional survey methods, and a need to ground truth eDNA-based interpretations with visual surveys to understand biases in both the eDNA and visual datasets.Aims; Design and test a rapidly-deployable, robust method pairing water sampling for eDNA collection and stereo-video imagery, and compare inferred fish assemblages with interspersed baited remote underwater video (stereo-BRUV) samples.Methods; We augmented a wide-field stereo-video BOSS drop camera with Niskin bottles to collect water samples from the seabed, enabling the comparison of paired eDNA and stereo-video based assessments of fish assemblages. The platform demonstration was conducted in proximity to a submerged ancient coastline feature in the no-take National Park Zone of the Ningaloo Marine Park, and complemented with interspersed stereo-BRUV samples.Key results; The system is capable of simultaneously collecting 270 degree stereo-video imagery, oceanographic measurements and water samples for eDNA, across a range of habitat and depths (up to 600m). Combining simultaneously acquired visual survey data with eDNA species estimates increased the total diversity of the fish assemblage by ca. 20% over eDNA estimates alone, whilst the assemblage composition sampled by each method was significantly different.Conclusions; We have demonstrated a single sampling platform that can cost-effectively collect spatially-discrete and simultaneous eDNA, stereo imagery and oceanographic data.Implications; Our platform demonstration highlighted the biases of each sampling method. We suggest that these biases will be better understood by advancements that allow eDNA metabarcoding to discriminate the abundance and life-stage of marine biota. Furthermore, investigation of the relationship between metabarcoding data and concomitant imagery-derived length, age and habitat data are needed.