Evaluating the Potential for Citizen Science Divers to Monitor Fish Biodiversity Through Passive eDNA Collection

ABSTRACT Environmental DNA (eDNA) marker gene sequencing, or metabarcoding, can be a powerful tool for monitoring marine biodiversity. Traditional eDNA sampling methods involve manual water collection and active filtration to collect DNA. This process can be laborious and require expensive filtration equipment. To explore the possibility of making eDNA a more accessible tool, we investigated the efficacy of passive eDNA capture during citizen science SCUBA diving in the Gulf of California, Mexico. Rather than actively collecting and filtering water samples, filters that passively collected eDNA from seawater were attached to citizen scientist divers as they carried out visual surveys on fish species. eDNA metabarcoding from these filters was amplified using MiFish primers (12S rRNA gene) and sequenced to assess fish community composition and compare to visual surveys. We also investigated marine mammal detection with mitochondrial D‐loop metabarcoding primers on some of the samples. Sequencing results initially yielded 64 fish species, compared to 183 fish species observed by the divers, and shared similar biogeographic assemblage patterns. However, 95 visually observed species lacked publicly available reference sequences. To address this, we generated reference sequences for 64 fish species vouchers obtained from the Scripps Institution of Oceanography Marine Vertebrate Collection. Dedicated barcoding efforts yielded eDNA detections of 15 additional species. We discuss the relative advantages and disadvantages of this passive eDNA collection method for marine fish detection. Marine mammal sequencing results only yielded 3 species; however, one was the Guadalupe fur seal, a threatened species, which highlights the potential of eDNA for rare or threatened marine mammal detection. Our results suggest that passive capture of eDNA can be used as a tool for citizen scientists to supplement visual surveys for marine species detection and is particularly useful for species that are rare or visually inaccessible to divers.