230911_abstract.txt

Effective biodiversity management requires regular surveillance of multiple species. Analysis of environmental DNA (eDNA) holds promise to achieve this relatively easily. However, taxonomy-focussed eDNA surveys need suitable molecular reference data, which are often lacking, particularly at the species level and for remote locations. To evaluate the comparability of eDNA and traditional surveys in a real-life case study of a marine area of high conservation value, we conducted a biodiversity survey of the fish in remote and pristine Te Wāhipounamu / Aotearoa, incorporating multiple data sources. We compared eDNA-derived species identifications against Baited Remote Underwater Video (BRUV) collected at the same time and locations as eDNA. We also cross-referenced both eDNA and BRUV data against literature and the Ocean Biodiversity Information System (OBIS), with literature and OBIS data representing a summary of multiple traditional surveying approaches. We found 116 fish species. Environmental DNA detects 43 species, however only three of those species overlap with species known from the literature, OBIS or BRUV analyses. A total of 61 fish species were known from the region from  literature, while OBIS lists 28 species, and our BRUV analyses picked up 26 species. BRUV data coincided more strongly than eDNA data with literature and OBIS data. Twenty of the 26 species detected by BRUV were known from literature and OBIS. We argue that limitations in DNA reference databases are the main drivers of this discrepancy, and our results indicate that eDNA of rare and endangered species can be detected if reference data was available. Environmental DNA analyses can only identify species present among reference data and may converge on relatives of detected species if the detected species themselves are missing therein. However, we confirm  that eDNA could be a powerful tool for biodiversity surveys if suitable investments in local reference databases were made.