Environmental DNA analysis needs local reference data to inform taxonomy-based conservation policy:A case study from Aotearoa / New Zealand

Effective management of biodiversity requires regular surveillance of multiple species. Analysis of environmental DNA by metabarcoding (eDNA) holds promise to achieve this relatively easily. However, taxonomic inquiries into eDNA data need suitable molecular reference data, which are often lacking. We evaluate the impact of this reference data void in a case study of fish diversity in the remote fiords of New Zealand. We compared eDNA-derived species identifications against Baited Remote Underwater Video (BRUV) data collected at the same time and locations as the eDNA data. Furthermore, we cross referenced both eDNA and BRUV data against species lists for the same region obtained from literature surveys and the Ocean Biodiversity Information System (OBIS). From all four data sources, we obtained a total of 116 species records (106 ray-finned fishes, 10 cartilaginous fishes; 59 from literature, 44 from eDNA, 25 from BRUV, 25 from OBIS). Concordance of taxonomies between the data sources dissolved with lowering taxonomic levels, most decisively so for eDNA data. BRUV agreed with local biodiversity information much better and fared better in detecting regional biodiversity dissimilarities. We provide evidence that eDNA metabarcoding will remain a powerful but impaired tool for species-level biodiversity management without locally generated reference data.