Mapping Biodiversity Coast-to-Coast-to-Coast Across Canada's Three Oceans Using eDNA Metabarcoding

Marine biodiversity worldwide is rapidly declining, and nowhere is this more evident than in coastal ecosystems where the impacts of climate change and anthropogenic activities concentrate. The ongoing biodiversity crisis affects all components of the marine food web, but data required to monitor biodiversity shifts at continental scales are scarce and taxonomically and spatially heterogeneous. The application of environmental DNA metabarcoding can complement traditional approaches to monitoring marine biodiversity, but its efficiency in detecting large-scale biogeographic breaks remains to be tested. Using 86 coastal surface water samples collected during the Canada C3 expedition in the summer of 2017, we investigated metazoan biodiversity across Canada's three oceans—North Pacific, Arctic and North Atlantic—using multi-marker eDNA metabarcoding. The resulting dataset, combining information from seven separate amplicons, identified 1477 unique species ranging from zooplankton to marine mammals. We found that marine coastal biodiversity around Canada separated into four clusters that overlapped with known marine ecoregions, indicating a higher connectivity between the Arctic and Atlantic than between the Arctic and Pacific clusters. However, the detection of Pacific salmon eDNA in the Canadian Arctic suggests that these species may be extending their Pacific distribution range poleward. By comparing the distribution of eDNA with species occurrence recorded in the Ocean Biodiversity Information System (OBIS) for Canada and Alaska coastal waters, we identified 324 “unexpected” species. These results demonstrate the importance of primer selection for species-specific applications of eDNA metabarcoding and provide a benchmark for further work aimed at validating species identification and map species distribution at large spatial scale. Our results showed that eDNA metabarcoding is a powerful method for monitoring biodiversity shifts at an interoceanic scale. Integrating eDNA into monitoring programs can provide valuable insights into biodiversity changes associated with climate change and contribute to filling gaps in the distribution of species-at-risk.