Applying eDNA Metabarcoding to assess invertebrate biodiversity of Eelgrass (Zostera marina) meadows across Nova Scotia

Eelgrass (Zostera marina) meadows are a common feature of Atlantic coastlines, forming productive marine communities that are valued for their ecosystem services. Long-term adaptive management of these sensitive ecosystems and effective conservation of the biodiversity they support requires tools to evaluate and monitor patterns of diversity. Environmental DNA (eDNA) metabarcoding is a relatively new approach for estimating aquatic biodiversity, with significant potential for broad-scale monitoring of complex habitats like seagrass communities. In this study, we utilized eDNA metabarcoding to characterize invertebrate biodiversity in eelgrass meadows along a latitudinal gradient in the Northwest Atlantic and compared results to historical surveys of eelgrass in the region. Across 17 sites, 138 metazoan invertebrate taxa were detected with a taxonomic probability assignment > 95%. eDNA was successful at capturing regional patterns of community structure and detecting 20 of 26 common invertebrate taxa based on published records, as well as 80 species not historically recorded. These results emphasize the potential of eDNA to augment eelgrass ecosystem monitoring by enabling efficient, non-invasive cataloguing of biodiversity, including cryptic species that evade conventional sampling.

Methods
Seventeen sites were sampled across approximately 760 km (3.5° of latitude and 6° longitude) of coastline in Nova Scotia, selected based on the presence of eelgrass beds and accessibility. Ten of these sites were sampled from July to September 2019 as part of a study focusing on fish communities within eelgrass beds (He et al. 2022). These sites spanned approximately two degrees of latitude along the coast of mainland Nova Scotia with a focus on the Eastern Shore Islands Area of Interest, an area selected for potential marine conservation area designation (Jeffery et al. 2020). The geographic scope was expanded by additionally sampling six sites in Cape Breton and one on the south shore of Nova Scotia between June to October 2023. Cape Breton sites were sampled across approximately 0.9° of latitude and were located in bays and estuaries on the east and west coasts of the island. Temporal comparisons were not undertaken because there was no overlap in sites between the two years and geographic regions sampled. Instead, data from 2019 and 2023 were combined to explore general geographic patterns in species richness and community composition over a broad latitudinal range.