Targeted Metabarcoding to Assess the Possible Effects of Ocean Acidification and Hypoxia in the Olympic Coast National Marine Sanctuary

Olympic Coast National Marine Sanctuary (OCNMS), designated in 1994, encompasses 8257 km² of coastal waters along the Olympic Peninsula of Washington State. Strong upwelling in spring and summer often leads to large, repeated, hypoxic ‘dead zones’ across the OCNMS, accompanied by fish and Dungeness crab die-offs. Pronounced upwelling also is linked to high levels of ocean acidification (OA), with low pH negatively impacting many valuable species, and calcifyingorganisms and larval stages being particularly sensitive. These factors potentially alter community species compositions, relative representation, dynamics, and recruitment. OA and hypoxic conditions are predicted to increase in the coming years, but their impacts on marine communities, fisheries, and MPAs are little known and difficult to predict. To understand their consequences on marine communities, here we evaluate multiple gene metabarcoding high-throughput sequencing analyses of zooplankton net tows and environmental (e)DNA water samples to reference physical and chemical conditions to biological community compositions and diversity in the OCNMS. By designing, testing, and applying several general and specific metabarcode markers, we recover broad phylogenetic representation as well as high species resolution for bioindicator taxa known to be sensitive to hypoxia and OA (pteropods, bivalves, krill, squid, decapods). Multiple years of plankton and water samples taken adjacent to scientific buoys within the OCNMS provide insights into the possible effects of hypoxia and OA on marine communities. We demonstrate that due to low per sample cost, fast turnover, and the flexibility to tailor studies to specific taxa and regions that this approach provides a promising tool for oceanographers and managers to monitor species and communities in marine protected areas.