Ocean acidification (OA), driven by elevated CO2 levels in seawater, negatively impacts economically important marine calcifiers such as Pacific oysters (Crassostrea/Magallana gigas) along worldwide coasts. Increased CO2 interferes with calcification, so oysters are particularly vulnerable when forming their first shell as D-stage larvae. Hatcheries therefore struggle to meet demands for oyster seed due to OA effects on larvae, such as mortality, slow growth, and shell deformities. Hatchery cultivation of seaweed may offer an avenue for seawater remediation: through photosynthesis, macroalgae uptake CO2 from seawater, while providing a range of important products such as nutritious food, cosmetics, and biofuels. To quantify effects and fill knowledge gaps, this study examines the potential for Pacific dulse (Devaleraea mollis) to mitigate OA and the harm it causes on Pacific oyster larvae in land-based co-culture.
The experimental system included three treatments corresponding to ambient (400 μatm CO2), local upwelling (1000 μatm CO2), and projected future upwelling (3000 μatm CO2) OA conditions. Seawater chemistry trials showed that dulse can increase pH by 0.2-0.5 units, depending on OA condition, and can maintain elevated pH under continuous light for at least 20 days (see Fig. 1). Analysis of water samples will show how dulse affects carbonate chemistry across treatments.
Oysters were reared either with or without dulse in each of the three OA conditions. Larvae before and during D-stage at 14, 24, and 48 hours post fertilization (hpf) will be analyzed microscopically for survival, growth, and shell formation. Expression of ion regulation, shell formation, and immune related genes will be analyzed at 48 hpf, demonstrating how relative expression translates to larval condition. Findings will provide useful data for modeling the CO2 uptake potential of dulse seaweed, applicable to industry and restoration efforts for both shellfish and macroalgae. Outcomes of this study can aid the shellfish industry in adapting to climate change while also providing insight into an avenue for crop diversification.