A sea-to-soil solution for the green tides threatening shellfish aquaculture: conceptual model and lessons learned from a pilot project.
Collier SM, Buckner E, Capizzi NJ, Chadsey M, Collins DP
Soil Health
Seaweed pulled off oyster beds and spread on garden soil could close the nutrient loop between ocean and farm — the same minerals choking coastal waters might otherwise be feeding next season's vegetables.
Every summer, thick mats of green seaweed smother shellfish beds on Pacific Northwest beaches, suffocating oysters and fouling equipment. Farmers have to remove it by hand but had nowhere useful to put it — so it just rotted on the beach, releasing pollutants back into the water. This project tested whether that 'problem' seaweed could instead be hauled to farms and spread on fields as a fertilizer and soil builder, benefiting both the coast and the land at the same time.
Key Findings
Decomposing Ulva left on tideflats releases carbon and nutrients back into coastal waters, worsening local ocean acidification and eutrophication — deliberate harvest breaks this cycle.
The pilot successfully established harvesting logistics and cross-sector networks connecting shellfish growers with land-based farmers, demonstrating operational feasibility.
Key challenges identified include managing undesirable substances in harvested seaweed, optimizing application timing and method, and navigating the complex stakeholder relationships inherent in applied coastal-agricultural research.
chevron_right Technical Summary
Researchers piloted a 'sea-to-soil' program that harvests nuisance green algae (Ulva) from shellfish farms and applies it as a soil amendment on land-based farms, turning a coastal pollution problem into an agricultural resource while reducing ocean acidification and nutrient overload.
Abstract Preview
Seaweeds of the genus Ulva form massive blooms known as green tides, which threaten coastal ecosystems and livelihoods. In the Pacific Northwest, seasonal Ulva blooms coat commercial shellfish beds...
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