“Restorative aquaculture” potential greatest in North Sea, East China Sea, and Southern California

Combined commercial shellfish and seaweed aquaculture have significant potential to provide sustainable food and jobs while restoring marine ecosystems in Europe's North Sea, the East China Sea, and Southern California.

A new study published in PLOS ONE finds that every inhabited continent has marine regions well-suited for the kind of shellfish and seaweed aquaculture that benefits both ecosystems and people by filtering polluted waters, providing habitat for commercially valuable species, and generating steady food and jobs. For shellfish, the potential was greatest in Europe, Oceania, and North America, while for seaweed, it was greatest in Europe, Asia, Oceania, and South America.

The North Sea region of Europe, in particular, suffers from significant nutrient pollution, wide-scale loss of shellfish reefs and heavy fishing pressure – making the region a high-opportunity location for restorative aquaculture, the study finds. Other regions, such as the East China Sea, already have robust shellfish and seaweed aquaculture industries, but the study notes ways those regions could improve aquaculture practices to optimize ecological benefits.

Southern California currently has virtually no existing bivalve or seaweed aquaculture operations, but could benefit from them environmentally, the report found.

"Many shellfish and seaweed farms around the world already provide some degree of ecological benefit, but farming operations generally have not been optimized or intentionally designed to provide maximum ecological value," Robert Jones, the global aquaculture lead at The Nature Conservancy, which partnered on the study, told SeafoodSource.

The authors created a global Restorative Aquaculture Index by combining key environmental data, such as nutrient pollution levels, with socioeconomic information, such as quality of governance, and human health factors, such as prevalence of wastewater treatment. The study aims to provide insights to governments, international development organizations, and investors about where to prioritize aquaculture efforts.

Many bivalve shellfish and seaweed species absorb nutrients from surrounding waters, improving water quality and clarity, while mussel, clam, and oyster aquaculture can provide habitat for fish species. At the same time, seaweed can mitigate the local effects of increased ocean acidity by taking up carbon dioxide through photosynthesis. Biologically, oyster reefs, seagrass beds and kelp forests are habitat-forming ecosystem engineers, but have suffered worldwide due to nutrient pollution, over harvesting and other human activities; one 2011 study found that 85 percent of oyster reefs have been lost globally in the last two centuries.

In parts of North America, aquaculture’s benefits are unrealized because an inefficient and unclear permitting process is constraining the aquaculture industry, while neglecting to account for the potential positive impacts of restorative aquaculture, Jones said.

The tide is beginning to turn in the Chesapeake Bay, where oyster aquaculture has been recognized for its nitrogen removal benefits under the Environmental Protection Agency’s nutrient management plan.

“[This] could pave the way for farmers to be compensated monetarily for the ecological benefits they provide through nutrient trading programs,” Jones said.

But not every place can host restorative aquaculture. In some parts of the developing world, a lack of regulatory control is undermining aquaculture’s potential ecological benefits and governments don’t have the capacity to develop, implement, or enforce sound policies. And, some places just aren’t suitable for aquaculture development, such as regions lacking wastewater treatment infrastructure, or places where heavy metals or persistent organic pollutant concentrations are elevated.

"Siting within eco-regions is essential to ensure that shellfish and seaweed that are produced through aquaculture are safe for human consumption – for example, aquaculture should not occur within areas adjacent to wastewater treatment outfalls, (or) major industrial areas where harmful pollutants are entering water bodies," Seth Theuerkauf, an aquaculture specialist at The Nature Conservancy and co-author on the study, told SeafoodSource.

The Nature Conservancy is working on projects that evaluate the best gear types and growing practices that will aid ecosystem recovery, including with Taylor Shellfish Farms in Washington and Island Creek Oyster Company in Massachusetts.

The study was a collaborative effort between scientists at The Nature Conservancy, the National Oceanographic and Atmospheric Administration's National Centers for Coastal Ocean Science and the University of Adelaide.

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