Global seaweed farming could be a boon, but only if it scales sustainably

The world’s food systems are buckling under increasing pressure. Rising global temperatures, growing demand and unsustainable land use are pushing terrestrial farming to the limit. But off the coast of our overstressed lands lie oceans of untapped potential. New research published in Nature has identified 650 million hectares of ocean – an area almost the size of Australia – suitable for large-scale kelp farming. This burgeoning industry could supplement human diets, feed livestock, create biofuels, slow climate change and provide crucial habitat for a vast diversity of marine life, the study says. It’s enough to make you wonder: Is there anything seaweed can’t do?

The short answer to that question is yes. There are limitations to the impact and scaling potential of seaweed aquaculture, the study’s authors say. “I think they’re just a little harder to see because we are starved for solutions to the climate crisis and biodiversity crisis,” says co-author Scott Spillias, a doctoral candidate studying seaweed farming at the University of Queensland in Australia. Scaling the size and productivity of farms in Western countries, expanding the market for seaweed-based products and reducing environmental risks are just some of the hurdles farmers and entrepreneurs will have to clear. But this research gives us a good idea of just how big the industry could become if it grew to its maximum potential. 

Outside of East Asia, where the industry is already mainstream, commercial seaweed farming is still in its infancy. Although Indigenous communities in the United States have farmed seaweed for generations, most of the West’s commercial seaweed farms have only appeared in recent years. Western seaweed farms look very different from Asia’s mega-farms, which can cover thousands of hectares of ocean and produce millions of tons of seaweed per year. “China is a really great example where you look out onto a bay and it’s seaweed or some sort of aquaculture as far as the eye can see,” says Gretchen Grebe, project coordinator at the Marine Biological Laboratory in Woods Hole, Massachusetts.

While seaweed is the country’s fastest growing aquaculture product, American seaweed farmers produce far less than large-scale Asian farms, according to Danielle Blacklock, director of aquaculture at the National Oceanic and Atmospheric Administration. The American seaweed market is mostly driven by small companies like Montauk Seaweed Supply, a two-year-old startup in the Long Island Sound that partners with seaweed farmers to turn their harvests into biofertilizer, a more environmentally friendly alternative to synthetic fertilizers. However, this is just a niche market for now – unlike the behemoth Asian farms, Grebe says. 

If seaweed farms expand throughout the West, though, the new Nature study suggests the environmental benefits could be tremendous. The researchers modeled the global expansion of large-scale seaweed farming between now and 2050, looking specifically at five theoretical scenarios that consider different levels of seaweed use for human food, livestock feed and biofuel production. 

They found that cultivating red seaweed for livestock feed could reduce annual carbon emissions by 2.6 gigatons, which is equivalent to taking more than 570 million cars off the road for a year. Substituting 10% of human diets with seaweed would spare up to 110 million hectares of land from terrestrial agriculture. And because most biofuels are made from terrestrial crops like corn and sugarcane, using seaweed for biofuel feedstock could offer substantial reductions in fertilizer use, which could significantly reduce nutrient pollution. 

Not all of these payoffs are equally realistic, however. “I think I’d be pretty surprised if any of these scenarios happen in the [2050] timeframe,” Spillias says. Getting humans to increase their seaweed consumption by 10% globally poses a particular challenge. In East Asia, seaweed is a staple ingredient, but even there it only makes up 2% of the average person’s diet, he says. Increasing seaweed consumption in the West significantly beyond consumption levels in Asia would require a massive cultural shift. 

That’s why Montauk Seaweed Supply still focuses on using kelp to create fertilizer rather than food for the time being, says Sean Barrett, a co-founder of the company. Over a decade of experience working in the commercial seaweed industry showed him the challenges of marketing seaweed-based food products to US consumers. Three years ago, he pivoted to seaweed fertilizers instead. “We were meeting a good amount of resistance – Americans are not really accustomed to eating macroalgaes,” he says.

Experts point to significant hurdles for biofuel adoption, too. The first is seaweed availability. “The amount [of seaweed] that needs to be produced to make it economically viable to do biofuels is a scale that we have not come close to in the United States,” says NOAA’s Blacklock. The second hurdle is cost. The Marine Algae Industrialization Consortium, a project of Duke University, is working to create an algae-based biofuel that can sell for around $5 per gallon. But even at that lower price, seaweed fuels would likely fail to compete with ethanol, which is currently priced at $2.16 per gallon. 

While scaling global seaweed farming could have several environmental benefits, expanding it at the rate outlined by Spillias’ study raises questions about potential environmental risks, too. Preventing the proliferation of invasive seaweeds is of particular concern for farmers and business owners. There is a “raging” debate within the seaweed-farming community as to whether farmers can sustainably cultivate seaweeds that are not native to their region, explains Montauk Seaweed’s Barrett. As the industry expands, “farmers are wanting to grow different types of crops,” he says. While it can be tempting for farmers to import non-native species to diversify their yield, this can harm the local ecology. For example, growing California’s bull kelp in New York, where sugar kelp is the dominant native species, could lead to competition for space and resources between the two species and threaten native sugar kelp populations, Barrett says.

In addition to considering the impact of proliferating non-native seaweeds, NOAA’s meticulous vetting system evaluates the suitability of seaweed farming sites in part by ruling out locations where endangered species, threatened habitats or corals are present. This siting process “is everything,” Blacklock says. Introducing seaweeds to an area where the ecosystem is already stressed, like a coral reef, can increase the strain on critical resources like nutrients, sunlight and space. 

“You can’t just plop a farm down anywhere,” says the Marine Biological Laboratory’s Grebe. But sometimes, seaweed farms can actually be a boon for the local environment – and economy. After Grebe’s kelp farm was established, hundreds of Caribbean spiny lobster flocked to the newly generated habitat, making a home for themselves from the research site. These lobsters are a coveted catch for local fishers, which may generate new economic opportunities in a place that previously would not have been fished, Grebe says. Siting is important not just for reducing environmental harm, but also for maximizing a kelp farm’s services to the surrounding community. 

While models like Spillias’ can offer a big-picture perspective on how seaweed aquaculture could scale, actually bringing this industry to a global scale – sustainably – will require many more years of research, entrepreneurship and cultural change, according to Spillias. 

“I don’t want us to make the same mistakes in the ocean that we’ve made on land,” Spillias says. 

Correction: An earlier version of this article stated that Sean Barrett of Montauk Seaweed Supply became interested in seaweed after working in the food industry three years ago, and then pivoted to seaweed-based fertilizer. This statement has been corrected to more accurately reflect the timeline of his experience in the commercial seaweed industry. Updated May 18, 2023.