Seaweed Farming: Silver Bullet or Something Else?

Seaweeds have become increasingly popular in recent years. As more eyes are drawn to farming them, are we dealing with a promising untapped resource or are there some potential downsides to consider?

Seaweeds are far more than just slimy algae that wash up on our beaches. They are also a good source of proteins, vitamins, minerals, dietary fibre, a promising plastics alternative, and an eco-friendly cow feed.^1,2,3

Now, there is a surge of interest in seaweed farming, especially in the US and Europe. FAO estimates show that between 2015 and 2020, seaweeds accounted for 51% of global mariculture production at 35.1 million tonnes live weight.⁴ And while Asian markets still produce over 95% of the world's seaweed, production is quickly expanding, with Alaska, Maine, France and Norway more than doubling their seaweed production since 2018.⁵ There is also good reason to farm seaweed from a climate perspective. It could reduce our global agricultural greenhouse gas emissions (GHG) by up to 2.6 billion tonnes of CO2-equivalent per year, for example if it’s included in cattle feed to reduce methane emissions from cattle.⁶ It can also absorb wave energy, safeguard shorelines, oxygenate waters, and help to minimise the impacts of ocean acidification.⁷

However, there are still a few issues that hinder the growth of seaweed production, such as scalability, sustainable growth, public education and awareness, and making the cost of production competitive, according to Rhianna Rees, Business Development Manager at the Scottish Seaweed Industry Association (SSIA), which is working to resolve these issues in Scotland. Rees says that the focus on seaweeds comes down to their potential uses.

"By this, we mean seaweed’s versatility as a highly nutritious food source, a sustainable fertiliser, a low-carbon animal feed and its role in the development of single-use plastics alternatives,” she said. “The increasing interest in seaweed farming is also being driven by an understanding that wild-harvested seaweed alone cannot keep up with rising demand.”

Vincent Doumeizel is senior advisor at the United Nations Global Compact on Oceans and director for the Food Programme for the Lloyd's Register Foundation. He is also the author ofThe Seaweed Revolution. In it, he states that the potential of seaweeds to transform our world is huge, and that if grown sustainably, they could feed people, replace plastic, decarbonise the economy and even restore biodiversity in our ocean.

China is one of the only countries that have realised industrialised seedling raising, large-scale offshore cultivation, and mechanised harvesting, forming an industrial chain from product processing to sales. Lianyungang City, China, 2020. Photo by Costfoto via Getty Images.

Is seaweed farming all that it seems?

While Doumeizel is optimistic, he is also aware of the unknowns of farming seaweeds.

"We don't know well how to cultivate them in the North Atlantic," he said. "The big question is not what we grow, but how we grow it. Seaweeds are also associated with problems like invasive species, for example Sargassum, which has been invading the Caribbean. They can be seen more as a problem than a solution. The idea is to do something better, but it will take time and we need more science."

Evidence suggests that seaweed farms can drive a number of other negative impacts, according to Nick Hill, co-founder and CEO of social enterprise Coast 4C. Risks to farmers are high due to outdated farming technologies, water use conflicts, and climate change, which brings with it multiple specific threats related to seaweed health, disease, and loss of natural seaweed habitats where farmed production is taking place.⁸ Much like rice, coffee, and cocoa, the nature of seaweed production means it is also better suited to hands-on smallholder production - reflected by the ~80% of the global seaweed crop coming from smallholders. While this offers smaller communities and local producers the opportunity to benefit from the industry, the smaller scale of production and profits can magnify the impacts of these risks. 

As a result, farmers are opportunistic and often reinvest their income from seaweed into fishing even as fish stocks decline. Meanwhile, without careful site selection, seaweed farms can lead to less fish abundance by negatively affecting the biological and physical structure of environments such as shallow coral reefs. This, in turn, may result in decreases in fish abundance and biomass.⁹ As with many other industries, high levels of risk also tend to further perpetuate unsustainable practices, such as opting for single-use plastics that are cheap to buy, chopping mangroves for planting materials and habitat simplification such as coral removal. Seaweed farming can be done positively, Hill says, but it must be managed purposely with a holistic view.

In Haizhou Bay, fishermen unload fresh seaweed from a boat. Porphyra, also known as nori Nei, have become the most widely farmed seaweed species in China, with a culture area accounting for over one half of all the farmed seaweeds. Lianyungang City, China 2022. Photo by Wang Chun via Getty Images.

Industry bottlenecks

Thierry Chopin, phycologist and aquaculture professor at the University of New Brunswick, Saint John, Canada, says that the technologies for harvesting and drying seaweeds, which have a direct impact on product quality, are two bottlenecks for the growth of the industry and could be made more environmentally friendly and efficient with more research and development.

Another issue is the notion of sinking seaweeds as a means to sequester carbon. This involves growing large amounts of seaweed and burying it at the bottom of the ocean as a carbon removal strategy. Research suggests that when seaweeds die and sink to the sea floor, they bring significant amounts of carbon with them.¹⁰ However, we know very little about the risks. In a paper soon to be published, Chopin and 19 co-authors characterise deep-ocean seaweed dumping as questionable, risky and not the best use of valuable biomass. "Furthermore, if you want to grow seaweeds on a large-scale, you will have to move offshore, which is less nutrient-rich than coastal waters. This could limit seaweed growth," said Chopin.

According to Rees, "Fully understanding the seaweed lifecycle is extremely important for carbon accounting, because the lifecycle doesn't end when the seaweeds are sunk. Depending on how deep they go, they are consumed by microorganisms on the seabed and we don't know the effects of this. We need to understand more about the activities and monitoring that need to happen and their impacts."

Finally, scaling up production hinges heavily on local knowledge. Whilst there are differences between species in farming practices, it is ultimately a labour intensive crop that requires ‘green fingers’ and a high level of local ecological knowledge. As Hill describes, two cuttings of the same plant just 10 meters apart can often have very different outcomes. Industrial scale production has been tried many times and failed, largely because they rely on a hired-in labour force that aren’t equipped with local ecological knowledge and don't have the same incentives. And smallholders can potentially better adapt because of that local ecological knowledge and they have more flexibility to adapt more quickly.

Too much of a good thing

In China, areas of the Yellow Sea have experienced invasions of the green seaweed Ulva prolifera, which grows on bamboo rafts and rope nets used on seaweed farms.¹¹ Coupled with excess nutrient runoff from potent agricultural fertiliser, the consequences of overproduction can be dire, says Fred Puckle Hobbs, Former CEO of Sea Green and Founder of Singapore-based consultancy Tathva.

"Nutrient overconcentration results in overgrowth with catastrophic impacts," he said. "In addition, regulations often aren't as mature as in, say, the EU, and limited consideration is given to the risk of overproduction. Small-scale farmers want to grow more seaweeds and industrialise. But this can disturb nutrient balance and affect other marine life."

Every spring since 2007, macroalgal blooms have occurred along the Yellow sea coast. Covering an area of over 20 000 km2 annually, Ulva prolifera bloom in the Yellow Sea is one of the largest green-tide events in the world. Lianyungang City, China 2022. Photo by CFOTO via Getty Images.

Are we in danger of overproducing seaweed? In the west, probably not at the present time. Compared to Asia, the amount that is produced is small because farms have not secured markets and enabling regulations are lacking, says Chopin. Puckle Hobbs agrees that what's stopping farms from growing enormous quantities of seaweeds is the lack of established market diversity. "With the advent of novel applications and new buyers, there will hopefully be sufficient positive reasons to farm seaweeds and we would probably see positive impacts," he said. "I doubt that seaweeds will be overproduced in the near future, especially in the Europe and US, because there are too many factors that negatively influence the ability to scale."

What does the future hold?

The general consensus is that seaweed farming can be done well. Rees says that there is huge potential for it to scale up with more efficient farming methods and a better understanding of their impacts. Doumeizel, meanwhile, points to the need to avoid pesticides and better understand seaweed varieties and genetics. "We know how to cultivate 15 to 20 species out of 12,000," he said. "The west needs to learn more about different species and how to grow its own seaweeds."

He also emphasises the need in the west to increase consumer appetite for seaweeds as a food source and explain that they are good for our health and planet. Meanwhile, he says, Asia could branch out beyond food and look at other applications, such as animal feed and bio-packaging.

It's also a question of collaboration, says Puckle Hobbs. "The seaweed sector needs to be better at cross-industry collaboration and communicating various issues effectively," he said. "This requires new seaweed industry bodies, collaboration frameworks and international projects. We also need a willingness from investors to fund the right projects, more research on improved farming methods and more efficient and inclusive governance systems for seaweed farming communities, particularly in a tropical context. Processing technologies must also be reassessed and re-evaluated."

"Seaweeds are remarkable organisms," said Chopin, who has been studying them for over 40 years. "Their high biodiversity may seem surprising, but it has led to many applications based on diverse properties. Beyond the present hype causing a surge in interest for seaweeds, we need to translate this seaweed moment into a more sustainable momentum for the seaweed sector in the long term."