Why does this matter?

Seaweed forms an important part of human diets and medicine and has been cultivated in different parts of the world for centuries. In recent decades, the market has seen rapid growth due to increased demand from other sectors. Today, different types of brown, red and green alga are used in a wide range of products, including food, biofuels, textiles, pharmaceuticals, cosmetics, industrial gels and bioplastics. In 2019, more than 35 million tonnes of seaweed were produced globally.

Cultivation is well-established in Asia, which accounts for 97% of the world’s harvest. More than half of the global seaweed comes from China, while Indonesia, South Korea and the Philippines are also major producers. In August 2022, the European industry received a boost when Netherlands-based group North Sea Farmers completed the world’s first mechanical harvest at an offshore seaweed farm. By 2028, the global market could be worth about $25bn, up from $15bn in 2021.

A new study, led by researchers from the University of Queensland, looked at 34 commercially important seaweed species and mapped suitable locations for large-scale farming within countries’ exclusive economic zones (EEZs). It found that 650 million ha of ocean could support seaweed production. Indonesia and Australia have the greatest potential for cultivation, containing 114 and 75 million ha of suitable ocean within their EEZs, respectively. Australia has a particularly high diversity of native seaweed species, many of which have not yet been considered for commercial use, the authors noted.

Further, the scientists analysed how rapid scaling of seaweed farming could help mitigate other environmental problems – including pollution and emissions from land-based food production – using the Global Biosphere Management Model (GLOBIOM). They found that raising the share of human diets based on seaweed to 10% (up from 2% in parts of Asia today) could free up 110 million ha of land currently used for agriculture, an area twice the size of France. Thus, seaweed farming could play an important role in reducing land-use pressures, one of the main drivers of climate change and global biodiversity loss. Seaweed consumption is also known to offer health and nutritional benefits due to its high contents of dietary fibre, fatty acids, essential amino acids and vitamins A, B, C, and E.

Unlike land-based farming, seaweed production doesn’t need any freshwater, pesticide or fertiliser input, making it a more sustainable way to produce food. Moreover, seaweed sequesters CO2 and absorbs nitrogen and phosphorus from surrounding waters. This could help tackle ocean acidification and harmful algal bloom in regions with high levels of water pollution. Recently, Norway launched the world’s first salmon and kelp farm that could become a role model for more environmentally-friendly aquaculture. The site is based on a circular concept in which the kelp is fully integrated into salmon farming, recycling nutrients released by the fish and providing alternative feed materials.

Expanding seaweed production would also help combat greenhouse gas emissions from conventional agriculture, the researchers said. Cultivating a red algae species called Asparagopsis for cattle feed supplements could prevent up to 2.6 billion mt of CO2-equivalent per year by 2050. Various companies, including Blue Ocean Barns from the US, Sweden’s Volta Greentech and Australia’s FutureFeed, have started selling seaweed-based supplements, which are estimated to cut enteric emissions from cattle by over 80%.

Nevertheless, the study authors acknowledge that massive scaling of the seaweed industry could have its own negative environmental and social impacts that would need to be carefully managed.

A 2019 study outlined the main environmental issues arising from large-scale seaweed farming. One problem is the increased competition for light among marine species. One kelp production site in China, for example, has been shown to suppress phytoplankton abundance during the growing season, which can have ripple effects throughout the food chain. Moreover, cultivated seaweed forests lead to increased surface drag, thereby hampering the natural water flow, which is vital for the exchange of nutrients between neighbouring habitats. The potential risks to marine ecosystems require careful consideration of project locations, especially near enclosed water bodies, the scientists warned.

The application of synthetic polymer ropes on seaweed farms is another major risk factor. Most farms use grid systems based on vertical or horizontal rope raft culture, which can cause the entanglement of marine species, while discarded or lost components add to the problem of marine plastic pollution. Other risks from large-scale seaweed farming include nutrient depletion in regions without nitrogen pollution, increased noise and habitat destruction, and negative impacts from the introduction of non-native species, diseases and parasites to coastal ecosystems.

In order to minimise environmental risks and enable informed decision-making, the researchers highlight the need for more targeted research and monitoring in cultivating countries. More specifically, they state that an understanding of location-specific baseline conditions – including local biodiversity, nutrient flows and disease prevalence – is a prerequisite for sustainable seaweed farming.