Seaweed farming for sustainable food

Growing food on land can be challenging and costly for the planet:

• It often involves deforestation, causing habitat loss and contributing to climate change.
• Pesticides used to protect crops from pests and diseases can harm beneficial insects and ecosystems. 
• Crops need vast amounts of fresh water. 
• Intensive agricultural practices can degrade soil, leading to a reliance on artificial fertilisers that then pollute surrounding freshwater and marine ecosystems.

Climate change intensifies these agricultural challenges by altering temperature, rainfall patterns and the prevalence of pests and diseases. It also increases the occurrence of extreme weather events, further threatening food security.

One solution may lie in the ocean...

Seaweeds thrive on the simplest ingredients: sunlight and seawater, absorbing everything they need from the surrounding environment. So, seaweed farming presents an environmentally friendly, sustainable and less resource intensive alternative to farming on land.

Eating seaweed isn't new

While seaweed isn’t commonly eaten in Europe currently, it has historically been an important source of food for coastal communities. Research shows that seaweed was even a staple food for prehistoric Europeans.

Seaweed is mostly eaten in East Asia, although that’s changing. It’s used in sushi, soups, salads, as a food thickener and more.

Many seaweeds have a unique umami taste, which enhances the flavour of dishes. They’re a great substitute if you want to eat less meat and fish but don’t want to sacrifice that savoury, salty flavour.

Interest in eating seaweed is on the rise. This is important, as seaweed could provide over 100 million tonnes of extra food worldwide by 2040.

Europe accounts for only 0.8% of global seaweed production but it’s an industry that’s developing.

Expanding our diets to incorporate seaweed and reducing our intake of carbon-intensive foods such as meat could be a vital way of keeping the planet healthy.

Sustainable seaweed farming practices

While seaweed farming can have many benefits, we must be cautious not to “replicate the mistakes of land farming,” warns Professor Juliet Brodie, seaweed expert at the Natural History Museum.

Best practice in seaweed farming looks small and local. It’s about community ownership, cultivating locally sourced native species and processing and selling the product nearby to minimise carbon emissions.

Aird Fada, a Scottish seaweed farm off the coast of the Isle of Mull, is keen to embody these sustainable practices.

Aird Fada Project Officer Leigh Eisler tells us that choosing a farm’s location is key. You don’t want to pick a site that’s already full of life, as seaweed can block light from reaching the seabed, impacting the ecosystem.

Going a step further, Leigh explains that they “would like to explore the concept of ‘ocean hedges’, where some growing lines are left as a food source and more permanent habitat for creatures”. This is like how hedgerows provide habitat corridors for animals living on farmland.

But Leigh adds that such an approach can put strain on a farm’s structure. “We’d need to balance the environmental benefits with maintaining the farm’s structural integrity,” she says.

Seaweed farming has many benefits

Seaweed is a fairly low maintenance crop. “It doesn’t require any freshwater input or fertilisers,” says Leigh. “The easiest part of seaweed farming is leaving it to grow.”

Farms like Aird Fada can even enrich an area. Leigh explains, “if you ensure you are not impacting the local ecosystem, then you end up providing a floating reef”. This supports a wide variety of life.

“Seeing the whole ecosystem around the farm is really lovely,” she adds.

“Wild seaweed is settling on our lines, and the buoys and anchors act as structure for biodiversity to settle on. We’ve found them teeming with juvenile queen scallops, multiple species of crabs, crinoids [marine animals related to starfish and sea urchins] and sea squirts.”

“We’ve also observed a wide range of seabirds around the farm, which tells us that we have schools of fish darting between the lines of seaweed. I’ve even seen bottlenose dolphins and seals at the farm.”

Choosing site locations with care can have additional benefits. Leigh explains, “seaweed farms are also good to consider in areas experiencing coastal erosion, as the energy of the water is absorbed by the seaweed before it hits the coast”.

How seaweed farms are responding to climate change

Higher carbon dioxide levels in the water cause ocean acidification. While this change is affecting some calcifying species of seaweeds as levels of the minerals they need to grow decline, the impact on seaweed crops isn’t yet clear.

Malaysian seaweed researcher, Professor Lim Phaik-Eem has observed that some species are growing better in high CO₂ levels.

Seaweed can also act as a bioremediator, reducing acidification levels locally by pulling CO₂ out of the water.

Ocean warming seems to be the main challenge facing farms currently.

“The oceans are warming, and it is getting hard to grow these crops in some places,” says Juliet.

When she visited a seaweed farm in Zanzibar recently, the water temperature close to the shore was 36°C, “the limit of what the farmed seaweeds can tolerate”. Farmers are having to move their crops offshore into deeper, cooler waters, making them harder to look after.

Sometimes small marine creatures live or feed on the seaweed – this is called biofouling. It means farmers have to pull up their lines before the significant growing period, reducing their yield.

Aird Fada are seeing biofouling happening earlier in the year due to warming water temperatures.

Meanwhile, Phaik-Eem has observed through her work on Malaysian seaweed farms that warming waters are making crop diseases more prevalent and affecting seaweed growth rates.

Natural History Museum seaweed scientists have been working with local experts in both Asia and Africa to identify the early warning signs of pests and diseases there. Farmers can then act to move their crops or grow different kinds of seaweed.

Potential of seaweed farming beyond food

Seaweed’s versatility extends far beyond the dinner plate. It can also be used as:

• livestock feed, remarkably reducing methane emissions from cattle
• natural fertiliser, decreasing our reliance on polluting artificial fertilisers
• a sustainable material, being made into a biodegradable alternative to plastic

Furthermore, seaweed farms can boost the economy of coastal communities, creating jobs.

Leigh also has a vision of seaweed farms being used to recycle nutrients in agriculture.

Growing seaweed in areas of water near agricultural farms where there is artificial fertiliser run-off, along with farming filter feeders like oysters, could help reduce the nutrient overload, cleaning the water and helping to restore ecosystems.

In turn, the seaweed could be used to fertilise the farm, reducing the use of artificial fertilisers.

Time to try a taste?

Seaweed is a promising and sustainable solution to our ever-growing food challenges and could become a future staple in your diet.

So why not try eating seaweed if you haven’t given it a go yet – it could hold the key to a healthier planet.