LATE last spring, in a sleepy coastal town in Northern Ireland, a fishing boat returned to shore overflowing with seaweed. Back when Portaferry was a thriving fishing village, that catch would have been an embarrassment. For and her team, though, the slimy brown boatload was cause for celebration.
A year on from their successful first harvest, Mooney is heading out for a tour of the underwater farm after several weeks of stormy weather kept her away. In a sheltered inlet, row after row of ropes float near the surface. Several months ago, each rope was seeded by hand with spores cloned in a hatchery. Now, thick with blades of kelp up to 4 metres long, they are almost ready to be gathered in again.
It’s hard work, and slow. “Seaweed cultivation is still in its infancy,” says Mooney, a marine biologist at Queen’s University Belfast, UK. “We’re way back with handheld ploughs.” But despite using old-fashioned techniques, Mooney is at the crest of an aquacultural revolution spurred on by seaweed’s many talents. Whether as food, drug or biofuel, seaweed is incredibly versatile. So versatile, in fact, that some think seaweed could grease the wheels of an even bigger revolution: the industrialisation of the sea.
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Seaweed cultivation isn’t new. In East Asia, a $5 billion crop is harvested every year, mostly for food. But other than nori, edible seaweed in the Porphyra genus also known as laver – which can sell for around $15 a kilogram – most uses of seaweeds have been low value. They are an energy-boosting additive for animal feed. Extracts are also widely used as natural fertilisers and as thickening agents in products ranging from toothpaste to paint.
But seaweed has far more valuable uses. Certain species contain unique substances that could have important medical applications. Some show promise in fighting diseases such as cancer and diabetes, for example. Meanwhile, the construction industry is investigating its use as building insulation. It could also be an abundant source of biofuel. An area of about 2500 square kilometres – roughly the size of Luxembourg – could grow enough seaweed to produce 2 billion litres of bioethanol, according to , an independent research organisation in Norway. That’s half the European Union’s current ethanol demand.
“Seaweeds contain unique substances that could have life-saving applications”
The trouble is, little is known about how to grow seaweed successfully on an industrial scale. In China, for example, fields are tended by hand using age-old methods, which is only possible because of the availability of cheap manual labour. With her trial farm, part of a major project funded by the European Union called , Mooney is effectively starting from scratch.
Seaweeds are large red, green or brown algae that live naturally on or near the sea floor but can grow almost anywhere. Like any plant, their growth varies depending on the environment. What works in the North Sea, for example, might not in the Adriatic. Each species has a unique life cycle and sensitivity to temperature, nutrients and light (see diagram). Today about 20 species are farmed around the world, from cold-loving kelps like Mooney’s Laminaria to tropical red species such as Kappaphycus, which is used as a thickener. “We want to come up with growth models that you can tweak to optimise cultivation at different sites,” says Mooney.
Pests are one poorly understood issue. Bottom-grazing fish nibble the tips off seaweed if farmed in shallow water. Seaweeds also provide convenient growing surfaces for fungi, and other algae. When Mooney lifts a rope out of the water, she sometimes finds strips of kelp colonised by sludge-like algae. In warm weather, algae and fungi can form a thick layer on the blades and block sunlight. “A month or so after harvest time in June it can get disgusting,” says Mooney. Her team is not yet sure exactly which organisms are to blame.
Disease is a major problem on seaweed farms in China, where large fields are often filled with plants of a single strain. “Like with land plants, the process allows you to select more easily for certain characteristics to boost growth,” says of the Scottish Association for Marine Science in Oban, UK. “But a monoculture is far more susceptible to disease.” Bacterial infections like ice-ice, which turns seaweeds such as Kappaphycus white and hard, are rampant. As much as half of a farm’s crop can be ruined.
Chinese seaweed farmers deal with the problem by continually crossing wild strains back into their stock and manually removing diseased individuals. But the longer-term effects of seaweed farming are little known, and need to be investigated if larger-scale cultivation is to take root. Some farmed plants will always float away and interact with wild populations, so Mooney wants to make sure cultivated seaweed won’t weaken wild populations through breeding with them. If we start tapping into the sea, we need to be sympathetic, she says. “You don’t want to make the same mistakes made on land.”
Done the right way, though, large-scale seaweed cultivation could be good for the environment. For example, it can help mitigate the environmental impact of fish and seafood farms, using up the carbon dioxide they produce and feeding off the nitrogen in the animals’ faeces. In China, where seaweed is beginning to be used for this purpose, it has reduced the in some cases.
On another pilot site off the south coast of Ireland, researchers are experimenting with this type of “multi-trophic” aquaculture as part of a European project called . Julie Maguire from the Daithi O’Murchu Marine Research Station in Bantry is finding that local seaweeds thrive when grown around a salmon farm, soaking up the nutrients it produces. Adding bottom-dwelling sea cucumbers, which are being investigated as a source of food for humans, seems to give the seaweed an even bigger boost. “It grows fantastically well,” says Maguire. “We’ve been getting 20 kilograms whereas other producers in Ireland only get 10 kilos at best in the same amount of space.”
That seaweed does well in combination with other aquaculture is important. Large-scale cultivation will need to be done offshore, not in coastal areas. And teaming up could be the key. “There is unbelievable competition for getting space at sea,” says Maguire. “It’s a misconception that there is unlimited space up for grabs.” Food and energy producers are claiming prime offshore real estate and the world’s oceans are expected to see massive development in the next 10 years. In Europe, for example, the is considering multi-use offshore sites in the Baltic, the North Sea, the Atlantic and parts of the Mediterranean. Seaweed is part of that vision, an integral part of a new approach to exploiting the sea.
Offshore development requires significant investment. Transportation will be costly and many processes will need to be controlled remotely or automated. Some argue that energy companies setting up wind farms or wave energy devices could cut costs by renting out infrastructure to aquaculture businesses. So researchers are now ditching ropes and looking at other methods for offshore cultivation (see “Old rope, new tricks“). “It would be great to have the offshore equivalent of a business park somewhere off in the Atlantic, with fish farms, seaweed fields and a wind farm all in one place,” says Maguire. “It makes sense so that everyone can share resources and equipment.”
Growing seaweed around artificial structures like wind farms also reduces their impact on local ecosystems. “The area below a seaweed farm could act as a safe harbour for fish, helping to maintain or increase the population of certain species,” says Carlo Hamelinck from Ecofys, a renewable energy consultancy looking at ways to integrate offshore wind farms with seaweed production.
Clean-up crop
Of course the success of all these enterprises is tied to the future state of the oceans. In some parts of the world, rising sea temperature and acidification are already grave concerns. Off the coast of the Tanzanian island of Zanzibar, for example, many farmers have . “It’s one of the biggest issues farmers will have to tackle if it expands on a larger scale,” says Narriman Jiddawi, a marine ecologist from the University of Dar es Salaam in Tanzania.
Seaweed doesn’t necessarily need to be grown at sea, at least for smaller scale uses (see “Land ahoy“). But equally, it could be part of solving some of our problems. Seaweeds can act like sponges, soaking up pollutants. Certain types will grow in sewage water or waste streams from industrial fermentation systems, high in carbon dioxide and nitrogen. So they could be used to clean up the water.
Researchers in Japan are even looking at using seaweed . Extracting even half of this uranium, they say, could provide 6500 years’ worth of nuclear energy, without the environmental damage of uranium mining.
“Seaweed might soak up naturally occurring uranium for nuclear energy”
“Imagine prairies of floating seaweed masses, to be harvested or not, providing services like bioremediation, carbon dioxide fixation and enriching the biodiversity of an area for fisheries,” says Ricardo Radulovich from the University of Costa Rica in San José, who is investigating growing seaweed in the quiet waters of the Caribbean gyre.
Back in Portaferry, Mooney sees seaweed farming as a way of getting local fishing communities back on their feet. The people are already adept with boats and ropes, so it would just be a matter of modifying their skills. At the same time, there is a growing demand for seaweed as food in the area, as chefs seek out organic, locally grown sources. “Seaweed cultivation is going to be a big thing,” says Mooney. “There is so much good stuff you can do with it.”
Read more: “Seaweed supper: recipes for a three-course meal”
Land ahoy
Not everyone is sold on the sea. at the University of Wollongong in Australia is looking at seaweed cultivation for medical applications. And for that, she prefers growing it on land.
Unlike seaweed grown for biofuel or food, medical uses need highly controlled growing conditions. Using 25-metre-long saltwater tanks, Winberg can manipulate the plants to encourage the traits she needs.
Seaweed cells are held together by different kinds of “gel”, which give structure to the blades. Some of the more starchy gels are already used as thickening agents in foods and cosmetics. Now others that appear to have immune functions are in the spotlight. They evolved to protect seaweed from an ocean’s worth of bacteria, fungi and viruses. Still others are used for cell-to-cell communication. “We are only just learning that each species has unique gels, each with its own molecular fingerprint,” says Winberg.
Some of these gels have an effect on cells in other plants and animals, in some cases triggering pathways that protect from disease. Certain gels could help manage diabetes, for example, by influencing enzymes involved in controlling blood sugar levels.
Others are being investigated for their anti-inflammatory properties and for possible use in cancer drugs and antibiotics. Winberg is using the adhesive properties of one gel in a biomaterial that can be . Some gel components have even been shown to affect human stem cells, controlling whether they differentiate into bone or muscle tissue.
Many seaweed species have yet to be classified, so there are likely to be many more gels with valuable medical uses. Seaweed may end up being grown in artificial lakes on land as well as in the sea.
Old rope, new tricks
If seaweed is to be cultivated on an industrial scale, we are going to need new strategies for growing it. For example, farms out to sea will have to be more robust than the traditional but vulnerable rope systems used in shallow coastal waters.
from the Alfred Wegener Institute in Bremerhaven, Germany, and his colleagues have developed a floating ring with a compact structure that allows it to withstand high waves and strong currents. The device can also be hoisted out of the water with seaweed attached, making it easier to harvest.
Meanwhile, Philip Kerrison of the Scottish Association for Marine Science in Oban and his colleagues are looking to maximise productivity. They are developing giant underwater “blankets” on which to grow seaweed. Using a sheet of material instead of parallel ropes provides a much larger surface area for cultivation.
Kerrison hopes that such systems will also pave the way for mechanised harvesting. “Ideally, a marine combine harvester would come and strip seaweed off, either above or below the water,” he says.
Similar material could be used to create storage bags for harvested seaweed, Kerrison says. Seaweed degrades quickly when it is ripe, so large quantities need to be harvested in a short time. Storing it near the growing site would save space on land. If the crop is for biofuel, the fermentation process could be started at sea (see diagram).
This article appeared in print under the headline “Kelp wanted!”
