How seaweeds can be a sustainable source of food and other materials
‘Large seaweeds are essentially like underwater trees. They are the foundation of shallow reefs and they dominate a quarter of the world’s coastlines,’ says professor Adriana Vergés, a marine ecologist at the University of New South Wales in Australia. ‘They provide food, habitat and shelter for thousands of marine species, and are one of the most productive ecosystems on the planet.’
Humans have also depended on seaweeds for millennia, resourcefully farming them for food, medicines and building materials since they were first consumed in Japan at least 1,500 years ago. After the agricultural revolution of the 17th century, many countries dropped seaweeds from the menu, while others, especially across Asia, continued their love affair with the algae. Indonesia, the Philippines and China now lead the production of farmed seaweeds, and more than 30 million tons are harvested each year, a figure that has at least doubled in the last decade. As the human population grows, increasing the pressure on agricultural land, fresh water and wild terrestrial spaces, some are heralding seaweed as a potential solution to combat global hunger.
‘We should all eat more seaweed. It’s an incredibly nutritious source of fibre, vitamins and minerals and it’s also a very sustainable food to produce,’ says Adriana.
Cook and author of The Urban Forager: Find and Cook Wild Food in the City, Wross Lawrence, agrees: ‘I believe seaweed will play a major role in our future on this planet. My farm produces seaweed that can be used as a biofuel, medicine, fertiliser, compostable packaging and cattle feed, as well as a foodstuff for human consumption.’
Fresh or dried seaweeds are a popular form of animal fodder and have the added advantage that animals fed on them produce fewer greenhouse-gas emissions, while harvesting natural polymers from seaweeds could help to reduce human reliance on harmful petrochemicals and synthetic fibres.
‘There are many health benefits that come from adding seaweed to your diet’, says Wross. ‘The more research is carried out on seaweeds, the more incredible they prove themselves to be. Seaweed is the future and we need to be talking more about it.’
How seaweed can play a key role in the fight against climate change
Marine environments have absorbed around one-third of human carbon emissions since the start of the Industrial Revolution, with the carbon that’s captured and stored by these ecosystems known as ‘blue carbon’. ‘Seaweeds capture huge amounts of carbon and some scientists estimate that about 10 per cent of this is sequestered when bits of seaweed break off and end up in the deep sea,’ says Adriana. ‘The largest seaweed of all, giant kelp, creates large underwater forests, supporting biodiverse ecosystems and is one of the most productive seaweeds on the planet.’
According to a 2021 BBC report, seaweeds (including kelp) are believed to sequester nearly 200 million tons of carbon dioxide every year – as much as New York State’s annual emissions. This makes protecting the seaweeds we have – and restoring those that we’ve lost – incredibly important.
Why are underwater forests in decline and what can be done about it?
Adriana leads a research group that focuses on the ecological impacts of climate change and the conservation of the world’s algal forests and seagrass meadows, which are increasingly under threat. She’s also the founder and chief investigator of Operation Crayweed, a restoration project that’s re-establishing Australia’s lost underwater forests.
‘Pollution and climate change are two of the main human causes of decline of seaweed forests,’ she says. ‘In northern California, 95 per cent of the bull kelp has disappeared, Tasmania has lost 95 per cent of its giant kelp forests, and in Sydney, sewage pollution has ravaged the crayweed forests across the entire metropolitan coastline. Many brown seaweed species, including kelp, need cold, nutrient-rich waters to thrive, which makes them especially vulnerable to climate change. An extreme heatwave in Western Australia caused the disappearance of golden kelp across 150km of coastline, reducing the distribution range of the species.’
Bottom-dredging and coastal development have also greatly impacted seaweeds, while agricultural run-off has seen a dramatic rise in naturally occurring algal blooms, which can throw ecosystems drastically out of balance. The tides of Sargassum seaweed that have been sweeping ashore in the Caribbean suffocate life in the sea and affect the tourism which relies on the islands’ pristine white sands.
Overfishing of marine predators has also contributed to the decline of all seaweed groups because it can lead to blooms of sea urchins, which act like underwater bulldozers, overgrazing seaweeds and leaving barren reefs behind.
The Kelp Forest Alliance is encouraging governments, organisations and individuals to come together to protect and restore 30 per cent of the world’s kelp forests by 2040. So far, different organisations around the world have restored 14,000 hectares, but that leaves a further million, while three million hectares must be protected in order to meet the challenge.
From sunlight-dappled forests of golden kelp to vibrant iridescent green strands and delicate feathery red fans, each of the ocean’s precious seaweeds supports an abundance of life, even if we can’t always see it.
‘Worldwide, seaweeds are the foundations on which seashores are built, and without them our beaches, cliffs and wetlands would be little more than sandy deserts,’ says John Bothwell. ‘When you stand on a beach and look out over the sea, all you see is the water in front of you and the rich flora on the land behind you. But if we were to drain the oceans, there would be as much growing on the seabed as there is on the land: seaweeds are constantly there, working away. They’re a massively important part of life on Earth, and one that we all need to appreciate more.’
Read more about Adriana’s work at operationcrayweed.com.
To get involved in kelp forest restoration, visit kelpforestalliance. com. Follow Wross on Instagram @wrosstheforager. Seaweeds of the World: A Guide to Every Order, by John H Bothwell, is published by Princeton Press.
You can read more articles about conservation, the environment and sea life in the latest issue of Swim magazine.