The world's fastest-growing source of food

The green fronds that grow along much of India's shoreline have large potential as a sustainable food source, while helping to fight climate change.E

Emerald-green waters and bobbing catamarans welcome one on the way to Pamban Island, also known as Rameshwaram, a sacred pilgrimage site in the state of Tamil Nadu. But just below the sea’s surface, there is a change taking place which could transform the region's ecosystem, economy and even its cuisine – these coastal villages are the home of India's seaweed boom.

Although seaweed has been used in Indian folk medicine for thousands of years, it has never played as large a part in Indian culture as it has in other Asian countries. However, picking seaweed for traditional remedies is an age-old practice along coastal settlements such as Pamban Island and the Gulf of Mannar, a richly biodiverse area.

Here, locals have historically collected natural wild seaweeds indigenous to the region. It is to these villages that India is turning to as a model for seaweed cultivation, which globally has become the fastest-growing sector of food production, increasing by 8% every year.

The tropical waters of southern India form an ideal environment for seaweed to thrive (Credit: Alamy)

Researchers in India have long been proposing seaweed cultivation as a form of sustainable agriculture. Much of India's coast is ideal for seaweed cultivation with suitable tropical weather, shallow waters and a rich supply of nutrients. The regions of Gujarat and Tamil Nadu harbour the highest seaweed biodiversity in the country, with around 282 species being reported along Tamil Nadu's 1,000km (621 miles) coastline alone. In total, as many as 841 species of seaweed thrive along the Indian coast, though only a few are cultivated.

The benefits could be significant. India's economy is an agrarian one, with 60% of its land used for agriculture. But close to 47% of the country's cultivable land is being lost to soil degradation. Water erosion is responsible for more than a third of this loss – but, through seaweed, water could also be part of the solution.

"[Seaweed has] an innate ability to combat malnutrition being a perfect source of iodine, vitamins, and proteins," says Dinabandhu Sahoo, a botanist at Delhi University who has argued for the need for a "blue revolution" in Indian agriculture. That revolution could be getting closer, with India's government announcing this summer some $87m (£65m) in subsidies for seaweed farming initiatives over the next five years.

Seaweed's nutritional value is far from its only appeal as a crop. Seaweed gains its energy through photosynthesis, in a similar way to plants (though seaweeds are actually macroalgae). Seaweed absorbs carbon dioxide, converting the carbon to sugars for energy, and releases oxygen into the water.

Previously, it was believed that much of the carbon stored in seaweed would eventually be released again when the algae decomposed in the ocean. But the discovery of large quantities of dead seaweed deep in ocean-floor sediments has shown that when seaweed dies, much of it is swept out to the ocean, eventually sinking to the seafloor where its carbon is locked-up in sediments. As a result, seaweed cultivation has been identified as a carbon sink that could help mitigate climate change, according to research by seaweed ecologist Dorte Krause-Jensen and colleagues at Aarhus University, Denmark. And apart from storing carbon, seaweed forms one base of the marine food web, along with phytoplankton, and provides food and a habitat for a number of marine animals.

Seaweed harvesting has become an important source of income to coastal communities, in particular for women (Credit: Alamy)

But for all its attraction, the uptake of seaweed cultivation in India got off to a slow start. Some of the first efforts were in 1987, when the species Kappaphycus alvarezii, native to the Philippines, was acquired by the Central Salt and Marine Chemicals Research Institute (CSMCRI), a laboratory part of India's Council of Scientific and Industrial Research.

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The intention was to meet the increasing demand for seaweed used in the industrial manufacture of agar – a jelly with many uses, including in food, cosmetics and in laboratories for growing microorganisms. After a decade of lab and field trials at Port Okha in Gujarat, the seaweed was introduced at Mandapam, Tamil Nadu, in 1997 with just 5g of seed material, says Eswaran K, a scientist at the CSMCRI's Marine Algal Research Station, who has spent the past 27 years in Mandapam studying seaweed.

This 5g of seed material propagated over the years and has resulted in the successful seaweed cultivation farms along a 100km (62-mile) coastline near Palk Bay.

Seaweed has been identified as an important carbon sink, so large-scale cultivation could help absorb the impacts of climate change (Credit: Alamy)

But large-scale seaweed harvesting only began in earnest around the year 2000, when CSMCRI licensed the technology to PepsiCo, who were interested in using seaweed not as a food crop but to produce carrageenan, a compound used in food, cosmetics and industry. "This heralded commercial seaweed cultivation in India," says Eswaran.

PepsiCo sold its seaweed fields in 2008, which were then eventually bought by AquAgri, one of the first Indian firms to venture into commercial seaweed cultivation. The firm now has 18 seaweed cultivation sites in Tamil Nadu, providing jobs to 650 fisherfolk, predominantly women.

Muthulakshmi Namburajan has been harvesting and cultivating seaweed for a total of 38 years. While she used to spend more time in deeper water collecting seaweed, she now avoids the rougher waves as the work is physically demanding. "I prefer being close to the shores spending my time catering to the rafts," she says. From these bamboo rafts, where seaweed grows along ropes anchored by stones, Namburajan harvests, dries and cleans up to 50kg (110lb) of seaweed a day.

The surge in seaweed cultivation has had a positive socio-economic impact on the coastal communities in India, particularly among women seaweed farmers, helping them increase their economic independence.

One seaweed raft can yield up to 200kg seaweed in around 45 days (Credit: Alamy)

In total, there are 1,200 families involved in seaweed cultivation along the coasts of Tamil Nadu, Eswaran says. Each provided with 45 bamboo rafts to cultivate and harvest, one per day. Each raft typically yields 200kg (440lb), of which 50kg (110lb) is used to start cultivating the next raft.

And seaweed cultivation is set to grow further in India, with CSMCRI working with the Ministry of Fisheries to begin seaweed cultivation of both native and exotic species of seaweed along a 100km (62-mile) stretch of shoreline. The seaweed is not only destined to be a food source, but also a source of biofuels, bio-fertilisers and other products. While the CSMCRI's seaweed biofuel is still being perfected to make it economically and environmentally viable, its liquid bio-fertiliser has been shown to boost crop yields and has been rolled out to market.

Yet seaweed cultivation may come with its own ecological downsides. Unchecked wild growth of seaweed has been shown to damage coral reefs in the Caribbean, while some coral-dwelling fish appear to prefer corals unfettered by seaweed.

In India's Gulf of Mannar, concerns have been raised that the coral reefs around the island of Kurusadai were suffering from a seaweed invasion that had drifted in from nearby cultivations, though a study by the CSMCRI suggested that only a small area of 77 sq m (828 sq ft) had been affected. Eswaran notes that use of suction pumps to pick up any stray fronds of seaweed can help minimise the risk of cultivated seaweed establishing amid coral reefs.

With the Indian government announcing plans to ramp up seaweed cultivation, it could provide a stable source of income to coastal villages (Credit: Alamy)

According to the United Nations' Food and Agriculture Organization's latest report on the seaweed trade, the fast-growing global seaweed market is already more than $6bn (£4.5bn) a year. India's present seaweed value is estimated to be around $500m (£370m), despite a bumpy ride in recent years. "In 2013, close to 1,500 metric tonnes of seaweed was harvested," says Abhiram Seth, founder of AquAgri. "But then, El Nino and global warming contributed to increasing the temperature of oceans. That's resulted in lower yield in the years to come."

There is also a dearth of quality seed material after mass mortality in 2013-14 due to high sea temperatures, adds Eswaran. This damaged the reproduction capability and vigour of Kappaphycus alvarezii species. "To overcome this, we are working towards developing a heat-resistant strain and establishing a functional seed bank," says Eswaran, though this research is still in its early stages.

For a food historically much neglected in Indian cuisine, seaweed is set to have a remarkable influence on the nation's coasts. And as this algae can help lock up carbon and save agricultural land, perhaps it deserves a more prominent place on the nation's plates.

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