Seaweed has been having a moment. Eco-influencers and columnists rave about its benefits, in everything from beauty products to biofuels. Jamie Oliver has embraced it as a recipe ingredient; Victoria Beckham uses it to keep off the pounds. And they’re right: seaweed is packed with nutrition, it sucks up carbon and is an amazingly versatile addition to the green economy.
But one type of seaweed is not a benign force. Vast fields of sargassum, a brown seaweed, have bloomed in the Atlantic Ocean. Fed by human activity such as intensive soya farming in the Congo, the Amazon and the Mississippi, which dumps nitrogen and phosphorus into the ocean, the sargassum explosion is by far the biggest seaweed bloom on the planet. The Great Atlantic Sargassum Belt, as it’s known, is visible from space, stretching like a sea monster across the ocean, with its nose in the Gulf of Mexico and its tail in the mouth of the Congo.
“I think I’ve replaced my climate change anxiety with sargassum anxiety,” says Patricia Estridge, CEO of Seaweed Generation, a UK startup working to make seaweed commercially viable.
Sargassum’s appearance can be deceiving. It is beautiful, layered like golden mats on the surface of the open ocean. Distinguished by bubble-like formations in its stems that keep it floating on the surface, pelagic sargassum has sloshed about in the Atlantic since well before Christopher Columbus sailed across the wide Sargasso Sea: in 1492, he wrote that he feared his boat would be trapped in it. But even early witnesses recognised its value: it provides a safe harbour and breeding ground for fish, turtles and other marine life. Under the surface it teems with life, like an upside-down reef.
What is alarming, is the rate at which it is growing. Oceanographer Ajit Subramaniam, who has run scientific research expeditions in the South Atlantic for 25 years, first noticed it in 2018. “Here was something I’d never seen before,” he says. “One moment we were in the blue sea, then bam! It was all around the ship for tens, hundreds of metres.”
Unwilling to believe his eyes, he talked to other oceanographers, who confirmed that there was a huge sargassum bloom in the South Atlantic. Chuanmin Hu and his team from the University of South Florida’s (USF) optical oceanography laboratory had been monitoring it using satellite imagery since 2011 and had seen it explode in size. In June 2022, Hu estimated the size of the Great Atlantic Sargassum Belt to be 24.2m tonnes – about four times the weight of the Great Pyramid of Giza. [Continue reading…]