Here be monsters Seaweed threatens to choke ocean

Anexplosion of harmful sargassum stretches across the Atlantic. Can it be turned into a beneficial resource?

- Zan Barberton

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 have bloomed in the Atlantic Ocean. 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’ve replaced my climate change anxiety with sargassum anxiety,” said Patricia Estridge, the head of Seaweed Generation, a UK startup working to make seaweed commercially viable.

Sargassum’s appearance can be deceptive. It is beautiful, layered like golden mats on the ocean’s surface. Distinguished by bubble-like formations in its stems that keep it floating onthe surface, pelagic sargassum has sloshed about in the Atlantic since well before Christopher Columbus sailed across the Sargasso Sea: in 1492, he wrote that he feared his boat would be trapped init. 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.

What is alarming is the rate at which it is growing. Oceanographer Ajit Subramaniam first noticed it in 2018. Here was something I’d never seen before,” he said. One moment we were in the blue sea, then bam! It was all around the ship for tens, hundreds of metres.”