"It’s the first time I’ve seen this in 60 years," says 79-year-old Noël Tanguy, seated in the wheelhouse of his boat as his two sons unload a cargo of brown seaweed at the port of Lanildut, in Brittany’s Finistère department.

The patriarch of what he describes as the region’s oldest family of seaweed harvesters — "from father to son since 1850" — blames the "catastrophic" season on global warming. Wearing a wide-brimmed beige hat, he fears the profession may not survive much longer. "It’s alarming. I don’t think this profession has more than a year or two left. Harvest volumes have collapsed this year, and boats are returning with only half their usual loads," he says.

Between May and September, the dozen or so seaweed harvesting vessels operating from Lanildut — Europe’s leading seaweed port — typically harvest between 40,000 and 55,000 tonnes of Laminaria digitata, a long, strap-like brown seaweed.

This rock-anchored seaweed, known locally as tali by Breton harvesters, is pulled from the seabed using a “scoubidou” — a hook attached to a hydraulic arm. On this sweltering July afternoon, the vessels take turns unloading their dripping cargo, which is immediately loaded into dump trucks by a mechanical excavator.

"Warming and overexploitation"

Everyone agrees this year’s harvest has been disastrous, describing it as "useless" or simply "crap," depending on who you ask. "We’ve been seeing yields decline for the past three or four years, but this season is by far the worst. I’ve never experienced anything like it," says 58-year-old Patrice Hamon, owner of the Archange. "The outlook is bleak. I’m not sure there will still be any seaweed harvesters in ten years," adds fellow harvester David Tanguy, 49.

Harvesters say their traditional harvesting grounds are shrinking, while bulbous kelp (Saccorhiza polyschides), known locally as toser, is increasingly displacing Laminaria digitata, or tali. "The water is warmer, so this invasive seaweed grows much faster. It’s like weeds taking over a lawn," explains 40-year-old Julien Tanguy. "In around 70% of the areas we harvest, the seaweed is no longer the right species—it’s this parasitic one instead." He attributes the decline to a combination of climate change and decades of intensive harvesting. "We’ve been harvesting too much for more than 15 years, and that certainly hasn’t helped."

His observations are consistent with recent ocean temperature data. On Friday, sea surface temperatures off the coast of Brittany hovered around 20°C — more than 3°C above the seasonal average, according to the European Copernicus climate service. By contrast, Laminaria digitata thrives in much cooler waters, typically between 10°C and 15°C.

Jobs and ecosystem at risk

"Temperatures are rising very, very quickly," observes Yvon Troadec, a retired harvester and coordinator of the seaweed working group at Brittany’s regional fisheries committee. "We knew this trend was underway, but we never expected it to accelerate so quickly. We thought it would take another 20 years to reach these temperatures."

In a study published in 2013 in the journal PLOS One, researchers projected that Laminaria digitata could disappear locally from parts of the French, English and Danish coastlines as early as the first half of the 21st century as a result of global warming.

The loss of these kelp forests would affect entire ecosystems as their dense underwater canopies provide habitat and shelter for numerous species of fish and crustaceans, making them a cornerstone of coastal marine ecosystems. Their disappearance would also threaten the livelihoods of around 30 seaweed harvesters and the 160 employees working at Finistère’s two seaweed processing plants.

"It’s a major concern for me... but I want to remain optimistic," says Arnaud Delafon, manager of the JRS Marine Products plant in Landerneau. The company extracts alginate — a natural gelling and thickening agent derived from brown seaweed — for use in the food, cosmetics and pharmaceutical industries.

With local harvests falling far short of demand, the company has been forced to import far more expensive dried seaweed from Chile and Peru. "Our goal is to rely on a local resource," Delafon says. "These seaweed beds are our primary raw material. It is in everyone’s interest to preserve them."