Thousands of tonnes of an aggressive invasive seaweed from East Asia are washing up on beaches along the Strait of Gibraltar and Spain’s southern coast, posing a major threat to the region’s biodiversity, local environmentalists warn.

Since May, Cádiz city council has removed 1,200 tonnes of Rugulopteryx okamurae from La Caleta, its most popular beach – including 78 tonnes in a single day.

“We’re completely overwhelmed. This is an environmental catastrophe,” said José Carlos Teruel, responsible for Cádiz city council’s beaches. “Whenever the wind is westerly, we know we’re in for another wave of seaweed.”

Like many invasive marine species, the alga is thought to have arrived in ballast water discharged by ships passing through the Suez Canal into the Mediterranean.

In just over a decade, it has spread across the Strait of Gibraltar, much of southern Spain, the Canary Islands, the Azores, and as far north as the Cantabrian Sea and the Basque Country.

“It was first spotted 10 years ago in Ceuta, Spain’s north African enclave, by a researcher from Málaga university, but the authorities are always too slow to react,” said Juan José Vergara, a professor of biology at the University of Cádiz.

“In the first phase of an invasion such as this it can be controlled. It’s like catching cancer early on before it spreads,” Vergara said, adding that what washes ashore is a fraction of what is underwater.

“But now the scale of it makes it impossible to control. In other seaweed invasions we’ve seen things revert to normal after a period of 10-15 years but many scientists say they’ve never seen an invasion on this scale.”

The seaweed is hitting the local economy on several fronts: damaging tourism in Cádiz and nearby Tarifa – a hotspot for windsurfing – disrupting fishing by clogging nets and lines, and depleting oxygen in the water. The cost of removing and disposing of it also falls to taxpayers.

The greatest concern, however, is its impact on biodiversity. At La Caleta, the seaweed has displaced many native plants, though it is unclear whether the damage is reversible.

The species attaches to rocks and other surfaces but can also drift freely, outcompeting native seaweeds. With no natural predators in the region, the ability to reproduce both sexually and asexually, and a tolerance for toxins, experts say it is virtually impossible to eradicate.

Currently, the collected seaweed is sent to landfill. A local business that recycles seaweed into drinks containers, fuel, and fertiliser has sought permission to use Rugulopteryx okamurae as biomass for energy production.

However, Spanish law on invasive species bans commercial use unless it helps protect public health or supports eradication efforts – an exemption that appears to apply in this case.

This week, the Andalusian government unveiled a four-part plan to tackle the problem, focusing on research, monitoring, and education, and exploring recycling options for the seaweed.

To proceed with biomass production, the regional authority will need approval from Spain’s environment ministry. Even then, officials say it would only form part of the solution.

“It’s an interesting idea but I doubt it will be able to eradicate or even significantly diminish the intensity of the invasion when hundreds of thousands of tonnes can wash up on a single beach,” he said.

 

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