Thousands of tons of Rugulopteryx okamurae, an invasive seaweed species originating from Southeast Asia, are accumulating on the beaches of the Strait of Gibraltar and the southern coast of Spain, constituting what local environmentalists describe as a serious threat to regional biodiversity.

Since May 2025, local authorities in Cádiz have removed 1,200 tons of this seaweed from La Caleta, the city’s most popular beach, with a peak of 78 tons removed in a single day. « We are completely overwhelmed. It’s an environmental disaster, » explains José Carlos Teruel, head of beaches at the Cádiz city hall, adding that every time a west wind blows, a new wave of seaweed arrives.

This species, believed to have arrived via the ballast water of ships passing through the Suez Canal and discharging into the Mediterranean, has in just over ten years colonized the Strait of Gibraltar, a large part of southern Spain’s coast, the Canary Islands, the Azores, and further north, the Cantabrian Sea and the Basque Country. The seaweed was first detected ten years ago in Ceuta by a researcher from the University of Málaga.


A Devastating Economic and Ecological Impact

The seaweed has a significant negative impact on many sectors of the local economy. Tourism in Cádiz and Tarifa, a popular destination for windsurfing, is affected by the massive presence of this seaweed on the beaches, which also produces a very unpleasant odor. Fishing activities also suffer, as the seaweed traps fishermen’s nets and lines, while depleting oxygen in the seawater.

The most worrying impact concerns biodiversity. On La Caleta beach, the seaweed has displaced many native plants, and it is still unknown whether this damage is temporary or irreversible. Rugulopteryx okamurae attaches itself to rocks and other surfaces, eliminating native seaweed species. The absence of natural predators in the region, combined with its ability to reproduce both sexually and asexually and to absorb toxins, makes its eradication practically impossible, according to experts.

Juan José Vergara, a biology professor at the University of Cádiz, explains that in the early phase of such an invasion, control is possible: « It’s like detecting cancer early before it spreads. » However, the current scale makes any control impossible, and what washes up on the beaches is only a fraction of what exists underwater.


From Problem to Energy Resource

Currently, the seaweed is dumped in landfills, representing an additional cost for taxpayers. A local company that recycles seaweed to make drink containers or use it as fuel and fertilizer has requested permission to use Rugulopteryx okamurae as biomass for energy production.

However, Spanish legislation on invasive species prohibits their commercial exploitation unless they pose a threat to health and safety or facilitate their eradication—conditions that seem to apply in this case. This week, the Andalusian regional government launched a four-party plan to tackle the crisis, based on research, monitoring, and education, which includes seaweed recycling options.

Although the regional government must negotiate with the Ministry of Environment to use the seaweed as biomass, Juan José Vergara warns that even if an agreement is reached, this measure can only be part of the solution. « It’s an interesting idea, but I doubt it could eradicate or even significantly reduce the intensity of the invasion when hundreds of thousands of tons can wash up on a single beach, » he concludes.

Source : euronews

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