A fast-spreading invasive seaweed, Rugulopteryx okamurae, native to southeast Asia, is transforming the beaches of the Strait of Gibraltar and the Andalusian coast into dumping grounds for pungent, rotting algae.
The scale of the infestation has stunned locals and scientists alike. Since May, Cádiz city council has removed over 1,200 tonnes of the invader from La Caleta beach alone, including 78 tonnes in a single day — a staggering figure for a stretch of sand just 450 metres long.
“We’re completely overwhelmed. This is an environmental catastrophe,” lamented José Carlos Teruel, head of Cádiz’s beach management. “Every time the westerly wind picks up, we know the seaweed is coming back.”
The origins of the crisis can be traced to global maritime trade. Like many invasive marine species, Rugulopteryx okamurae likely arrived in European waters via the ballast tanks of cargo ships transiting the Suez Canal — flushed out into the Mediterranean, where it found a new and fertile home.
In just a decade, the alga has spread rapidly. First identified in 2010 off Ceuta, Spain’s tiny North African enclave, the seaweed has since colonised much of the southern Iberian coastline, the Canary Islands, the Azores, and even reached the cooler waters of the Cantabrian Sea and the Basque Country. Its adaptability, speed of reproduction, and lack of natural predators have made it a textbook case of unchecked biological invasion.
“It’s like cancer,” says Professor Juan José Vergara, a marine biologist at the University of Cádiz. “If you catch it early, you can contain it. But we were too slow. Now it’s out of control.”
Indeed, what washes ashore is only a fraction of the mass beneath the waves. Divers off Tarifa and Algeciras report carpets of seaweed clinging to reefs and rocky seabeds, smothering native flora and fauna. Unlike other algae, Rugulopteryx reproduces both sexually and asexually, can float freely as well as attach to surfaces, and absorbs toxins that make it unpalatable to fish or herbivores.
The consequences are already being felt. La Caleta, one of Cádiz’s most popular urban beaches, has seen visitor numbers drop as foul-smelling algae piles up on the sand. In nearby Tarifa, a global mecca for windsurfers, frustrated tourists must now wade through knee-deep tangles of seaweed before reaching the water.
The fishing industry, too, is suffering. Nets and lines become ensnared, catches plummet, and marine oxygen levels fall in algae-choked areas. “It’s affecting the entire ecosystem,” said one fisherman near Algeciras. “The sea is changing before our eyes.”
Taxpayers, meanwhile, are footing the bill. Removal and disposal of the seaweed costs local authorities hundreds of thousands of euros each season. At present, the tonnes of biomass collected are dumped in landfills — a temporary fix that raises fresh environmental questions.
There may, however, be a glimmer of hope. One local firm has proposed recycling the algae into biofuel, fertiliser or even biodegradable packaging. But Spanish law, rightly wary of commercialising invasive species, prohibits such use unless it directly supports eradication efforts or addresses a clear threat to health or safety.
“Technically, that caveat should allow us to proceed,” said Professor Vergara. “But red tape, as always, is the enemy of swift action.”
This week, the regional government in Andalucía unveiled a new four-pronged plan to confront the crisis: research, monitoring, education and, critically, exploring ways to recycle the algae responsibly. Talks with Spain’s environment ministry are under way to consider granting a special exemption for biomass use.
“It’s an interesting idea,” Vergara conceded. “But it won’t be a magic bullet. Even if we start processing some of the seaweed, we’re talking about hundreds of thousands of tonnes. That’s not something you can solve with one factory or one initiative.”
Environmentalists agree. They warn that unless coordinated action is taken — both domestically and at the EU level — the seaweed will continue to spread. Some experts suggest monitoring ballast water more strictly or implementing early detection systems in vulnerable coastal zones.
But for now, the people of Cádiz are left to cope with a crisis that no one asked for and few understand. Tourists arriving at La Caleta this summer may be greeted not by golden sands and turquoise waves, but by the sharp, sulphurous stench of decay.
“This isn’t just a nuisance,” said Teruel. “It’s a wake-up call. We need serious investment, serious science, and above all, serious urgency.”
As Spain battles one of the worst marine invasions in recent memory, one thing is clear: nature, once unbalanced, has a way of fighting back — and rarely politely. The tide may be high in southern Spain, but the solutions remain frustratingly out of reach.
Main Image: Mariajoao22 via Wikipedia
