Summer has once again turned Andalusian beaches green, but not with native vegetation, rather with the massive presence of Rugulopteryx okamurae , the Asian seaweed that has been steadily spreading along the coastline since 2015. What began as an isolated incident in the Strait of Gibraltar has become a structural problem that scientists now consider unstoppable.
The scientific community has been unequivocal: eradicating this invasive species is technologically and biologically impossible. Efforts are now focused on mitigating its effects on biodiversity, fishing, and tourism, while local councils incur costs of millions of euros to remove tons of biomass every day.
An unstoppable invasion
The Marine Biology Laboratory at the University of Seville, led by Professor José Carlos GarcÃa Gómez, has been monitoring the spread of this algae for years. Their studies describe the phenomenon as an unprecedented colonization worldwide , with the capacity to cover 100% of the seabed in some areas. The species, native to the northwestern Pacific, likely arrived via the ballast water of merchant ships.
Since then, its advance has not stopped. It has spread to the five coastal provinces of Andalusia and has also colonized the coasts of Portugal and northern Spain. The annual biomass in the Strait is estimated at around 100.000 tons, a figure that varies depending on the winds and currents.
Impact on biodiversity and fishing
The algae form dense mats on rocky seabeds , suffocating the marine ecosystem and drastically reducing available light and space. Slow-growing native species, such as corals and sponges, are being displaced, along with sea urchins and mussels. In several areas studied, the seabed has become completely homogenized.
The fishing sector is also suffering the consequences. Studies indicate losses of between 50% and 100% in artisanal fishing of certain species in the most affected areas. Nets are being pulled from the water full of algae instead of fish, completely disrupting the Strait's productive dynamics.
Why is it impossible to eradicate it?
At first glance, it might seem that pulling up the algae or applying chemicals would solve the problem. But the scale is so enormous that any manual intervention is useless . Furthermore, local wildlife has shown no signs of adapting to prey on it. Although the common sea urchin feeds on it, its impact is minimal and does not reverse the invasion.
The species was included in the Spanish Catalogue of Invasive Alien Species in 2020, and in 2022 the European Union classified it as a species of concern. European regulations prohibit its exploitation while it retains the capacity to reproduce, to prevent a market from incentivizing its spread.
Control and valuation strategies
Given the impossibility of eradication, the RUGULOPTERYX project, led by the University of Málaga, uses supercomputing to model the algae's behavior and identify vulnerable areas in protected zones between the Strait of Gibraltar and the Balearic Islands. They rely on networks of sentinel stations to detect its arrival in new areas before they become overrun.
Another line of research is the valorization of biomass. IFAPA is leading projects to convert the algae into biofertilizers, biopesticides, compost, and extracts for grape cultivation. Its incorporation into fish feed for aquaculture is also being studied, where it has been shown to improve omega-3 levels, gut microbiota, and the immune response of the fish.
The cost to municipalities
Coastal municipalities bear the greatest financial burden. In Mijas, 1.890 tons of seaweed have been removed so far in 2026, at a cost of over €1,5 million, covered by the municipality's own funds. In Tarifa, last year's expenditure was around €300.000, with a subsidy of only €150.000 from the Cádiz Provincial Council.
The Andalusian Regional Government has declared a situation of 'force majeure and extreme necessity' to allow for the exemption of the state landfill tax, thus easing the economic pressure. Even so, the municipalities are demanding more aid and a long-term solution that involves finding an economic use for the seaweed.
Figures and expansion
The data reflects the magnitude of the problem. In Rota, the volume transported to landfill increased eightfold in 2025 compared to 2022. In Algeciras, removals were five times greater in 2025 than in 2023. Tarifa managed more than 11.000 tons in a single summer, and Marbella has recorded removals of hundreds of tons in a single day.
The expansion continues. In Huelva, the sandy seabed partially hinders its advance, but its presence continues to increase. Granada is widely affected, and in AlmerÃa the species maintains a significant presence in areas such as Aguadulce, Roquetas de Mar, and the Cabo de Gata-NÃjar Natural Park.
Forced coexistence with Asian seaweed is now a reality in Andalusia. While science seeks ways to contain its spread and utilize its biomass, municipalities remain the first line of defense. The battle will not be won through eradication , but through the intelligent management of a problem that is here to stay.