Portugal takes proactive approach to invasive seaweed

The invasive Asian seaweed Rugulopteryx okamurae is expected to remain a feature of Portugal’s coastline for the foreseeable future, but scientists, local authorities and the government are increasingly focusing on monitoring, control and potential commercial uses for the species rather than attempting the impossible task of eradication.

According to a report by Público, researchers warn that the algae continues to spread along the Portuguese coast, particularly in the Algarve and Cascais. First identified in European waters in France in 2002, the species has now reached Sweden, Italy, Greece, Morocco, and the Portuguese Archipelagos of Madeira and the Azores.

Speaking at a conference held at Portimão Museum in May, Rui Santos, a researcher at the University of the Algarve’s Centre for Marine Sciences (CCMar), said the species is reproducing at an extraordinary rate.

“The algae contributes a further 500,000 individuals per square metre every year,” he explained, warning that rising sea temperatures and increasing atmospheric CO2 concentrations are likely to accelerate its growth.

Yet despite the scale of the challenge, experts believe the focus should now be on managing the algae’s impacts and exploring ways to turn the problem into an opportunity.

One possibility involves using the biomass to produce biomethane through dedicated biorefineries. Researchers are also studying potential agricultural applications for the seaweed, although changes to European legislation governing invasive species may be required before commercial uses can be fully developed.

“We need to find ways to harness the algae,” Santos argued.

The Portuguese government has already moved in this direction. Last year it approved a National Strategy for the Management of the Invasive Macroalgae Rugulopteryx okamurae, establishing a coordinated framework for monitoring, removal, scientific research and biomass valorisation.

The strategy, coordinated by the Portuguese Environment Agency (APA), brings together scientific institutions, municipalities and maritime authorities to develop practical responses to the growing problem.

Environment Minister Maria da Graça Carvalho said at the launch of the strategy that the government was acting “on the basis of the best available scientific evidence” to protect coastal ecosystems, fishing communities and tourism.

Among the measures included are mechanical removal in critical areas, rapid-response regional teams, scientific monitoring programmes and the creation of a national georeferenced database tracking the algae’s spread.

For Algarve municipalities, the issue has become increasingly familiar.

Lagoa mayor Luís Encarnação told journalists that around 40,000 tonnes of seaweed were removed from Carvoeiro Beach alone during the summer of 2024. “Our municipality has 15 beaches, but we were only able to bring heavy machinery onto Carvoeiro Beach,” he said. The collected algae, mixed with sand, had to be transported to landfill.

Similar operations have taken place elsewhere. In Cascais, around 1,300 tonnes were removed last year at a cost of approximately €500,000.

Encarnação believes greater emphasis should be placed on intercepting the algae before it reaches the shoreline.

“The national strategy must consider the possibility of removing it while it is still in the water column,” he said.

The mayor also highlighted concerns raised by local fishermen regarding the impact on marine ecosystems.

“There are species that have simply disappeared from our coast,” he said, citing sea urchins, razor clams, crabs and spider crabs. Reports have also emerged of octopuses being found dead in their dens, possibly linked to oxygen depletion caused by dense seaweed accumulations.

Despite these concerns, authorities stress that a coordinated response is now in place.

APA is expected to finalise its national mitigation and monitoring plan this summer, providing a clearer framework for long-term management.

Scientists acknowledge that Rugulopteryx okamurae is unlikely ever to disappear from Portuguese waters. However, with improved monitoring, faster response mechanisms and ongoing research into commercial applications, the emphasis is shifting from crisis management towards adaptation and control.

For coastal communities in the Algarve, that may ultimately prove the most realistic — and most effective — solution.

Source: Público; Portuguese Government

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