Kategorie: News
Fishermen and Researchers Sound the Alarm
Off the Portuguese coastal city of Sines, an invasive brown algae has been spreading at an alarming rate for the past two to three years. Rugulopteryx okamurae, native to the northwestern Pacific (Japan, Korea, China), was first detected in the region around the Sines marina about ten years ago.
According to Joaquim Parrinha of the University of Coimbra and the MARE Marine Research Center, there have been constant sightings since it was first detected. However, it was only in the last two to three years that the population grew explosively.
An Import via a Detour Through France
The species arrived in Europe as early as 2002—presumably unintentionally, along with Pacific oysters imported into the Thau Lagoon in southern France. For over a decade, it remained a small, inconspicuous population there before spreading rapidly starting in 2015 along the Mediterranean coast of Spain to the Strait of Gibraltar. From there, it spread both further into the western Mediterranean and into the Atlantic—along the Spanish and Portuguese Atlantic coasts, where it initially took hold in the Algarve and subsequently advanced northward as far as the region around Sines.
The algae also reached the Atlantic islands of the Azores, the Canary Islands, and Madeira, where it is now considered established. The EU also lists the species as one of EU-wide significance, whose spread is to be contained.
When the seabed disappears beneath algae
The coastal stretch between Melides and Azenha do Mar is particularly affected, with dense populations especially near São Torpes and Ilha do Pessegueiro. Heavy swells tear the algae mats from the seabed, and southeasterly winds wash them ashore. According to Parrinha, the algae has already completed three full reproductive cycles this year alone—researchers therefore expect further growth in the coming years.
Underwater, the algae prefer to settle on rocks and in depressions in shallower areas, where they block light and oxygen exchange. Native algae species are bleaching under the dense blanket, and many animals are retreating to deeper, still-uncovered zones. The seafloor can be almost completely covered down to a depth of about twelve meters; below that, the growth usually thins out significantly.
The local fishing industry is also affected: nets are increasingly getting caught in the algae, while, according to fishermen, fish and octopus populations are retreating from the most heavily infested coastal areas.
Eradication Unrealistic, Control Is the Goal
Experts consider the complete removal of the algae to be practically impossible. Several Portuguese coastal municipalities, including Sines, are therefore participating in a funded project under the Algarve 2030 program, which aims to develop containment strategies in collaboration with research institutions such as MARE and the University of Minho. The plan ranges from regular cleanup of affected areas and scientific monitoring to the economic use of the resulting biomass, for example, as fertilizer or in biotechnological applications.
For divers planning to visit the region, this means one thing above all: Anyone heading to shallow rocky sites should check with the local dive center in advance to find out how severely the specific spot is currently affected—the situation can vary significantly from bay to bay.
Further information:
Público
Observador
Tribuna Alentejo