The invasive seaweed Rugulopteryx okamurae, of Japanese origin, has shown accelerated growth along the Sines coast over the past three years, warned researcher Joaquim Parrinha, collaborator at MARE|ARNET. The species was first detected ten years ago in the Setúbal district and, in the municipality of Odemira, has been found along the coastline between Melides and Azenha do Mar, with different levels of concentration. The seaweed is believed to have been introduced to the Mediterranean in 2022 through aquaculture oysters and was detected in the Azores in 2019, having first established itself in the Algarve before moving up the Portuguese coast, facilitated by rising water temperatures.
The accumulation on some beaches in the municipality of Sines results from sea agitation that tore the seaweeds from the seabed and transported them to the coast. In places like Ilha do Pessegueiro, there are authentic forests of this seaweed that, despite their beauty, are not natural for native species, compromising their development. Joaquim Parrinha explained that the accumulation prevents light passage and reduces oxygen availability on the seabed, with consequences for coralline algae, wracks, kelps and algae of the genus Codium. The large masses of seaweed form gas pockets that lead to eutrophication of subaquatic lagoons.
The researcher argues that it is necessary to remove this biomass from the beaches and potentially use it for agricultural purposes, or alternatively proceed with harvesting the seaweed on land or underwater to free up rocks for native seaweeds to attach to. This brown seaweed originates from the warm and temperate coasts of the Northwest Pacific and was first recorded in Europe at Étang de Thau, France, in 2002. Its proliferation occurred from 2015 onwards, colonizing rocky substrates between 0 and 40 meters depth, having recently reached Madeira, the Azores and the Canary Islands.
In July 2025, the Portuguese Government approved the National Strategy for the Management of the Invasive Macroalgae Rugulopteryx okamurae, which provides for mechanical removal of the seaweed in critical zones, study of its valorization for industrial or agricultural purposes, mobilization of regional rapid response teams and creation of a national database with georeferenced records of the species' evolution.
