Sushi Seaweed Threatens Biodiversity in Northern Portugal

CBMA and CIIMAR conduct the first local mapping of wakame and propose strategies to mitigate its impact on native species. This Monday marks World Wildlife Day.

A team from the universities of Minho and Porto has, for the first time, mapped the distribution of the invasive wakame seaweed—one of the world’s 100 most invasive species—along the northern coast of Portugal, highlighting its ecological impacts and proposing measures for control.

Wakame (Undaria pinnatifida) is rich in fibre, protein, vitamins, and minerals, particularly iodine and calcium. It is commonly used in East Asian cuisine, including sushi, and is believed to help prevent premature ageing, cardiovascular diseases, and aid in weight loss. Originally from East Asia, U. pinnatifida was introduced to France for commercial farming but escaped into the wild. It is thought to have reached Portuguese waters through ship ballast water and was first recorded in the country over 20 years ago.

The new study, published in the scientific journal Plants, was conducted by Marcos Rubal, Jesús Fernández-Gutiérrez, Diego Carreira-Flores, and Pedro Gomes from the CBMA at UMinho’s School of Sciences, along with Puri Veiga from the Interdisciplinary Centre of Marine and Environmental Research (CIIMAR) at UPorto. The research is part of the MarinaForest project, funded by the Portuguese Foundation for Science and Technology (FCT) and led by Veiga.

The research team found that the geographical distribution of wakame is significantly influenced by salinity, thriving in saltwater marinas such as those in Póvoa de Varzim and Leça da Palmeira, while being absent from estuarine marinas where salinity is lower. In natural habitats, the alga appeared temporarily in three rocky areas of Carreço and Canto Marinho but disappeared after winter storms.

“This species has limited tolerance to wave exposure, which restricts its spread to more exposed areas, but it may still pose a threat in sheltered environments,” says Marcos Rubal.

The study also found that Undaria pinnatifida replaced the native Saccharina latissima in marinas, where it also grew over mussels attached to artificial structures. In natural habitats, it was observed growing over the native species Gongolaria baccata. To mitigate these impacts, researchers conducted removal experiments at the Viana do Castelo marina. The results were promising, showing a partial recolonisation of S. latissima, suggesting that reducing wakame’s presence helps in the recovery of native species. This study provides essential data for effective strategies in marine ecosystem management and conservation.

Read the full press release in portuguese HERE .