Lisbon, Aug. 28, 2026 (Lusa) - The number of invasive marine species in Portuguese waters has risen by 75% in 10 years, with 98 additional records, according to a scientific study which Lusa saw on Friday.
This study updated a 10-year-old survey of «non-native or introduced species in Portuguese coastal waters, including estuaries, coastal lagoons and both the mainland and the islands», Paula Chainho of the Centre for Marine and Environmental Sciences (Mare), one of the organisations overseeing the project, explained to Lusa.
«We found that 10 years ago we had reported 133 non-native species and we have now reported 231», which corresponds to «a very high rate of new introductions», she said.
This «is even more noteworthy» because the researchers who carried out the study 10 years ago acknowledged that the high number recorded at the time corresponded to species that had not been studied, but everything indicates that these 100 new records represent a «quite sharp increase» because, since then, researchers have carried out several analyses.
«Of the 231 confirmed species, 159 are found in mainland Portugal, 81 in the Azores and 62 in Madeira», according to the presentation of the study by 31 researchers from 11 Portuguese universities and various organisations, led by Mare and the Aquatic Research Network (Arnet), which was published in the journal Marine Pollution Bulletin and highlights several problems along the Portuguese coast.
According to Paula Chainho, «shipping is the main cause of the introduction of new species», whether through species «fouling the hulls of vessels» or through the flushing of ballast water tanks.
Cargo ships have internal water tanks to maintain balance during loading and unloading, ensuring structural stability.
«When a vessel unloads a particular cargo, it has to compensate for that loss of weight with additional weight and, therefore, in this case, with the water introduced into the ballast tanks», which the vessel discharges at another point on the globe when it takes on new cargo.
«Many living organisms travel in this water, which is taken on board in one place and discharged in another,» explained the researcher, who also highlights risks to aquaculture.
At issue in these cases is the introduction of new farmed species, as well as organisms that «hitched a lift» on these specimens.
For this reason, «the focus must be primarily on prevention, because once an aquatic species enters a particular location, we will only detect it once it is already firmly established», the researcher told Lusa.
In this regard, there is an «international convention on ballast water that requires ballast water to be treated before being discharged», but «in Portugal we have no official reports we can consult on how this has been implemented».
As for aquaculture, «there are also regulations, and therefore a specific application is required to introduce a new non-native species for aquaculture», but «Portugal currently has no monitoring system to check whether this is being complied with», she said.
In other cases, species such as the Japanese clam, which has been present in Portuguese waters for many years, are managed through fisheries management, the researcher acknowledged.
The study also proposes a new watch list comprising 22 species detected via environmental DNA, an early-detection system capable of identifying invasive species before they can be observed with the naked eye.
In the waters off mainland Portugal, 39% of non-native species originate from the North Pacific, followed by 24% from other parts of the North Atlantic – a trend that is reversed in the Azores and Madeira, where the North Pacific predominates.
Of all the ports, Sines «emerges in the study as a strategic point of entry, given its location at the crossroads of maritime routes linking Asia, the Mediterranean, the United States and Africa», she noted, explaining the rationale behind the specific research into this area.
«Marine invasions are a dynamic and cross-border phenomenon, and understanding them requires a science capable of operating on the same scale. This study has enabled us to go far beyond a simple update of species numbers, revealing patterns of introduction, gaps in genetic knowledge and priorities for future monitoring,» said Romeu Ribeiro, a researcher at Mare and the study's lead author, in a press release.
The team developed a «pioneering watch list comprising 22 species detected exclusively through molecular methods, such as environmental DNA», even «without physical confirmation of their existence».
This mechanism constitutes «an early-warning system, capable of flagging potential invaders before they are visually identified in the field».
PJA/ADB // ADB.
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