Healthy thalli of the invasive seaweed Rugulopteryx okamurae (Phaeophyceae) being massively dragged into deep-sea bottoms by the Mediterranean Outflow Water

The invasive seaweed Rugulopteryx okamurae has recently arrived in Europe from the western Pacific. Its explosive spread on coastal areas of the Gulf of Cadiz (GoC), Strait of Gibraltar and Alboran Sea is spoiling native coastal ecosystems and inflicting heavy losses on ecosystem services. We discovered for the first time large amounts (up to 17 g m(-2)) of detached R. okamurae thalli on deep-sea bottoms of the GoC that are being dragged from the Strait of Gibraltar shores into the NE Atlantic by the Mediterranean Outflow Water (MOW). Laboratory experiments revealed that collected unattached macroalgae from deep-sea locations were alive and healthy and maintained intact photosynthetic capacity after long dark periods, suggesting a tremendous resilience and invasive potential. Given the rapid transport of healthy thalli by the MOW and massive accumulation of them in the GoC basin, R. okamurae could represent a major threat to NE Atlantic ecosystems, affecting not only coastal but also deep-sea habitats.

Automated summary

The invasive seaweed Rugulopteryx okamurae has recently spread to Europe from the western Pacific, causing damage to native coastal ecosystems and ecosystem services. Large amounts of detached thalli of R. okamurae were found on deep-sea bottoms of the Gulf of Cadiz, indicating a potential threat to both coastal and deep-sea habitats. Laboratory experiments showed that the collected unattached macroalgae from deep-sea locations were healthy and capable of photosynthesis even after long periods of darkness, indicating their resilience and invasive potential.