The invasive seaweed Rugulopteryx okamurae has recently established a foothold in European waters, arriving from the Western Pacific. Its rapid spread along the coasts of the Bay of Cádiz, the Strait of Gibraltar, and the Alborán Sea is undermining local coastal ecosystems and eroding the services these environments provide. This trend has become a growing concern for marine communities, fisheries, and coastal management across the region.
Researchers from the Málaga and Cádiz oceanographic centers of the Spanish Institute of Oceanography (IEO, CSIC) worked with the University of Málaga on the study now published in Phycologia. The study documents the aggressive expansion of Rugulopteryx okamurae and highlights its potential to disrupt biodiversity and habitat structure across both shallow and deeper marine zones.
In the Gulf of Cádiz, scientists detected substantial amounts of sap linked to Rugulopteryx okamurae washed through the Strait of Gibraltar toward the Northeast Atlantic. The researchers describe a transport pathway driven by Mediterranean outflow that carries thalli far from their original shores, underscoring the species’ capability to disperse over large distances via currents and water exchanges.
Laboratory tests showed that macroalgae collected from deeper locations remained alive and preserved their photosynthetic capacity even after extended periods in darkness, signaling a remarkable resilience and invasive potential for Rugulopteryx okamurae. This resilience means the algae could survive in less favorable conditions and potentially establish new pockets of invasion if left unchecked.
Work conducted in Tarifa documented ongoing efforts to eradicate the invasive alga from affected coastal zones. The findings emphasize the speed and extent of the species’ spread, prompting researchers to urge proactive monitoring and management to limit ecological damage and protect coastal economies dependent on healthy marine habitats.
Given the rapid movement of healthy thallus material from the Mediterranean outflow and the notable accumulation in the Gulf of Cádiz, Rugulopteryx okamurae represents a significant threat to Northeast Atlantic ecosystems. The invasion affects not only nearshore habitats but also deep-sea environments, where the consequences are less understood and potentially severe.
Deep-sea observations reveal thalli at depths reaching over 1,141 meters, while large accumulations of the invasive alga have become common along the Andalusian coast, presenting extensive brown-silhouette incursions along the shoreline and beyond.
Negative impact on habitats
The debris that remains on coastal zones originate from the seafloor where this alga grows. When thalli detach, tidal forces and currents can transport them to accretion sites, creating disturbances that ripple through local habitats and ecosystems. These impacts extend beyond beaches and shallow sediments to deeper regions where drifting fragments can disrupt seabed communities.
Researchers note that such drift can push into deep-water habitats, forming large accumulations that alter habitat structure and biodiversity. The Spanish Institute of Oceanography described this as a broad threat to both shallow and deep ecosystems in the Gulf of Cádiz, urging careful monitoring and rapid responses to curtail adverse effects.
The authors stress the urgency of controlling invasive species in these marine environments, advocating for measures that protect the health and biodiversity of both coastal and offshore ecosystems in the region.
Ángel Mateo, the lead author, highlights the significance of documenting these dynamics. The study emphasizes the need to safeguard the Gulf of Cadiz’s entire ecosystem, from beaches to the deepest zones, to maintain ecological balance and resilience.
The spread of Rugulopteryx okamurae is further illustrated by photographs showing Chinarral beach in Algeciras overrun by the alga in some zones, a striking example of the scale of invasion and its visual impact on coastal landscapes.
Researchers warn that suspended thalli carried by the Mediterranean outflow can become entangled with rocks, Marine debris, and both moving and sessile benthic organisms, creating complex interactions that may alter species relationships and habitat access for native communities.
Underwater imagery from the study captured numerous deep-sea habitats with abundant thalli tangled with corals, sponges, and gorgonians. The presence of Rugulopteryx okamurae in these environments signals potential disruption to sensitive species and community structures in both shallow and deep zones.
Some affected species are highly sensitive to physical disruption, including eight corals and delicate invertebrates such as isidella elongata and gracilis, as well as more resilient organisms like certain gorgonians and sponges. The invasion could alter the balance of these communities, shifting interactions and competitive dynamics among resident species.
toxic molecules
Beyond physical disruption, the invaded ecosystems may suffer from chemical effects. Several species appear on conservation lists due to declines linked to human pressures, including bottom-trawling activities that impact deep-sea habitats. Isidella elongata, a bamboo coral, is listed on Appendix II of the Barcelona Convention and on the IUCN Red List as Critically Endangered, highlighting the fragility of affected deep-water communities.
Rugulopteryx okamurae has been observed attaching to colonies like isidella elongata, potentially hindering growth and compromising the structural integrity of these slow-growing species, particularly at apical regions where coralline polyps occur. The full consequences of these interactions remain to be fully understood, necessitating ongoing research.
In addition to direct physical damage, decomposing thalli may release bioactive terpenoids with toxic effects on invertebrates that encounter them. These secondary metabolites can deter predators, interfere with larval settlement, or even cause harm, adding another layer of risk to affected communities.
The study provides evidence that Rugulopteryx okamurae can attach to sea urchins, sea anemones, sponges, and deep-sea gorgonians. Given the potential toxicity of its secondary metabolites, there is concern about adverse effects on these organisms, warranting further investigation into ecological interactions and outcomes.
The authors call for future research to examine Rugulopteryx okamurae not only in coastal and neritic zones but also in more bathyal depths, aiming to inform management strategies and mitigation efforts across a range of marine habitats.
Reference note: this study is published in a scholarly journal and is accessible through academic databases. Ongoing work continues to document the spread, ecological effects, and potential management responses to Rugulopteryx okamurae in the Northeast Atlantic and adjacent regions. .