How do we deal with invasive species?

Currently, invasive species are one of the main threats to biodiversity and the balance of ecosystems. Their introduction, usually accidental and associated with human activity, allows these species to spread easily and displace native fauna and flora. The environmental, economic, and health impacts of species such as the Asian hornet, the box tree moth, or the Senecio inaquidens, for example, are becoming increasingly severe and evident.

With this in mind, Prismàtic , the knowledge platform for the management of natural heritage and biodiversity, focused its annual conference on the management of invasive species. The event, held on January 20th at the Generalitat's Administrative District, attracted over 230 participants and once again demonstrated its potential as a forum for scientific, technical, administrative, and management discussions.

The presentations at this Prismàtic conference provided a comprehensive overview of Catalan research on invasive species, as well as the actions being taken to combat them. The official welcome address was given by Josep Planas, Deputy Director General of Environmental Policies and Natural Environment at the Department of Territory, Housing and Ecological Transition, who emphasized that invasive species are one of the causes of the decline in most flora and fauna populations in Catalonia, as detailed in the State of Nature 2020 report and corroborated by the Living Planet Index for Catalonia, published in early 2025.

The first presentation of this day on invasive species was given by Joan Pino, CREAF's director, who explained the work carried out by EXOCAT, a project to improve prevention and control strategies for biological invasions in Catalonia. Thanks to this tool, we know, among other things, that Catalonia has gained 631 alien species in 10 years, 21 of them invasive , and we have a blacklist of which of these taxa have been most frequently searched. When asked about CREAF's role in EXOCAT, Joan Pino noted that the ecology research center is just one component of this collaborative tool, and he invited anyone with data on invasive species in Catalonia to gave it to this platform in order to expand its knowledge and translate it into management practices.

Sònia Garcia, a researcher at the Botanical Institute of Barcelona (CSIC-CMCNB), explained the experience of the LIFE medCLIFFS initiative on the prevention and management of invasive species in the Catalan cliffs with Limonium spp. This habitat is generally in a poor state of conservation and is particularly vulnerable to biological invasions due, among other factors, to the impact of tourism. The LIFE medCLIFFS project has promoted tools for the prevention and rapid detection of invasive species, management and rapid response tools, and eradication measures. Specifically, the project has focused on eliminating invasive species in the most strategic conservation areas of Cap de Creus, rather than making a large investment to attempt complete eradication from all the studied sites. One of the most interesting prevention tools they have developed has been the lists of potentially problematic species for cliffs: the consensus list for the most problematic ones, the monitoring list for those that must be monitored and, in contrast, a white list of alternative taxa that can be sold and planted without any risk.

Fernando Loras, a researcher with the Catalan Herpetological Society, explained the critical situation of biological invasions affecting amphibians in Catalonia , which also suffer from the fragility and seasonality of some aquatic ecosystems . Specifically, Fernando detailed the status of some invasive species, such as the newt (Ommatotriton ophryticus x nesterovi) and the alpine newt ( Ichthyosaura alpestris ). These species have been studied and monitored in detail for their proper management, as until now there was very little information on their distribution and abundance. In conclusion, to improve the study and management of these species, Fernando recommended using the PACA (Persevere, Adapt, Communicate, and Update) methodology, combining capture methods, establishing different types of monitoring, and maintaining direct contact with local stakeholders . He also confirmed that, through genetic analysis, it is possible to determine the origin of the parent species of invasive hybrids, but that it is much more difficult to pinpoint the exact area from which they were introduced.

Focusing on a specific case of local management of a biological invasion, Marc Viñas , coordinator of the SEO/Birdlife technical office in the Ebro Delta, explained his experience with Cortaderia selloana, a plant from South America that is wreaking havoc on many aquatic ecosystems, riverbanks, and slopes. In the Ebro Delta, machinery was combined with volunteer labor and even livestock grazing to carry out large-scale eradication operations of invasive species. This required extensive outreach to identify the most problematic taxa and their locations. Regarding Cortaderia , it was crucial that volunteers learn to distinguish it from Saccharum ravennae, a native species with which it coexists and which is morphologically very similar. Marc's intervention at the Prismàtic conference concluded with the presentation of the transnational strategy to combat Cortaderia selloana in the Atlantic arc.

After a well-deserved coffee break, the presentations of the Prismàtic conference moved into the water. María García, a researcher at CEAB-CSIC, explained the management of invasive macroalgae species on the Catalan coast. Despite the serious effects of introducing invasive fish species such as Siganus, which prey on native algae to the point of leaving the seabed devoid of vegetation, the greatest impacts come from invasive macroalgae that have been monitored for over 30 years. The example of ecosystem resilience against Caulerpa cylindracea was particularly interesting. Populations of this invasive alga have decreased in recent years thanks to the salema porgy, a native marine herbivore which has learned to prey on it. María concluded her presentation by emphasizing the importance of citizen science carried out by Observadores del Mar (Sea Observers). Through this platform, for example, the first specimen in Barcelona of the exotic macroalga Asparagopsis taxiformis was detected: this is the species that appears on the poster for this Prismàtic event.

Emili García, a researcher at University of Girona, concluded the speakers' presentations by explaining how risk analysis and horizon scanning contribute to the management of invasive species. Risk analysis is the sum of risk assessment, primarily carried out by scientists based on biological and ecological criteria, and risk management, based on political decisions and implemented by administrations, technicians, and managers. Risk communication has recently been incorporated to facilitate the strategic exchange of information. All these protocols inform legislation, such as the expansion or modification of the Spanish Catalogue of Invasive Alien Species, which can be proposed by any citizen who believes that an alien species not currently included poses a significant risk.

Horizon scanning is a more recent methodology based on the systematic investigation of potential threats or opportunities, which Helen E. Roy adapted for invasive alien species. In this case, the process involves obtaining a list of potential invasive taxa, a simplified validation of their risks, and the creation of a ranked list by consensus among all the experts involved. In 2023, the first horizon scan of invasive alien species in Spain was carried out, identifying the 108 alien species with the highest risk of invading Spanish ecosystems. Emili García participated in this study, along with researchers from CREAF. This has led to an interesting debate about how to manage the territorial scale, since a species can be native in one region of the country and invasive in another region of the peninsula or the islands. Emili has stated that, given that environmental responsibilities are usually regional, legislation and management should attempt to encompass all possible territorial levels.

Following the presentations, the Prismàtic event featured an engaging panel discussion with Quim Portet, a technician from the Fauna and Flora Service of the Generalitat of Catalonia; Nati Franch, head of the Protection and Research Area of the Ebro Delta Natural Park; and Santiago Poch, project manager at the Emys Foundation. The panelists described the situation regarding invasive species as "dramatic" and "overwhelming," stating that we are constantly reacting to these invasions and that their management is severely hampered by a lack of funding and, in unprotected natural areas, the absence of a dedicated management institution. To decide what to prioritize, the speakers proposed focusing efforts on small, isolated, and strategic locations, such as aquatic habitats like ponds or wetlands, although this becomes much more complicated in areas of high ecological connectivity like the Ebro Delta. They also emphasized the importance of prevention to eliminate the problem before it arises, the value of having a comprehensive ecosystem restoration plan for the areas where interventions take place, and containing the expansion fronts of invasive species as fundamental strategies against them. Conversely, when asked which actions should be discontinued, the speakers suggested eliminating actions that cannot be decisive, those carried out from inertia and that could be counterproductive, or those linked to one-off projects with limited funding that do not allow for subsequent management of the natural area where intervention has occurred.

Joan Pino, moderator of the engaging panel, questioned whether these poorly executed conservation efforts could be due to the lack of a comprehensive action plan for invasive alien species. The panelists responded by asserting that what is needed are “more concrete actions on the ground and not so many plans and regulations” that are sometimes never implemented, as well as the need for integrated coordination among entities, government agencies, the agricultural sector, local communities, and so on.

One of the most interesting parts of the Prismàtic event was when the audience joined the engaging panel discussion. While some attendees called for more decisive action in resilient ecosystems like those of the Mediterranean Sea, others questioned whether we shouldn't accept that, in many cases, invasive species will eventually find a balance within the ecosystem on their own. As always, the open debate wasn't without controversy, and one attendee challenged the selection process for which invasive alien species should receive priority management, arguing that species like the native crab shouldn't be protected as much as they currently are.

In this tone of protest, speaker Fernando Loras expressed his concern regarding the timeframes for some requests for action against invasive species. The final intervention from the audience clarified that nature management and conservation interventions unrelated to invasive species, such as fire prevention measures, should also aim to prevent the exacerbation of these biological invasions. Ideally, these actions should even work synergistically to eradicate invasive species.

The Prismàtic event concluded with a positive assessment from Marc Vilahur, Director General of Environmental Policies and Natural Environment of the Department of Territory, Housing and Ecological Transition of the Generalitat of Catalonia.

On the other hand, once the conference was over, the CREAF director, Joan Pino, described it as a success and stated that "it has been useful to advance in the analysis of the situation of biological invasions in Catalonia and in a sharing of its management strategy: what we should prioritize, what we should stop doing and where we need to move forward."