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Invasive alien species: biodiversity at risk

Invasive alien species: biodiversity at risk


Ana María Pujante Mora

Invasive alien species are animals, plants, or any other organism capable of establishing and spreading in other countries or regions, causing significant damage to local biodiversity. Law 42/2007 of 13 December 2007 on Natural Heritage and Biodiversity defines an invasive alien species as “a species that is introduced or established in a natural or semi-natural system or habitat and is an agent of change and threat to native biological diversity, either because of its invasive behaviour or because of the risk of genetic contamination”.

According to the latest IPBES (Intergovernmental Science Policy Platform on Biodiversity and Ecosystem Services) report of 4 September 2023, more than 37,000 invasive species have been introduced by human activities across all regions and ecosystems of the Earth. 3,500 are considered invasive alien species, due to evidence of the negative impacts they cause. This report estimates that the annual cost of biological invasions in 2019 was more than $423 billion. In Europe, the total costs of the impact of IAS between 1960 and 2020 have been assessed at around 116.61 billion euros (Economic costs of invasive alien species across Europe).

How do you know if a species is an invasive alien species?

For a species to be considered an invasive alien species, a scientific argumentation model must be completed with the proposal for the inclusion or exclusion of taxa and a technical report with the risk analysis that will be evaluated by a Scientific Committee. In Spain, all invasive alien species are included in the Catálogo Español de Especies Exóticas Invasoras, which is a dynamic tool that can be permanently modified. At present, this catalogue includes 199 invasive alien species:

Number of taxa included in the Spanish Catalogue of Invasive Alien Species

Routes of introduction/dispersal

The graph below details the main pathways of intentional and unintentional introduction of invasive alien species into Europe:

Categories of pathways of introduction of invasive alien spcies in the European Union (Source: Plan de acción sobre las vías de introducción y propagación de las EEI en España)

Examples of intentional introductions include:

  • Aquaculture (red swamp crayfish, river signal crayfish, rainbow trout)
  • Horticulture (water hyacinth)
  • Pets (Florida pond turtle, Kramer’s parrot, Vietnamese pig)
  • Sport fishing (catfish, perch, pike)
  • Biological control (gambusia)

Others have been introduced accidentally due to trade and transport of goods between different countries: zebra mussel, asiatic clam, red palm weevil, asian tiger mosquito, asian wasp (recently detected for the firt time in the Valencian Community).

Impacts and threats

The spread of invasive alien species is the second cause of biological biodiversity loss, second only to the destruction or alteration of natural habitats. The intensity and magnitude of disturbances depend on the invasive species and the ecosystem in which they are established, mainly due to:

  • Predation on native species
  • Displacement of native species
  • Food web effects
  • Disease transmission
  • Alterations to the gene pool

The economic damage caused by some of these invasive alien species in Spain is enormous:

  • Removing zebra mussels (Dreissena polymorpha) costs more than 40 million euros a year.
  • The removal of the water hyacinth (Eichhornia crassipes) from the Guadiana river has cost more than 50 million euros.
  • The damage to rice fields alone caused by the presence of the red swamp crayfish (Procambarus clarkii) is 4.5 million euros per year.
The red swamp crayfish (Procambarus clarkii) causes enormous environmental and economic damage in Spain

Control measures

The fight against invasive alien species must be approached from four fundamental aspects:

  • Prevention
  • Early detection
  • Effective control
  • Mitigation of impacts

To tackle the fight against invasive alien species and the effects they cause, the different national and regional administrations have drawn up Strategies and Plans that define the guidelines and priority lines of action. These lines of action are aimed at:

  • Define the most appropriate control mechanisms where the presence of the invasive alien species has been established.
  • Prevent occurrence in new areas.
  • Attempt to reduce its negative effects.
Example of mitigation of the effects of an invasive alien species on the banks of the River Turia with an action on the reed (Arundo donax).

What to do if a new invasive alien species is detected, especially if it is included in the Catálogo Español de Especies Exóticas Invasoras?

  • Contact the environmental authority of the corresponding Autonomous Community.
  • Notify the Ministerio para la Transición Ecológica y el Reto Demográfico (Subdirección General de Biodiversidad Terrestre y Marina,