Non-native species assessment of Spanish transitional waters (between land and sea) recommends proactive management

Colonisation of natural habitats by non-native species has played a role in 33% of all recent animal extinctions and can cause substantial ecological and economic damage. Non-native species are commonly known as invasive alien species (IAS) when they are introduced, either accidentally or deliberately, into a given ecosystem and become harmful for native biodiversity. Invasive species can prey upon or displace indigenous plants and animals, including those that are threatened or support human activities and livelihoods.

Removal of established alien species populations is costly and rarely successful. Global expenditure on invasive species management has totalled US $95.3 billion (€87.03 billion) since 1960¹, with damage due to invasive species costing US$1 130 billion (€1 031 billion) over the same period. For instance, the management of the non-native zebra mussel (Dreissena polymorpha) in the Ebro River Basin, Spain, involved €11.6 million in combined control and damage costs over the period 2005–2009. Efforts to prevent introduction or spread of invasive species typically comprise cheaper and more effective options, but preventive actions are less commonly undertaken. Such actions are most effective when based on an understanding of how non-native species arrive and spread.

The EU’s Invasive Alien Species (IAS) Regulation includes measures to manage established invasive alien species and to reduce the number of Red List species that they threaten by 50% by 2030. These measures include the requirement for Member States (MSs) to act on possible routes of unintentional introduction of alien species, to rapidly detect and eradiate these species and to manage species that are already widespread.

The Mediterranean Sea is a global hotspot for invasive species with over 1 000 reported and at least half of these already established in some areas. Transitional waters where fresh- and salt-water meet, such as estuaries, deltas, marshes and coastal lagoons, can be especially vulnerable as they may host both freshwater and marine species as well as transitional water species (i.e. estuarine species). Ecological assessments of transitional waters for the European Water Framework Directive and the European Marine Strategy Framework Directive specifically require information on non-native species. However, comprehensive reviews of such data are often lacking.

This study, partially supported by the EU LIFE Programme², compiled information on non-native animal species recorded at 30 key transitional sites on the Spanish Mediterranean coast (including the Balearic Islands). The researchers gathered data from an extensive review of published scientific articles, grey literature (published studies not in peer-reviewed journals) and online and institutional databases. They recorded the pathway or pathways by which each species arrived to the study area, using the Convention on Biological Diversity classification scheme. They also evaluated species as established (known to have at least one self-sustaining population in the region), uncertain (recorded occasionally but with no self-sustaining population) or cryptogenic (status could not be determined from available information).

The researchers identified 129 non-native animal species across the sites, 72% of which were established. Of the total, 53 were vertebrates (28 of which were ray-finned fish, Actinopterigii), 34 were molluscs (19 gastropods and 15 bivalves) and 26 were arthropods (mostly crustaceans). The most common species was the Asian tiger mosquito (Aedes albopictus), which was found at every site, but also the Eastern mosquitofish (Gambusia holbrooki), the red swamp crayfish (Procambarus clarkii) and the Atlantic blue crab (Callinectes sapidus), which were recorded in the vast majority of sites. The Ebro Delta Natural Park in Catalonia had the highest number of non-native species (84), with the number of species recorded at each site generally decreasing southward and a low invasive-species richness detected in Andalusian transitional waters.

The researchers identified four main pathways³ as contributing to 84% of all introductions. They grouped these either as accidental – stowaways (contributing to 78 introductions) and contaminants (contributing to 68) – and deliberate or intentional – escapes (75) and releases (61). The intentional pathways were by far the most important for vertebrates, say the researchers, resulting especially from recreational fishing and the pet/aquarium trade (in particular freshwater turtles), while the accidental pathways were more common for arthropods.

The researchers say that Catalan sites, especially the Ebro Delta, appear to be critical gateways for the arrival of non-native species to the Spanish Mediterranean coast. They also highlight that 23% of the identified species presented ‘uncertain’ establishment status, making them a potential risk for fully establishing in the near future.

The researchers call for a more proactive monitoring programme⁴ targeting invasive species in the study area. They recommend that this includes the use of environmental DNA techniques (detecting species presence through DNA traces in water samples), the implementation of early warning and rapid response protocols (such as the North American system trialled in La Spezia, Italy⁵) and promoting the use of anti-fouling paints on ship hulls to minimise stowaway introductions. They suggest that a similar programme would benefit many areas of Europe’s Mediterranean coast where invasive-species risks are likely to follow similar patterns.

The researchers also highlight the use of grey literature providing records of non-indigenous species – such as bulletins and technical reports, and independent databases as key resources for collecting comprehensive data and recommend that future assessments follow this methodology. They also suggest that future assessments should also account for invasive plant species to provide a more reliable and integrated understanding on the magnitude of biological invasions in transitional waters.

Footnotes:

1. For more information see: IPBES (2023). Summary for Policymakers of the Thematic Assessment Report on Invasive Alien Species and their Control of the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services. Roy, H. E., Pauchard, A., Stoett, P., Renard Truong, T., Bacher, S., Galil, B. S., Hulme, P. E., Ikeda, T., Sankaran, K. V., McGeoch, M. A., Meyerson, L. A., Nuñez, M. A., Ordonez, A., Rahlao, S. J., Schwindt, E., Seebens, H., Sheppard, A. W., and Vandvik, V. (eds.). IPBES secretariat, Bonn, Germany. https://zenodo.org/record/8314303
2. See: the LIFE Invasaqua project.
3. The Invasive Alien Species (IAS) Regulation requires that EU Member States set up pathway management plans.
4. The IAS Regulation requires MSs to set up IAS surveillance systems.
5. See: Tamburini, M., Keppel, E., Marchini, A., Repetto, M. F., Ruiz, G. M., Ferrario, J., and Occhipinti-Ambrogi, A. (2021) Monitoring non-indigenous species in port habitats: First application of a standardized North American protocol in the Mediterranean Sea. Frontiers in Marine Science, 8. Available from: https://doi.org/10.3389/fmars.2021.700730

Source:

Zamora-Marín, J.M., Herrero-Reyes, A.A., Ruiz-Navarro, A. and Oliva-Paterna, F.J. (2023)

Non-indigenous aquatic fauna in transitional waters from the Spanish Mediterranean coast: A comprehensive assessment. Marine Pollution Bulletin 191: 114893. Available from: https://doi.org/10.1016/j.marpolbul.2023.114893 [Accessed 1 August 2023].

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“Science for Environment Policy”: European Commission DG Environment News Alert Service, edited by the Science Communication Unit, The University of the West of England, Bristol.

Notes on content:

The contents and views included in Science for Environment Policy are based on independent, peer reviewed research and do not necessarily reflect the position of the European Commission. Please note that this article is a summary of only one study. Other studies may come to other conclusions.