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Europe Diabrotica virgifera

11,000 alien species invade Europe; how will Europe respond?

Recent data on alien species present in Europe and their impacts provide a basis for strengthening European policies on biological invasions

Europe’s borders have been breached by thousands of plants and animal species from other parts of the world: from the American mink to the New Zealand flatworm. The invaders feed on, hybridise with, parasitise and out-compete native species. They also introduce diseases, alter the balance within ecosystems, modify landscapes and impact upon agriculture, forestry and fisheries.

More than 11,000 alien species have been documented by DAISIE (; DAISIE Handbook of Alien Species in Europe), a three year research project which was commissioned by the European Union to a consortium of leading scientists including ISSG, to survey invasive species across Europe and assess their ecological and economic impacts. Thanks to the much more detailed information now available, ecologists have begun to assess the magnitude of this damage in Europe. In a recent paper (Vilà et al. 2009) European researchers have assessed which species have the most impacts in the region. Among the top invaders were Canada geese, zebra mussels, brook trout, the Bermuda buttercup and coypu, also known as nutria. Terrestrial vertebrates produce the widest range of impacts, often showing effects in all of the ecosystem service categories. Many terrestrial vertebrates are top predators, and their introduction causes cascading effects in the food web. By contrast, terrestrial invertebrates such as insects and spiders had the narrowest range of effects, but wreaked the most financial havoc. Terrestrial invertebrates cause the most damage to crops and forests, sectors in which there are well-established methods to quantify the costs of food and lumber production. Yet for 90% of species almost nothing is known of their impacts. Vilà and co-authors estimate annual crop losses in the United Kingdom due to alien arthropods at €2.8 billion (about $3.7 billion), and the cost of eradicating the 30 most common weeds could be more than €150 million ($197 million).

The authors focused their assessment on impacts on ecosystem services. Ecosystem services were broken down into four categories: supporting major ecosystem resources, such as water and energy cycles; provisioning by producing goods, such as pollination of crops; regulating ecosystem processes, such as water filtration; and cultural or non-material benefits, such as recreation and aesthetics. Yet they also present data on some of the alien species generating the highest reported financial investment, including costs of monitoring, controlling and eradicating the invader, along with environmental education programs. Among the most expensive invaders were water hyacinth (€3.4 /$4.5 million), coypu (€2.8/$3.7 million) and a marina alga (€8.2/$10.9 million).

Using these data and additional information on known management costs in Europe, Kettunen et al (2008) have provided preliminary estimates indicating that the monetary cost of invasions in Europe amounts to at least €12 billion per year.

The data collected by the DAISIE program have also shown that a significant proportion of the impacts recorded in Europe happen in the marine environment. Introduction in European seas are partly due to intentional introductions occurred for aquaculture purposes or stocking for (game) fisheries, but mostly happening unintentionally, through the release of organisms transported in the ballast water of ships or because ships carry organism in the fouling of the hull. To respond to these threats, he International Maritime Organization (IMO, the United Nations body to deal with shipping), prepared the Ballast Water Management Convention, which has so far been ratified by only two European states.

These data bridge a gap in knowledge that has contributed to the so far scarce efforts put in place by European countries to prevent and control invasions. The evidences of increasingly disastrous effects of invasions for Europe’s biodiversity, health and economy have helped convincing the European decision makers that it is urgent to develop a coordinated and stringent policy on the issue. The European Commission has adopted in last 3 December 2008 a Communication stressing the need to urgently develop by 2010 a European Strategy on Invasive Species, and outlining three potential ways forward, each representing a different level of legislative cost and complexity.

One of the key elements stressed by the Communication is the need to establish a European early warning and rapid response framework to tackle new invasions, and the European Environmental Agency is now working at outlining possible options to create such structure (Genovesi et al. 2009). A recent response to the Communication, published in Science (Hulme et al. 2009) has highlighted the challenges facing Europe in delivering a European Strategy on Invasive Species. Existing legislation could be adapted by establishing “blacklists” of species prohibited from import and sale in Europe. However, pan-European bodies have been unable to agree on criteria for the list. This problem is exacerbated because a significant proportion of alien species in European countries are native elsewhere on the continent. For example, the Spanish slug is now causing problems as an agricultural and garden pest in the UK, Denmark, Germany and Scandinavia, among other regions. Therefore blacklists may need a regional focus. Hulme et al. 2009 suggest that centralised management of this increasingly important issue should be a priority and call for the establishment of the European Centre for Invasive Species Management.

The authors acknowledge that such a centre would face challenges. This is particularly because the free EU market for goods and people tends to encourage the spread of invasive species; regulation may be seen as a barrier to economic growth. However, action must be taken, say the researchers. They suggest that the cost of a centre would amount to less than 0.5 per cent of the annual costs of invasions and could bring greater returns to the European economy and environment.

Europe seems at last to have become aware of the threats posed by increasing invasions to its biological diversity, well-being and economy, but only time will tell us if the European institutions and society will be able to meet this challenge.

Piero Genovesi
(Chair ISSG) with contributions from Stephan Gollasch, Phil Hulme, Wolfgang Nentwig, Petr Pysek, David Roy (DAISIE)

DAISIE (2009) Handbook of Alien Species in Europe. Springer, Dordrecht. ISBN 978-1-4020-8279-5 Hulme P.E., Pyšek P., Nentwig W. & Vilà M. (2009) Will threat of biological invasions unite the European Union? Science 324, 40-41.

Kettunen, M., Genovesi, P., Gollasch, S., Pagad, S., Starfinger, U. ten Brink, P. & Shine, C. 2008. Technical support to EU strategy on invasive species (IS) - Assessment of the impacts of IS in Europe and the EU (Final module report for the European Commission). Institute for European Environmental Policy (IEEP), Brussels, Belgium. 40 pp. + Annexes, May 2008, (DG ENV contract).

Vilà M., Basnou C., Pyšek P., Josefsson M., Genovesi, P., Gollasch S., Nentwig W., Olenin S., Roques A., Roy D., Hulme P.E. & DAISIE partners (2009) How well do we understand the impacts of alien species on ecosystem services? A pan-European cross-taxa assessment. Frontiers in Ecology and the Environment, online

Genovesi et al. (2009) Towards an early warning and information system for invasive alien species (IAS) threatening biodiversity in Europe. ISPRA, (EEA Contract).