By John Dawes

There are more than 10,000 alien or exotic species in Europe. In fact, the Delivering Alien Invasive Species Inventories for Europe (DAISIE) project lists more than 11,000 in its database, following a three-year research program funded by the European Union that involved more than 100 scientists.

Procambarus clarkii, the Louisiana red swamp crayfish, was once popular in the aquatic hobby, but most European countries have now banned it.

Nevertheless, it also states that, prior to the publication of its database, “the number and impacts of harmful alien species (also called invasive alien species) in Europe has been underestimated.”

This lack of knowledge has, according to the project, “contributed to inaction in many European countries, which is becoming increasingly disastrous for Europe’s biodiversity, health and economy.”

All individual species are reviewable on the DAISIE website. However, there is a highlighted separate list of the 100 most invasive ones, each featured species with its own entry.

Six species that are of interest and/or relevance to the ornamental aquatic sector appear on this “hot” list of 100 invaders: two marine algae, Caulerpa taxifolia and C. racemosa var. cylindracea; two freshwater plants, Elodea canadensis and Crassula helmsii; a freshwater crayfish, Procambarus clarkii, and a freshwater cyprinid, Pseudorasbora parva.

Perhaps, a little surprisingly, the water hyacinth, Eichhornia crassipes, is not among the top 100 invaders, despite its widespread non-native European presence. Neither are the mosquito fish (Gambusia affinis and G. holbrooki), although they are among the most widely introduced fish globally.

Despite this, and other, shortcomings, the DAISIE database, which was only completed in November 2008, is already serving as a valuable reference for other studies, the most recent of which has been carried out by Montserrat Vilà, from the Estación Biológica de Doñana, in Seville, Andalucía (southern Spain), and a team of 10 other scientists. In a paper published on April 29, 2009, in Frontiers in Ecology and the Environment, Vilà and her team put prices on the damage caused by invasive alien species.

According to the team, for instance, alien arthropods (mostly insects) cause food-crop losses of €2.8 billion (U.S. $3.7 billion) per year in the U.K. alone, while, according to other studies, the cost of eradicating the 30 most common weeds could be as high as €150 million (U.S. $197 million).

Against this, the price of species that we, in the ornamental aquatic sector, are familiar with may seem relatively modest…but it is not. For example, eradicating or controlling two of these, the water hyacinth and what is referred to as “a marine alga.” Almost certainly Caulerpa taxifolia and C. racemosa, could cost as much as €3.4 million (U.S. $4.5 million) and €8.2 million (U.S. $10.9 million), respectively. <HOME>

First a schoolteacher, then a university lecturer, John Dawes is now a consultant and author with more than 4,000 articles and 30 books to his name. He holds Fellowships of the Zoological Society of London and the Linnean Society, Membership of the Institute of Biology and is a Chartered Biologist. He currently resides in Malaga, Spain.