Alien Invertebrates and Fish in European Inland Waters

It seems axiomatic that rivers, lakes, freshwater marshes, and other inland wetlands have an infinite value to humankind. They contribute for 20% (about US$6.6 trillion) to the estimated annual global value of the entire biosphere (Costanza et al. 1997). High-quality water has also become a strategic factor that allows for the viability and development of an increasing number of countries affected by both climate change and rising water-demand. All this justifies the current concern about the degradation of freshwater systems leading to rapid extinctions of organisms — in some cases even matching the declines recorded in tropical forests (Ricciardi and Rasmussen 1999).

There is general consensus today that some alien species will continue to be major drivers of degradation and loss of aquatic systems (Sala et al. 2000; Millennium Ecosystem Assessment 2005). The vulnerability of inland waters to bioinvasions is due to several factors (Gherardi 2007a), including the higher intrinsic dispersal ability of freshwater species compared with terrestrial organisms (Beisel 2001) and the strong impact of both human disturbance (Ross et al. 2001) and altered seasonal temperature regimes (Eaton and Scheller 1996). Species introduction into inland waters is associated with the intensity with which humans utilise these systems for recreation, food sources, and commerce (Rahel 2000), being a direct consequence of economic activity and trade globalisation that benefit millions worldwide (Lodge and Shrader-Frechette 2003). This situation has generated a conflict between two often competing goals — increasing economic activity and protecting the environment, which makes it difficult to decision-makers to develop policies aimed at containing the spread of aliens and mitigating the ecological risks they pose (Gherardi 2007a).