ABSTRACT
In all cases, prevention is the most effective form of management (Maynard and Nowell, 2009; Hulme et al, 2009b).
Freshwater systems present an additional suite of complications for prevention and control efforts, partly for some of the reasons that freshwater ecosystems are vulnerable in the first place, as noted in Chapter 1 (see also Shine et al, 2000; Millennium Ecosystem Assessment, 2005). For example, some European freshwater invaders, such as muskrat (Ondatra zibethicus), or Chinese mitten crab (Eriocheir sinensis) are known to cause negative impacts in 20-50 regions, and overall freshwater invaders, along with terrestrial vertebrates, affect the widest range of ecosystem services of all taxonomic groups of invasive species in Europe (Vilà et al, 2010). Moreover, invasions in freshwater ecosystems often cause trophic cascades and introduced predators seem to have greater effects due to poor defence mechanisms and greater naïvety of native species towards novel predators (Cox and Lima, 2006). Prevention is difficult due to the scale of anthropogenic use of freshwater systems, which leads to high frequency, intensity and duration of introductions (e.g. Ricciardi and MacIsaac, 2000; Mack, 2003; Hulme et al, 2008; Pyšek et al, 2010). Once species are introduced, the inherent connectivity of freshwater
systems makes management problematic, as this (1) allows rapid establishment and spread; (2) often allows rapid recolonization or repopulation following treatment if water bodies are not effectively isolated from propagule sources; and (3) enhances the risk of application of (for example) chemical or biological control methods that are not species-specific or which may easily spread through the system. This chapter briefly reviews the general forms of IAS management in relation to freshwater ecosystems, drawing where appropriate on some of the observations made in the case studies presented in this volume.
