Global introductions of crayfishes: Evaluating the impact of species invasions on ecosystem services.

Impacts of nonindigenous crayfishes on ecosystem services exemplify the mixture of positive and negative effects of intentionally introduced species. Global introductions for aquaculture and ornamental purposes have begun to homogenize naturally disjunct global distributions of crayfish families. Negative impacts include the loss of provisioning (e.g., reductions in ed- ible native species, reproductive interference or hybridization with native crayfishes), regulatory (e.g., lethal disease spread, increased costs to agricul- ture and water management), supporting (e.g., large changes in ecological communities), and cultural (e.g., loss of festivals celebrating native crayfish) services. Where quantification of impacts exists (e.g., Procambarus clarkii and Pacifastacus leniusculus in Europe), regulations now prohibit introduction and spread of crayfishes, indicating that losses of ecosystem services have out- weighed gains. Recent research advances such as predicting invasiveness, predicting spread, improved detection and control, and bioeconomic analy- sis to increase cost effectiveness of management could be employed to reduce future losses of ecosystem services.