Nonindigenous Crayfishes Threaten North American Freshwater Biodiversity: Lessons from Europe

North America harbors about 390 native species of crayfishes, 75% of the world's total. In this article, we highlight the threats posed by nonindigenous crayfishes to freshwater ecosystem function, fisheries, and the biodiversity of native crayfishes; draw some lessons for North American freshwater conservation from the experience with nonindigenous crayfishes in Europe; and review existing regulations that address the introduction of nonindigenous crayfishes. Most North American crayfishes have naturally small ranges in the southeastern United States, rendering them very vulnerable to environmental change. In contrast, Europe has only five, broadly distributed, native crayfishes, all of which have been greatly affected by environmental changes, especially the introduction of nonindigenous crayfishes (mostly from North America). In response, many European governments have adopted strict regulations to protect native crayfishes. The loss of thousands of populations of native European crayfishes and the political responses to it offer useful guidance to efforts to protect North American freshwater biodiversity and ecosystems. As in Europe, the most important threat to native North American crayfish biodiversity is nonindigenous crayfishes (many from within North America). In several well-documented cases, nonindigenous crayfishes have greatly altered North American lake and stream ecosystems, harmed fisheries, extirpated many populations of native crayfishes, and contributed to the global extinction of at least one native crayfish species. However, most species are still relatively unaffected, but the smaller ranges of most North American crayfishes make them more vulnerable than European crayfishes. Thus, a narrow window of opportunity exists to protect the function of North American aquatic ecosystems, their fisheries, and the unique biodiversity of crayfishes that they contain.