Nonindigenous crayfishes threaten North American freshwater biodiversity: Lessons from Europe

North America harbors about 390 native species of crayfishes, 75% of the wo rld's total. In this article, we highlight the threats posed by nonindigeno us crayfishes to freshwater ecosystem function, fisheries, and the biodiver sity of native crayfishes; draw some lessons for North American freshwater conservation from the experience with nonindigenous crayfishes in Europe; a nd review existing regulations that address the introduction of nonindigeno us crayfishes. Most North American crayfishes have naturally small ranges i n the southeastern United States, rendering them very vulnerable to environ mental change. Ln contrast, Europe has only five, broadly distributed, nati ve crayfishes, all of which have been greatly affected by environmental cha nges, 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 populati ons of native European crayfishes and the political responses to it offer u seful guidance to efforts to protect North American freshwater biodiversity and ecosystems. As in Europe, the most important threat to native North Am erican 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 fish eries, extirpated many populations of native crayfishes, and contributed to the global extinction of at least one native crayfish species. However, mo st species are still relatively unaffected, but the smaller ranges of most North American crayfishes make them more vulnerable than European crayfishe s. Thus, a narrow window of opportunity exists to protect the function of N orth American aquatic ecosystems, their fisheries, and the unique biodivers ity of crayfishes that they contain.