The problem of introduced species in management and mitigation

Abstract

One hundred years ago the striped bassMorone saxatilis was introduced in the San Francisco Bay estuarine system from the east coast of the United States. It was part of our national policy at the time to transplant all potentially useful species everywhere else. The policy was facilitated by completion of the transcontinental railroad in 1869. As a result, the present ichthyofauna of the San Francisco Bay area is largely alien. Introduction of eastern oystersCrassostrea virginica resulted in the inadvertent introduction of many species of invertebrates. Identification of these introduced species was not realized as a problem until recently, and no one knows how many exotic species there are. In other parts of the world there are examples of similar introductions, e.g.Crepidula fornicata andRhithropanopeus harrisi in Europe. Although it is now the policy to frown upon and prohibit introductions, they cannot be prevented and the process still continues, as witnessed by the examples ofElminus modestus in Europe andPalaemon macrodactylus in California. In the USA the recently developed idea of “mitigation,” the artificial replacement of disturbed or destroyed areas by development of quasi-natural areas in compensation, has been accompanied, at the hands of inexperienced practitioners, by potentially dangerous introductions of exotic species. The assumption, for example, that cordgrass(Spartina) should be equally beneficial everywhere in the world has led to the disrupting introduction of potentially hybridizing species in New Zealand and aggressive immigrants in Oregon marshes. This situation calls for more sophisticated understanding of the role of introduced species in natural aquatic ecosystems, and a higher degree of competence in systematic biology.