Biological invasions of estuaries without international shipping: the importance of intraregional transport

Increased awareness of the problem of introduced marine species has led to recent surveys of several large bays with international shipping. To our knowledge, no thorough search for introductions has been carried out in an embayment not connected to an international harbor. In 1998, we investigated the macroinvertebrate fauna of Elkhorn Slough (ES), an estuary in central California. Fieldwork and a literature review revealed 56 known exotic species at ES, a surprising diversity considering the rather modest search effort, the relatively natural setting of this estuary, and the lack of international shipping. While some exotic species at ES were probably introduced directly from distant waters with cultivated oysters, others likely arrived more indirectly via San Francisco Bay or other regional ports with thriving populations of invaders, travelling for instance as adults fouling boats or as larvae on currents. The effect of international shipping, including ballast water dumping, is thus not limited to areas with major harbors, but rather reverberates up and down the coast to seemingly isolated embayments. (C) 2001 Elsevier Science Ltd. All rights reserved.