| Summary: | Nonnative Spartina species (cordgrasses) are widely distributed along the West Coast of North America, but have not invaded all bays with susceptible habitat. We used drift cards to assess the patterns and rates of potential Spartina propagule dispersal by ocean currents from estuaries with significant populations of one or more Spartina species. Cards were released monthly for 1 yr from Willapa Bay, Washington; Humboldt Bay, California; and San Francisco Bay, California; with recovery information reported by volunteers. Recovery rates averaged 37% for all release sites. Cards were commonly recovered close to their bay of release but were repeatedly found hundreds of kilometers both north and south of their release location. Cards most generally traveled northward from the release sites. Cards from Humboldt and Willapa bays were commonly recovered along the British Columbia coast, particularly in the winter. Cards released from Humboldt Bay were found farthest from their release sites. One card from Humboldt Bay traveled 2,800 km to Kodiak Island, Alaska. The timing of seed production, combined with prevailing currents, puts bays currently uninfested by Spartina at risk of repeated propagule loading by ocean currents. A coordinated coast-wide strategy for eradication of all nonnative Spartina will be critical to the success of individual bay-wide eradication efforts.Nomenclature: Common cordgrass, Spartina anglica C. E. Hubbard, dense-flowered cordgrass, Spartina densiflora Brongn., saltmeadow cordgrass, Spartina patens (Ait.) Muhl., smooth cordgrass, Spartina alterniflora LoiselManagement Implications: Nonnative estuarine cordgrasses (Spartina spp.) are invasive weeds of saltmarshes and open mudflats in many bays and estuaries of North America, Australia, China, India, New Zealand, and numerous European countries. In North America the largest core infestations established along the Pacific Coast during the last 150 yr at Willapa Bay, Washington; Humboldt Bay, California; and San Francisco Bay, California. ...
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