STATUS, PREDICTION AND PREVENTION OF INTRODUCED CORDGRASS SPARTINA SPP INVASIONS IN PACIFIC ESTUARIES, USA

Along the Pacific coast of North America, four introduced cordgrass sp ecies (Spartina alterniflora, S. anglica, S. patens and S. densiflora) have thus far invaded five isolated estuaries. Dense growth of introd uced Spartina spp. reduces open mud feeding habitats of shorebirds, wh ile in the upper intertidal, introduced Spartina spp. compete with nat ive salt mal sh vegetation. Prediction of Spartina invasions is facili tated by the remarkable restriction of these species to distinct estua rine habitats which generally lack interspecific competitors and herbi vores. We used physical characteristics to identify 31 specific sites along the US Pacific coast that are vulnerable to future Spartina inva sions and then used species characteristics, like native latitudinal r ange and past invasion success, to predict which Spartina species will be likely to invade these sites in the future. All 31 sites were pred icted to be vulnerable to S. alterniflora, while the other invasive Sp artina spp. may be restricted to a subset of the vulnerable sites. At a finer scale, within a vulnerable site, the mean tidal range can be u sed to predict the extent of spatial spread of a Spartina sp. after co lonization. These prediction techniques might be used to identify and prioritize sites for protection against future invasions. We suggest t hat a cost-effective way to prevent the transformation of unique North American Pacific mudflat and saltmarsh communities into introduced Sp artina-dominated marshes is to survey the vulnerable sites frequently and eliminate introduced Spartina spp. propagules before they spread. Copyright (C) 1996 Published by Elsevier Science Limited