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Significant alteration of both marsh composition and structure due to the establishment of invasive Spartina, and especially Spartina alterniflora and its hybrids, can be observed around the San Francisco Estuary. Over the last 35 years, introduced Spartina species have spread rapidly, both vegetatively and by seed, becoming established in numerous wetland habitats and marsh restoration sites throughout the Estuary.
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on any thumbnail for a full sized image. |
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| Impacts
to Endangered Species |
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S. patens competes for space with the federally-listed Chloropyron molle ssp. molle. |
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| S.
alterniflora/hybrids choke channels which the endangered California
Ridgway's rail uses to forage. Photo: USFWS. |
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| Spartina
patens and S. densiflora colonize middle and upper marsh,
displacing native pickleweed marsh, habitat of the endangered salt
marsh harvest mouse. Photo: USFWS. |
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| Conversion
of Tidal Mudflat to Meadow |
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Individual S. alterniflora hybrid clones coalesce to form a
cordgrass meadow. Photo: Stephen Joseph |
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S. alterniflora/hybrid clones accrete and stabilize sediment among
their dense stems, actually increasing the elevation of the mudflat
for further colonization. Alameda Island, 2001. Photo: Stephen Joseph |
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| Loss
of Shorebird Foraging Habitat |
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| Over 1 million migratory shorebirds pass through San Francisco Bay annually, feeding on the unvegetated mudflats at low tide. Loss of mudflat habitat to Spartina invasion will seriously impact shorebirds on the Pacific Flyway route. |  |
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Dunlins foraging on open mudflat in San Francisco Bay. Photo: USFWS. |
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| Loss
of Critical Channel Habitat |
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| S. alterniflora/hybrids quickly fill in the open mud of channels and sloughs, altering marsh hydrology and channel habitat. |  |
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| S. alterniflora hybrids clog Colma Creek in San Mateo County, increasing the risk of upland flooding. |  |
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| Local
Extinction of Native California Cordgrass |
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Native Spartina foliosa is threatened with local extinction as a result of hybridization with S. alterniflora. Hybrid populations are rapidly spreading throughout the San Francisco Estuary. If the hybrid population is left unchecked, it is anticipated that native Spartina foliosa could become the first naturally dominant plant species to go extinct in its own ecosystem since the passage of the Endangered Species Act of 1973. |
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| Hybrid S. alterniflora clone established in native S. foliosa marsh in Tiburon. Hybrids will easily pollinate the native cordgrass to produce more hybrid seed. |  |
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| Comparison of native S. foliosa inflorescence (on left) to hybrid S. alterniflora inflorescence. |  |
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| Failure
of Local Wetland Restoration Project Objectives |
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Colonization by introduced Spartina in newly restored marshes creates a vastly different marsh structure and composition than that of a native marsh. Therefore, efforts to recover native species and habitat will be undermined by introduced cordgrasses. Restoration of tidal action to new properties in highly infested areas of the Estuary should be postponed until exotic cordgrass is controlled. |
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S.
alterniflora hybrids (circular growth pattern on mudflat) have
colonized this 49 acre restoration site near Whale's Tail Marsh
in Hayward. |
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| Seedlings of S. alterniflora hybrids invade a newly opened marsh restoration site. |  |
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©2003 ISP info@spartina.org