SF Invasive Spartina Project
  San Francisco Estuary Invasive Spartina Project
Invasion Impacts

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.

Click on any thumbnail for a full sized image.

Impacts to Endangered Species

S. patens competes for space with the federally-listed Chloropyron molle ssp. molle.

image/_cordyl-s-patens6.jpg, 3.1K
  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
  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
  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. image/_sfskyline.jpg, 1.9K
  Dunlins foraging on open mudflat in San Francisco Bay.
Photo: USFWS.
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Loss of Critical Channel Habitat
  S. alterniflora/hybrids quickly fill in the open mud of channels and sloughs, altering marsh hydrology and channel habitat. image/_channel.jpg, 2.2K
  S. alterniflora hybrids clog Colma Creek in San Mateo County, increasing the risk of upland flooding. image/_channel-p0000518.jpg, 2K
Local Extinction of Native California Cordgrass

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.

  Hybrid S. alterniflora clone established in native S. foliosa marsh in Tiburon. Hybrids will easily pollinate the native cordgrass to produce more hybrid seed. image/_blackies-salt.jpg, 1.8K
  Comparison of native S. foliosa inflorescence (on left) to  hybrid S. alterniflora inflorescence.  image/_inflr-sfolvs-hyb-close.jpg, 2.2K
Failure of Local Wetland Restoration Project Objectives

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.


S. alterniflora hybrids (circular growth pattern on mudflat) have colonized this 49 acre restoration site near Whale's Tail Marsh in Hayward.
Photo: Stephen Joseph

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  Seedlings of S. alterniflora hybrids invade a newly opened marsh restoration site. image/_hybrid-seedlings.jpg, 2.7K

Preserving Native Wetlands

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