San Francisco Estuary Invasive Spartina Project
  Maps and Findings
  Invasive Spartina project
Much of the shoreline survey of the San Francisco Estuary was conducted by kayak.
Spartina distribution map

ISP Maps show the distribution of invasive Spartina in the San Francisco Estuary as well as the outer estuaries of Bolinas Lagoon, Point Reyes National Seashore and Tomales Bay in various years.

The ISP surveys the Bay annually to assess and map the distribution of introduced Spartina species. The mapping project is a field-based effort, utilizing Global Positioning System (GPS) units to collect location and ecological data for each found population of invasive Spartina.  In addition to detailed field mapping, highly infested marshes are mapped by digitizing ground-truthed color IR aerial photos. Genetic testing is conducted to confirm identification of S. alterniflora hybrids.

All collected data is integrated into a Geographic Information System (GIS) for analysis, and used in planning the regionally coordinated Spartina control program.

For more information on the mapping techniques please refer to Monitoring Program Quality Assurance Document. 
(PDF, 3.3MB)

Survey Findings
San Francisco Estuary Outer Coast Estuaries

For more recent survey results, see ISP's 2007 Monitoring Report. (PDF 1.6 MB)

Photo Galleries
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San Francisco Estuary

Outer Coast Estuaries

San Francisco Estuary

2004 Key Findings

Spartina distribution map
Survey Maps

  • The distribution of introduced Spartina species throughout the San Francisco Estuary has not changed significantly since the 2001 Bay-wide inventory survey. However, the population has spread to 707 net acres, up 47% from the 2001 estimate of 482 net acres.

  • The population distribution shows that the largest populations are still near the original sites of introduction, however the outlying populations in native marsh are increasing with frequency.

  • The San Francisco Estuary Spartina invasion is a hybrid invasion. Genetic analyses indicate that the majority of the plants sampled were S. alterniflora-hybrids, rather than pure S. alterniflora.

  • The presence of S. densiflora hybrids in the Estuary have now been confirmed by Dr. Ayres and the U.C. Davis Spartina Lab. The S. densiflora hybrids have been found at Creekside Park, Corte Madera Creek, and Corte Madera Marsh Reserve in Marin County.
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One native Spartina species, S. foliosa, and four introduced Spartina species - S. alterniflora/hybrids, S. densiflora, S. anglica and S. patens - are currently found in the San Francisco Estuary.  Three of the invasive Spartina species are known to have been deliberately introduced into the bay in the 1970's as part of marsh restoration projects.  Some transplanting of the introduced species to other restoration sites probably occurred, however, the majority of the population occurs as a result of natural spread, both by underground tiller growth and by seed dispersal.

Spartina alterniflora and its hybrids (S. alterniflora x S. foliosa) are the most widespread invasive Spartina species in the Estuary, totaling 727 net acres spread over six counties (2004).  S. alterniflora is native to the east coast and was introduced to San Francisco Bay as part of an experimental marsh restoration project along the Alameda flood control channel in Hayward in the early 1970's.  S. alterniflora readily hybridizes with and out-competes the native California cordgrass, S. foliosa, and threatens this native cordgrass with local extinction.  See maps for current S. alterniflora/hybrid distribution.

Spartina anglica and S. densiflora were introduced to the San Francisco Estuary in 1976, as part of a marsh restoration project adjacent to Corte Madera Creek in Marin County.  S. anglica, itself a hybrid of S. alterniflora and England's S. maritima,  was likely transplanted  from Puget Sound in Washington State, where it was introduced in the 1960's.  S. densiflora, native to Chile, was transplanted here from Humboldt Bay, CA, where it has been established since the nineteenth century lumber trade between the two locations.

S. densiflora has now spread beyond the original marsh plantings to the entire two mile length of Corte Madera Creek and is spreading beyond the creek into San Francisco Bay. See maps for current S. densiflora distribution. The northern-most population is found at Brickyard Cove in San Rafael on the West Bay and Point Pinole on the east side of the Bay. An outlying population in the South Bay is found at Sanchez Marsh in Burlingame Lagoon.

In 2004, a S. densiflora-foliosa hybrid was found at Creekside Park and Corte Madera Creek in Marin County (D. Ayres, unpublished data).

S. anglica, considered the most invasive Spartina species in the world, is currently contained within its original planting site, but is spreading within the marsh and threatens to invade Corte Madera Creek.

S. patens, also native to the east coast, occurs at one known location in the Benicia State Recreation Area.  The dense tussocks are steadily spreading in the higher marsh habitat, displacing native plant species such as the endangered soft bird's beak (Cordylanthus mollissp. mollis) and pickleweed (Salicornia spp.), habitat of the endangered salt marsh harvest mouse (Reithrodontomys raviventris). The introduction history of this population of S. patens is unknown.

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2004 Invasive Spartina Distribution

The 2004 survey revealed that hybrid swarms ( S. alterniflora X S. foliosa) have rapidly spread in the South, Central and North Bay regions. Hybrids are more vigorous and reproductively fit than either of the parents. S. alterniflora and its hybrids have established as far north as San Rafael in Marin County, and to Point Pinole in Contra Costa County. Populations are sparse north of the San Francisco Bay Bridge, and south of the Dumbarton Bridge, but appear to be spreading along the shoreline. The densest populations are in the Central Bay, nearest the sites of original introduction. Many creeks are now infested.  S. densiflora has spread from its original introduction on Corte Madera Creek in Marin County as far north as Pt. San Pedro, with one individual confirmed as far north as Dutchman Slough in Solano County.  A separate population of S. densiflora is located at Pt. Pinole.  S. anglica occurs in a single marsh on Corte Madera Creek, but appears to be spreading into the creek. S. patens occurs at Southampton Marsh at Benicia State Recreation Area, but unconfirmed sightings have been reported near Tubbs Island in Sonoma County.  (See maps for locations)

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2000-2001 Survey Key Findings
Spartina distribution map
Net Acres by Species Region Map Survey Maps
  • The distribution of introduced Spartina species throughout the San Francisco Estuary is more widespread than previously known. Populations of one or more species are now established in each of the South, Central, North and Suisun Bay subregions.

  • Although widespread, the population distribution shows that the largest populations are still near the original sites of introduction with decreasing frequency of outlying populations over distance.

  • Populations appear to begin at the Bay and slough edges and move into the interior of marshes as the invasion progresses.

  • 75% of the hybrid population is located in the South Bay subregion north of the Dumbarton Bridge.

  • The majority of creeks flowing into the Central Bay subregion are invaded.

  • Results of DNA tests (UC Davis Spartina Lab) of S. alterniflora/hybrid plants collected for this survey suggest that it is S. alterniflora x S. foliosa hybrids rather than S. alterniflora x S. foliosa hybrids rather than S. alterniflora that are rapidly colonizing the Estuary.
Outer Coast Estuaries

All California estuaries are considered threatened by invasive Spartina species.  Seeds can travel long distances on the tides or with migrating birds, and can be accidentally transported between estuaries on kayaks, boots, field equipment, or with aquaculture and restoration activities.  The mode of introduction of these new invasive Spartina populations to these outer coast estuaries is unknown. In the last months of 2001, invasive Spartina populations were found in Tomales Bay, Bolinas Lagoon, and Drakes Estero on the outer California coast. Over the course of 2002, Tomales Bay, Point Reyes National Seashore and Bolinas Lagoon were surveyed by local biologists, landowners and managers and all known populations of non-native Spartina were controlled. In 2003 to 2005 outer coast sites determined to be at risk of invasion were re-surveyed, and known sites were monitored for new-found populations. New populations were found at Marshall Cove (2003-5), Tom's Point (2004-5) and Tomasini Point (2005). All new-found plants were eradicated.

In January of 2003, an additional clone of non-native Spartina was found in the southern end of the Bolinas Lagoon. The ISP currently worked with local biologists and land managers to plan for the treatment of this plant. The chosen treatment was covering with geotextile fabric. The treatment was successful and the cover removed November 2005.

The ISP continues to work with local biologists, stakeholders and land managers and to monitor for the presence non-native Spartina in the outer coast marshes.

Tomales Bay
Following up on several S. densiflora plants believed eradicated from Marshall Cove in 1999, in October 2001 ISP staff found a population of 4 mature and approximately 60 seedlings of S. densiflora at this same location.  A comprehensive survey of Tomales Bay was quickly organized by ISP with the cooperation of many local biologists and landowners.  Two additional populations of Spartina densiflora have been found to date at Tomasini Point and at Tom's Point. See map: (PDF, 431K) (JPG, 148K) In 2004 and 2005, 17 more plants were found at Marshall Cove and again manually removed with shovels. All S. densiflora plants found in Tomales Bay have been shovelled up and the plant material carried out of the area.

Tomales Bay Photo Gallery››

Bolinas Lagoon
In November, 2001, a single S. alterniflora clone was discovered in Bolinas Lagoon by a local biologist.  A quick survey of the lagoon was organized, and no other invasive Spartina was found. The vector for this introduction is unknown.  The landowner took responsibility for manually removing this plant and conducting ongoing surveys of the control area. In January 2003 an additional clone was found at the south end of the lagoon. ISP worked with the landowner to arrange for the treatment of this plant. This plant was covered with geotextile fabric in 2004, was determined dead and uncovered in fall 2005. See map: (PDF, 455K)

Bolinas Lagoon Photo Gallery››

Drakes Estero
In December of 2001, a single S. alterniflora plant was found in Drakes Estero at Point Reyes National Seashore.  A visitor hiking in the area noticed an unusual plant, worried it may be invasive Arundo donax or bamboo, and reported it to park staff.  Park biologists and lab tests confirmed the plant is S. alterniflora.  A full survey of the estero took place and a total of five non-native Spartina clones were found. In the summer of 2002, all five clones were covered with geo-textile fabric. A summer 2003 survey took place and found a sixth plant that was covered immediately. In 2004-5, the plants were uncovered. See map: (PDF, 465K)

Outer Coast Estuaries Photo Gallery››

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