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.
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.
For more recent survey results, see ISP's 2007 Monitoring Report. (PDF 1.6 MB)
2004 Key Findings
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
- 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.
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.
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
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.
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).
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.
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.
Table of Contents
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)
Table of Contents
|2000-2001 Survey Key Findings
|Net Acres by Species
- 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.
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.
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.
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.
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,
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.
Bay Photo Gallery
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,
Lagoon Photo Gallery
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,
Coast Estuaries Photo Gallery
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