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Snakeheads continued on page 40
Volume 4 No. 4 February 2002
DIGEST
Providing current information on monitoring and controlling the spread of harmful nonindigenous species.
ANS
Aquatic Nuisance Species
In This Issue:
I
nvasive species often exhibit resistant characteristics. Even the
extreme ecological conditions of tidal salt marshes, high
salinity, and anoxic soils, do not exclude invasive species. The
inter-tidal, salt marsh habitats of San Francisco Bay were invaded
by a non-indigenous smooth cordgrass,
Spartina alterniflora, which
was intentionally introduced from the Atlantic seaboard for erosion
control in the early 1970s (Callaway and Josselyn 1992). This
invader hybridized with native California cordgrass,
Spartina
foliosa,
and produced hybrid swarms that can potentially spread
down the inter-tidal gradient and cover the naturally open mud
(Ayres et al, 1999).
The salt marshes and inter-tidal areas of San Francisco Bay are
invaluable. Only a small fraction of the original extent of this
habitat remains. Most has been diked, drained, and filled over the
last century (Macdonald 1977). The remaining salt marshes of San
Francisco Bay are home to valuable native species, including two
federally listed endangered animal species, the salt marsh harvest
New Zealand Mud Snail Invades
Western United States. . . . . . . . . . 42
ANS Update. . . . . . . . . . . . . . . . . 45
San Francisco Bay and Beyond:
Invasive Spartina Continues to Spread
Among Pacific Estuaries. . . . . . . . 46
Upcoming Conferences
and Meetings . . . . . . . . . . . . . . . . 47
S
nakeheads (Family Channidae) have
long been recognized as a potentially
problematic species if introduced and
established in U.S. waters. In fact, Texas
prohibited some or all species in this family
as far back as the mid 1960s (Howells
1999). Since then, at least a dozen other
states have added snakeheads to their
prohibited species list. Original concerns
focused on periodic importation by the
aquarium trade and fear of release;
however, recent shipments of living fish to
seafood markets have highlighted an
entirely new area of concern.
Also called serpent-headed fish,
snakeheads are elongated, torpedo-shaped
fish from tropical Africa and southern Asia
(Nelson 1994). The name snakehead comes
from the presence of large scales on the
head, reminiscent of the large epidermal
scales or cephalic plates on the heads of
snakes, and the forward placement of the
eyes on the head. Snakeheads have long
dorsal and anal fins as well as rounded
caudal fins and resemble the bowfin,
Amia
calva
. Snakeheads vary in size, with one or
two species reaching only about six inches
in length as adults, but others may exceed
four feet and weigh more than 44 pounds
By Robert G. Howells, James D. Williams, and Walter R. Courtenay, Jr.
By Debra R. Ayres and Donald R. Strong
Spartina
continued on page 38
Figure 1. Spartina alterniflora in San Francisco Bay
SnakSnakeheads Repreheads Represent anesent an
IncrIncreasing easing ThrThreat to Ueat to U.S. .S. WWatersaters
The Spartina InThe Spartina Invvasion of San Francisco Bayasion of San Francisco Bay
FRESHWATER SOCIETY
February 2002 Volume 4, No. 4
38
Aquatic Nuisance Species Digest
Aquatic Nuisance Species Digest
Freshwater Society Staff
Jeanne C. Prok, Managing Editor
Gene B. Hansley, Editorial Consultant
Editorial Board
Lars W. J. Anderson, Ph.D.
University of California–Davis
James T. Carlton, Ph.D.
Williams College–Mystic Seaport
John F. Christmas
Maryland Department of Natural Resources
William Culpepper
SePRO Corporation
Thomas Fritts, Ph.D.
USGS–Biological Resources Division
Katherine Glassner-Shwayder
Great Lakes Commission
Douglas A. Jensen
University of Minnesota Sea Grant
John Kahabka
New York Power Authority
Stuart C. Leon, Ph.D.
U.S. Fish and Wildlife Service
Leo G. Nico, Ph.D.
USGS–Biological Resources Division
Jay Rendall
Minnesota Department of Natural Resources
William E. Roper, Ph.D.
U.S. Army Corps of Engineers
Joe Starinchak
U.S. Fish and Wildlife Service
Edwin Theriot, Ph.D.
U.S. Army Corps of Engineers
Janet Thompson
USGS–Water Resources Division
S. Kim Webb
U.S. Fish and Wildlife Service
Randy Westbrooks, Ph.D.
U.S. Department of Agriculture
Direct questions and comments about ANS Digest
to: Jeanne Prok, Freshwater Society, Gray
Freshwater Center, 2500 Shadywood Road,
Excelsior, MN 55331; (888) 471-9773;
e-mail: Jeanne@freshwater.org.
Aquatic Nuisance Species Digest (ISSN 1083-864) is
produced by the Freshwater Society, a public non-
profit organization whose mission is to pursue the
sustainable use of freshwater resources through edu-
cation, conferences, and publications. Funding for
this issue of ANS Digest came from the United
States Department of the Interior, Fish and Wildlife
Service. The U.S. Fish and Wildlife Service and the
National Oceanic and Atmospheric Administration
(NOAA) co-chair the Aquatic Nuisance Species Task
Force, an intergovernmental organization dedicated
to preventing and controlling aquatic nuisance
species, and implementing the Nonindigenous
Aquatic Nuisance Prevention and Control Act
(NANPCA) of 1990.
© 2002, Freshwater Society.
Spartina continued on next page
Spartina continued from page 37
Task
ANS
Force
U. S .
FISH & WILDLIFE
SERVICE
D
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A
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T
M
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N
T
O
F
T
H
E
I
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T
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O
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mouse, Reithrodontomys raviventri, the California clapper rail, Rallus longirostris
obsoletus
, and the federally listed endangered plant, soft bird’s beak, Cordylanthus mollis
mollis
. These salt marshes support fisheries and recreation, and serve essential ecosystem
functions such as flood control. The open mud of San Francisco Bay is the primary habitat
of one of four Audubon Society
“Hemispheric Reserves” for
shorebirds. California
cordgrass,
Spartina
foliosa
, forms
a natural
lower
boundary to
salt marsh
vegetation and
provides essential habitat
for a variety of native
vertebrates and invertebrates, making the plant
an essential component of natural California salt marshes.
Spartina foliosa is a short
cordgrass that grows sparsely, rarely attaining height greater than 75 cm. It is restricted to
high elevations on the inter-tidal plane, and does not grow lower than the average high
water level. This characteristic leaves mud areas open in Pacific estuaries. Other native
cordgrasses do not exist on the Pacific coast. The range of
Spartina foliosa extends from
Bodega Bay, 100 km north of San Francisco, into Baja California, Mexico. Thus, biotic
threats to the salt marsh habitats of San Francisco Bay could readily spread southward, even
into Baja California.
The original control efforts with invasive smooth cordgrass,
S. alterniflora, in San
Francisco Bay centered upon ecological competition with native California cordgrass,
S.
foliosa
(Callaway and Josselyn, 1992). What was thought to be invasive smooth cordgrass,
initiated growth earlier in the spring, had grown 10-fold the above-ground and 2-fold the
below-ground annual biomass, grew as much as 60 cm taller, and spread laterally 1.5 times
faster than the native. In a field competition experiment, 75% of cleared patches were re-
colonized by what was inferred by these authors to be pure smooth cordgrass. The invader
produced more flowers and set more seed, and its seeds had higher germination than the
native. Finally, what was believed to be pure smooth cordgrass grew as high or higher in
the marsh, and from 9-20 cm lower, than the native, suggesting a lack of refuge in San
Francisco Bay for California cordgrass from competition with this aggressive exotic
species. After further studies, the majority, if not all, of the plants considered to be pure
smooth cordgrass in this pioneering work, turned out to be hybrids between the invading
S.
alterniflora
and the native S. foliosa.
Recent studies suggest that hybrids between native California cordgrass and the
invasive smooth cordgrass are probably the most menacing of the more than 200 known
non-indigenous species in this “world’s most invaded estuary” (Cohen and Carlton, 1998).
If left uncontrolled, this invasion has the potential to convert the salt marshes and open mud
of San Francisco Bay into vast stands of hybrid and invader cordgrass, which will
accumulate sediment, elevating the marsh. The probable ecological outcome can be seen
from the results of the spread of hybrid
S. anglica in England 100 years ago. After
hybridization and chromosome doubling led to the formation of
S. anglica, this hybrid was
sufficiently vigorous to displace the native European cordgrass in the English marshes and
even the introduced
S. alterniflora parent. As S. anglica spread, the numbers of wading
birds were reduced in invaded marshes; these birds feed upon open mud but not within
S.
angelica
(Goss-Custard et al. 1995). Rapid sediment accretion elevated English marshes
by as much as four cm/year and periodic dieback silted navigation channels (Ranwell
1964). Today, dense stands of
S. anglica remain in some English estuaries changing
navigational routes and estuary flow patterns (Raybould 1999).
Without control, the invader
and hybrids will spread from south
San Francisco Bay northward to
threaten the North Bay and the
Sacramento River estuary.
Aquatic Nuisance Species Digest
February 2002 Volume 4, No. 4
39
Using nuclear DNA markers, genes of the invader S.
alterniflora
have been found to spread rapidly through San
Francisco Bay cordgrasses (Ayres et al. 1999). Already, California
cordgrass is very rare in three marshes where alien smooth
cordgrass and/or hybrids were deliberately planted. In these three
sites, inter-specific hybrids and smooth cordgrass now grow in
high densities. Recently opened salt ponds in the area, such as
Cogswell marsh in Hayward, CA, are vulnerable to colonization
by hybrid seed.
Through a combination of nuclear DNA analysis, field
observations on flowering, and repeated attempts to cross the two
species, researchers have discovered that the formation of an inter-
specific F1 hybrid is an extremely rare event. However, crossing
between hybrids and
S. foliosa readily occurs. Research leaders
have concluded that the sweep of invader genes through native
cordgrass populations is driven by hybrids. Thus, spread of hybrids
to other marshes in California could be more immediately
threatening to the native species than introductions of
S.
alterniflora
itsel
f
With chloroplast DNA (cpDNA) researchers have studied
patterns of maternity in hybrid cordgrass (Anttila et al, 2000).
CpDNA is maternally inherited, providing information on the seed-
parents of hybrids.
S. foliosa had but a single chloroplast
haplotype, and this was unique to California cordgrass.
S.
alterniflora
from the native range along the Atlantic coast of North
America had three chloroplast haplotypes. The most significant
findings of the study were that hybridization between
S. alterniflora
and S. foliosa in San Francisco Bay has proceeded in both
directions. The majority, 26 of the 36, of hybrids contained the
S.
foliosa
cpDNA haplotype , indicating that in the majority of
instances, the seed parent of the hybrids was native California
cordgrass. Nine of the hybrids analyzed contained cpDNA
haplotypes of the invading
S. alterniflora, which indicates that the
alien is not immune from hybridization itself.
Researchers have found that some genotypes of hybrid
cordgrass grow more rapidly and ultimately taller than either
parental species. This vigorous morphology has particular
significance for growth in the salt marsh habitat. A reasonable
hypothesis is that taller plants can survive and flourish at greater
depths on the inter-tidal plane, consistent with the difference in
height and growth between the two parental species. Tidal
submergence time controls the distribution of cordgrasses on the
inter-tidal plane;
S. alterniflora in Long Island extends over 1m
farther down the tidal plane than
S. foliosa in San Francisco Bay
(Hinde, 1954). Thus, hybridization could create genotypes that
encroach upon the open mud of Pacific estuaries even farther or
more rapidly than the alien species alone.
Invasion by
S. alterniflora and hybrids is a dynamic process
that raises the inter-tidal plane by means of the accretion of
sediment within the densely packed canes of the invader and
hybrids. This means that the total area of the encroachment will be
even greater than if there was no feedback between elevation of the
site and occupation by alien and hybrid cordgrass. Robust hybrids
are predicted to overgrow native cordgrass, as discovered in the
work of Callaway and Josselyn (1992 ). A further prediction is that
the hybrids will even out-compete
S. alterniflora in areas of co-
occurrence. From ecological competition alone, the eventual result
could be the elimination by hybrids of the invader itself as well as
the elimination of native cordgrass. Growing far down onto the
mudflat, hybrid cordgrass, strengthened by genetic contributions
from both parents, may be the final successor of Bay marshes,
replacing primarily open inter-tidal mud flat habitats with dense
populations of hybrid cordgrass. Ecosystem impacts to the San
Francisco Bay estuary and beyond will be devastating.
Cordgrasses disperse primarily by seeds that float on the tide
(Daehler and Strong 1994). Seeds are set in late summer and fall
and germinate in late winter and spring on the mud of the inter-tidal
plane. Seedlings are usually scarce, and by the second year of
growth, the characteristic circular clone of stems can be seen
spreading outward from the initial position of the single seedling
tiller.
Without control, the invader and hybrids will spread from south
San Francisco Bay northward to threaten the North Bay and the
Sacramento River estuary. Hybrid seeds will float from the Golden
Gate and ultimately find their way into estuaries at Bolinas, Drakes
Estero, Tomales Bay, and Bodega Bay, CA (Daehler and Strong
1996). Similar dispersal has already occurred from the invasion of
smooth cordgrass in Willapa Bay, WA to the north (K. Sayce,
personal communication). Absent control, native ovules would be
swamped by hybrid pollen, producing hybrid swarms that
overwhelm each marsh in succession leading to the extinction of
S.
foliosa
and the transformation of the native ecosystem.
Dr. Debra R. Ayres is a post-doctoral research associate in the
Evolution and Ecology Department at the University of
California, Davis, CA.
Dr. Donald R. Strong is a Professor in the Evolution and
Ecology Department at University of California, Davis, CA.
Literature Cited:
Anttila, C. K., A. R. King, C. Ferris, D. R. Ayres, D. R. Strong. 2000. Reciprocal hybrid
formation of Spartina in San Francisco Bay. Molecular Ecology 9: 765-771.
Ayres, D. R., D. Garcia-Rossi, H. G. Davis, and D. R. Strong. 1999. Extent and degree of
hybridization between exotic (Spartina alterniflora) and native (S. foliosa) cordgrass
(Poaceae) in California, USA determined by random amplified polymorphic DNA
(RAPDs). Molecular Ecology 8: 1179-1186.
Callaway, J. C. and M. N. Josselyn. 1992. The introduction and spread of smooth cordgrass
(Spartina alterniflora) in South San Francisco Bay. Estuaries 15: 218-226.
Cohen, A. N. and J. T. Carlton. 1998. Accelerating invasion rate in a highly invaed estuary.
Science 279: 555-558.
Daehler, C. C. and D. R. Strong. 1994. Variable reproductive output among clones of
Spartina alterniflora (Poaceae) invading San Francisco Bay, California: the influence of
herbivory, pollination, and establishment site. American Journal of Botany 81: 307-313.
Daehler, C. C. and D. R. Strong. 1996. Status, prediction and prevention of introduced
cordgrass Spartina spp. Invasions in Pacific estuaries, USA. Biological Conservation 78:
51-58.
Goss-Custard, J. D., R. T. Clarke, S. V. Dit Durell, R. W. Caldow, and B. J. Ens. 1995.
Population consequences of winter habitat loss in a migratory shorebird. II. Model
predictions. Journal of Applied Ecology 32: 337-351.
Hinde, H. P. 1954. Salt marsh phanerogams in relation to tide levels. Ecological
Monographs 24: 209-225.
Macdonald, K. B. 1977. Coastal Salt Marsh. In M. G. Barbour and J. Major, eds,
Terrestrial Vegetation in California, N. Y. Wiley.
Ranwell, D. S. 1964. Spartina salt marshes in southern England. Journal of Ecology 49:
325-374.
Raybould, A.F. 1999. Hydrographical, ecological, and evolutionary change associated with
Spartina anglica in Poole Harbor. In: (ed. Sherwood B) British Saltmarshes:
Geomorphology, Biodiversity and Restoration. The Linnean Society.
Spartina continued from previous page
Aquatic Nuisance Species Digest
February 2002 Volume 4, No. 4
46
F
our nonnative species of Spartina, or cordgrass, are
quietly spreading in San Francisco Bay;
Spartina
alterniflora
and its hybrids with the native S. foliosa (see
page 37 Ayres & Strong article),
S. anglica, S. densiflora,
and
S. patens. Each of these cordgrass species is a highly
aggressive invader capable of inducing physical and bio-
logical alteration of Pacific coastal habitats in California,
Oregon, and Washington. (Daehler and Strong 1996). At
least three of these four species were introduced intention-
ally to the San Francisco Estuary to revegetate wetland
restoration sites in the 1970’s.
In 2000, the California State Coastal Conservancy
formed the San Francisco Estuary Invasive
Spartina
Project (ISP) in response to a growing need for a regional-
ly coordinated cordgrass control effort in San Francisco
Bay. An extensive ground-based survey conducted by ISP
in 2001 found that combined, nonnative
Spartina species
have expanded to nearly five hundred net acres over a peri-
od of twenty-five years. Ninety-seven percent of the popu-
lation is
S. alterniflora or hybrid. The invasion has spread
into seven Bay Area counties with some outlying popula-
tions of
S. alterniflora and hybrids established as far as
forty miles north of the original plantings. It appears that
S. alterniflora x foliosa hybrids, in particular, may be
poised to aggressively spread into Suisun Bay and possibly
upstream into the lower Sacramento River Delta. During the survey,
biologists observed that
S. alterniflora and hybrids establish lower
in elevation on the inter-tidal plane than any other native plant
species, are choking creeks, tidal sloughs, and flood control chan-
nels, and are rapidly colonizing many tidal wetland restoration pro-
jects. In heavily infested areas there is significant loss of native
species such as pickleweed
(Salicornia) and Spartina foliosa (native
California cordgrass).
S. patens was observed to be directly
encroaching on the federally and state endangered soft bird’s beak
(
Cordylanthus mollis) in one location.
The San Francisco Estuary, the largest estuary in North
America, opens into the Pacific Ocean at the famous Golden Gate.
Beyond the Golden Gate, north along the coast, are the smaller pris-
tine estuaries of Drakes Estero and Tomales Bay in the Pt. Reyes
National Seashore, Bolinas Lagoon, and Bodega Bay - all part of
the Gulf of the Farallones National Marine Sanctuary. Bolinas
Lagoon is the only designated Wetland of International Importance
(Ramsar Site) within California, Oregon, and Washington. Tomales
Bay is currently proposed for such designation. The concern has
been that
Spartina seeds might travel out the Golden Gate with the
currents and invade these outer coast estuaries. Prior to October of
2001, each of these important estuaries was believed to be free of
invasive
Spartina.
A Rapid Response Plan
In October 2001, while conducting routine follow-up on local
Spartina invasions, ISP found a population of S. densiflora, origi-
nally composed of three plants and believed eradicated in 1999 from
Tomales Bay, had
re-established and
spread. Several
mature plants and
more than 60
seedlings were
growing at the
same site, unbe-
knownst to the
landowner.
Encouraged by the
landowner’s interest
in identifying and
eradicating the
plants, ISP quickly
decided to expand
its geographic scope to include
Tomales Bay, and organized a
Spartina species identification
workshop for local Tomales
Bay biologists, private
landowners, and
open space man-
agers for the
following
week.
At the
work-
shop’s
conclu-
sion,
attendees
each agreed to
survey a sec-
tion of shoreline for invasive
Spartina and report findings to ISP.
ISP agreed to conduct a portion of the surveys, assist in surveys
where needed, coordinate necessary lab tests, and act as central
clearinghouse for all collected data. Within three weeks, the bay
had been surveyed, two additional populations of
Spartina densiflo-
ra
found, and all known populations dug out with a shovel and
removed from the area. Ongoing monitoring is planned. The cost
for this entire effort of early detection, survey and control was virtu-
ally zero due to volunteer efforts and ISP providing expertise, train-
ing, and equipment. The incredible interest and response from the
local community were essential components to this early detection
success story.
San Francisco Bay and Beyond:
San Francisco Bay continued on next page
Figure 1. Pacific Coast Estuaries Invaded
by Non-native Spartina (2001)
By Debra Smith, Shannon Klohr, Katy Zaremba
San Francisco Estuary Invasive Spartina Project
California State Coastal Conservancy, Oakland, CA
Invasive Spartina Continues to Spread Among
Aquatic Nuisance Species Digest
February 2002 Volume 4, No. 4
47
February 2002 Volume 4, No. 4
San Francisco Bay continued from previous page
Upcoming ANS Meetings and Events
National Invasive Weeds
Awareness Week 2002 (NIWAW III)
Date: February 25 - March 1, 2002
Location: Washington, DC
Contact: Rita Trostel
Phone: (970) 498-5767
4th Annual Southeast Exotic Pest
Plant Council Symposium
Date: April 3-5, 2002
Location: Renaissance Hotel, Nashville, Tennessee
Hosted by: Tennessee Exotic Pest Plant Council
Contact: Brian Bowen
Phone: (615) 532-0436
E-mail: nighttrain0@home.com
6th Meeting of the Convention on Biological Diversity
(CBD) Conference of the Parties
Date: April 8-26, 2002
Location: The Hague, Netherlands
Contact: CBD Secretariat
E-mail: www.biodiversity.org
Evolutionary Consequences of Invasions by Exotic Species
Date: April 12-13, 2002
Location: Minneapolis, Minnesota
Hosted by: University of Minnesota’s College of Biological
Sciences
For more information:
www.ima.umn.edu/geoscience/spring/bio_invasion
2002 Invasive Species Symposium
Date: June 18-19, 2002
Location: Freeborn Hall, University of California-Davis,
Davis, California
Phone: (530) 757-3331
Fax: (530) 757-7943
E-mail: events@ucdavis.edu
European Weed Research Society, 12th International
Symposium on Aquatic Weeds
Date: June 24-27, 2002
Location: Papendal National Sports Centre, Papendallaan 3,
Arnhem, The Netherlands
Phone: +31 26 370 8389
Fax: +31 26 370 6896
E-mail: ewrs.w2002@hetnet.nl
Send meeting announcements to:
Jeanne Prok, ANS Digest
2500 Shadywood Rd., Excelsior, MN 55331
e-mail: Jeanne@freshwater.org
Deadline for the next issue is May 1, 2002.
The More You Look, the More You Find
In November of 2001, a biologist who had attended ISP’s
Spartina species identification workshop found a single Spartina
alterniflora
plant in Bolinas Lagoon while kayaking. In December,
a concerned hiker in Pt. Reyes National Seashore reported a strange
plant in Drake’s Estero. Aware of the threat of Spartina, park biolo-
gists acted quickly to obtain genetic tests that confirmed this was
Spartina alterniflora. Each of these plants appears to be several
years old. Both of these estuaries were assumed free of invasive
Spartina. Suddenly all such assumptions seem dangerously sus-
pect. Vectors for these new invasions are not clear. Floating seed,
aquaculture, and recreational activities between estuaries are all
possible means of introduction. Clearly, all Pacific Coast estuaries
need to be surveyed methodically for invasive
Spartina. Early
detection is critical for a successful and cost-efficient prevention
and control program.
Surprise
Spartina findings are not limited to California. In
Washington, a wildlife technician conducting a noxious weed sur-
vey discovered a tenth of an acre patch of
Spartina densiflora in
Gray’s Harbor in December, 2001. This was the first sighting of
this species in the state of Washington. Scientists are in the process
of identifying another cordgrass sample from north Puget Sound
believed also to be
Spartina densiflora. These continued and unex-
pected
Spartina findings in well-studied estuaries further underscore
the need for comprehensive surveys of all Pacific Coast estuaries.
The Pacific Coast Spartina Invasion:
A Bird’s Eye View
Thirty-one estuaries along the Pacific Coast have been identi-
fied as vulnerable to invasion by introduced species of
Spartina
(Daehler and Strong 1996). In 2001, five new introductions were
detected on the Pacific coast including three in previously uninvad-
ed estuaries. Currently, a total of nine have at least one species of
introduced cordgrass. It is critical that vulnerable estuaries be com-
prehensively surveyed and a rapid response initiated to control any
detected populations.
Sharon Klohr, San Francisco Estuary Invasive Spartina Project
California State Coastal Conservancy
Contact: S. Klohr; sklohr@scc.ca.gov
Phone: (510) 526-4628
Literature Cited:
Pickart, A. 2001. The Distribution of Spartina densiflora and two rare salt marsh plants in
Humboldt Bay 1998-1999. USFWS report.
Daehler, C. C., and D. R. Strong. 1996. Status, prediction and prevention of introduced
cordgrass
Spartina spp. Invasions in Pacific estuaries, USA. Biological Conservation
78: 51-58.
Pacific Estuaries
... It usually grows on intertidal zone and estuary from the upper level of middle tide to low level of high tide level (Vinther et al., 2001 ). Because it plays an important role in protecting beach, change soil salinity, expanding land, and etc. S. alterniflora has been introduced to many place of the world, such as, west coast of North American, Europe, New Zealand and China (Ayres and Strong, 2002). And then, it rapidly expanded to the whole coastal zone wetlands area and became a dominant species of salt marsh vegetation. ...
... It is hard to extract S. alterniflora distribution information from image only based on spectral features. From the previous study and S. alterniflora inhabited characteristics (or ecological niche), S. alterniflora mainly distributed on intertidal zone and estuary (Ayres and Strong, 2002; Daehler and Strong, 1996; Vinther et al., 2001; Yuan et al., 2009), as shown in Fig. 3 . Intertidal zone is the potential area for S. alterniflora habitat . ...
Article
Spartina alterniflora is one of exotic plants along the coastal region in China. It was introduced as an important engineering approach to ecological restoration in the later 1970s. However, owing to its good adaptability and strong reproductive capacity, the introduced species is explosively spreading along the coastal region quickly and resulting in a significant impact on the health and safety of coastal wetland ecosystems. It is imperative to quantify the spatial extent and the rate of S. alterniflora sprawl in order to assess its ecological damages and economic impacts. Remote sensing techniques have been used to address these challenges but large unsuccessful due to mixed spectral properties. In this study, a hybrid method was proposed for S. alterniflora detection using medium resolution remote sensing images by integrating both spatial and spectral features of S. alterniflora. The hybrid method consists of two phases: (1) delineation of intertidal zone as the potential area of S. alterniflora distribution and (2) extraction of S. alterniflora fraction distribution with a mixture pixel analysis. The proposed method was tested at the Xiangshan Bay on the east coastal region of Zhejiang Province, China, and mapped the spatial extent of S. alterniflora with Landsat datasets in the 2003, 2009 and 2014. The results showed that, the S. alterniflora has grown exponentially over past 10 years. In 2003, the total area of S. alterniflora was about 590 hm(2), but quickly reached to 1 745 hm(2) in 2009, and 5 715 hm(2) in 2014. With a rate of approximately 10-folds growth within a decade, the invasive species almost occupied all muddy beaches to become the most dominant coastal salt vegetation in this region. It is believed that the strong biological reproductive capacity was the primary reason for such quick spread and at the same time human reclamation activities were also believed to have facilitated the environmental conditions for S. alterniflora sprawl.
... S. alterniflora is a perennial herb that is native to the west coast of the Atlantic and the Gulf of Mexico. It plays an important role in protecting coastal wetlands from wave erosion because of its rapid spread and great ability to promote silt deposition (Ayres et al., 2002). Therefore, S. alterniflora was successfully introduced in Yancheng coastal wetlands in the 1980s. ...
... Spartina spp. has been introduced into several countries for stabilization of embankments and coastlines (Hubbard and Partridge, 1981;Chung, 1993;Ayres and Strong, 2002). The dense underground root and rhizome networks of S. anglica can have a negative influence on biodiversity of tidal flats and other wetlands (Marks and Truscott, 1985;Xiao et al., 2016), and establishment of the species can lead to significant changes in habitat conditions (Ehrenfeld, 2003). ...
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Spartina anglica is an invasive perennial marsh grass causing significant negative impacts on tidal flat ecosystem. There have been only a few studies focusing on the patch structure of S. anglica according to size and its effects on macrofauna. A field experiment was conducted to identify effects of S. anglica patches where they have been introduced no later than 5 years after invasion occurred on macrofauna assemblages. The survey area was divided into two sections according to vegetation: (1) Suaeda japonica vegetation from 0 to 60 m away from the embankment, and (2) bare mudflat from 60 to 90 m away from the embankment. The patch sizes of S. anglica were categorized into small (1–4 m ² ), medium (5–11 m ² ), and large (13–40 m ² ) in area with four replicates for each section. The biomass ratio of the belowground and aboveground in the small size patch of S. anglica was significantly higher than those in the medium and large size patch of S. anglica . It indicated that more resource was allocated to rhizomes in small size patch with short invasion history (1 ~ 2 years). After S. anglica invaded, macrofauna richness (70%), Shannon-Wiener diversity (80%), and density (67%) were decreased. However, infaunal deposit-feeding polychaete Perinereis linea and epifaunal gastropods Batillaria cumingi and Lactiforis takii increased by S. anglica . Ordination of macroinvertebrate assemblages separated the habitat with S. anglica invasion from the adjacent uninvaded tidal flat and Suaeda japonica habitats. This study offers a significant insight into early invasion strategies of an aggressive plant invader, S. anglica for management of coastal wetlands and its impacts on macrofaunal assemblages.
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1. This paper models empirically how habitat loss in winter might affect the size of the European population of oystercatchers Haematopus ostralegus ostralegus. It explores how a density-dependent mortality rate in winter interacts with a density-dependent production rate in summer to determine the total, year-round population size following a loss of winter habitat which itself leads to intensified competition for food and hence increased winter mortality rates. 2. Simulations over a range of probable parameter values show that the density at which winter mortality becomes density-dependent, cW, simply determines the point at which population size is affected as habitat is gradually removed. The population is affected sooner in the more widely fluctuating Continental sub-populations than in the less variable Atlantic subpopulations. 3. Once winter density reaches cW, the consequences depend on the slope, bW, of the density-dependent winter mortality function. In all subpopulations, the reduction in population size increases sharply as bW increases, but only at low values; above a certain level, further increases in bW make less difference. Because of their higher reproductive rate, inland subpopulations are initially less affected by winter habitat loss than coastal subpopulations. These conclusions are robust over a range of assumptions about competition for territories in summer and age difference in mortality in winter. 4. Adding density-dependent fledging success to the basic model reduces the effect of winter habitat loss on population size, but only when low proportions of the habitat are removed. A higher mortality rate in females, whether only in post-fledging young birds or in birds of all ages, makes little additional difference to the population consequences of habitat loss. 5. Field studies on winter habitat loss in migratory bird populations should first test whether density has already reached the critical level, cW; i.e. whether some birds already die of food competition. The parameter bW should then be estimated to determine whether its probable value lies in the range within which predictions are sensitive or insensitive to its precise value. Whether the summer density-dependent functions are linear or curvilinear needs also to be explored, as does the effect of interactions between subpopulations which have different fledgling production rates but share the same winter habitat.
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Biological invasions are a major global environmental and economic problem. Analysis of the San Francisco Bay and Delta ecosystem revealed a large number of exotic species that dominate many habitats in terms of number of species, number of individuals and biomass, and a high and accelerating rate of invasion. These factors suggest that this may be the most invaded estuary in the world. Possible causes include a large number and variety of transport vectors, a depauperate native biota, and extensive natural and anthropogenic disturbance.
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Spartina alterniflora was first introduced into south San Francisco Bay in the 1970’s. Since that time it has spread to new areas within the south bay and is especially well established at four sites. The spread of this introduced species was evaluated by comparing its vegetative and reproductive characteristics to the native cordgrass, Spartina foliosa. The characters studied were intertidal distribution, phenology, aboveground and belowground biomass, growth rates, seed production, and germination rates. Spartina alterniflora has a wider intertidal distribution than S. foliosa and outproduced the native cordgrass in all aspects that were studied. These results indicate that the introduced species has a much better chance of becoming established in new areas than the native species, and once established, it spreads more rapidly vegetatively than the native species. Spartina alterniflora is likely to continue to spread to new areas in the bay and displace the native plant. In addition, this introduced species may effect sedimentation dynamics, available detritus, benthic algal production, wrack deposition and disturbance, habitat structure for native wetland animals, benthic invertebrate populations, and shorebird and wading bird foraging areas. *** DIRECT SUPPORT *** A01BY058 00013
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Along the Pacific coast of North America, four introduced cordgrass species (Spartina alterniflora, S. anglica, S. patens and S. densiflora) have thus far invaded five isolated estuaries. Dense growth of introduced Spartina spp. reduces open mud feeding habitats of shorebirds, while in the upper intertidal, introduced Spartina spp. compete with native salt marsh vegetation. Prediction of Spartina invasions is facilitated by the remarkable restriction of these species to distinct estuarine habitats which generally lack interspecific competitors and herbivores. We used physical characteristics to identify 31 specific sites along the US Pacific coast that are vulnerable to future Spartina invasions and then used species characteristics, like native latitudinal range and past invasion success, to predict which Spartina species will be likely to invade these sites in the future. All 31 sites were predicted to be vulnerable to S. alterniflora, while the other invasive Spartina 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 used to predict the extent of spatial spread of a Spartina sp. after colonization. These prediction techniques might be used to identify and prioritize sites for protection against future invasions. We suggest that a cost-effective way to prevent the transformation of unique North American Pacific mudflat and saltmarsh communities into introduced Spartina-dominated marshes is to survey the vulnerable sites frequently and eliminate introduced Spartina spp. propagules before they spread.
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Thesis (Ph. D.)--Dept. of Biological Sciences, Stanford University. Bibliography: l. 91-92.
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Diversity in the tRNALEU1 intron of the chloroplast genome of Spartina was used to study hybridization of native California cordgrass, Spartina foliosa, with S. alterniflora, introduced to San Francisco Bay approximately 25 years ago. We sequenced 544 bases of the tRNALEU1 intron and found three polymorphic sites, a pyrimidine transition at site 126 and transversions at sites 382 and 430. Spartina from outside of San Francisco Bay, where hybridization between these species is impossible, gave cpDNA genotypes of the parental species. S. foliosa had a single chloroplast haplotype, CCT, and this was unique to California cordgrass. S. alterniflora from the native range along the Atlantic coast of North America had three chloroplast haplotypes, CAT, TAA, and TAT. Hybrids were discriminated by random amplified polymorphic DNA (RAPD) phenotypes developed in a previous study. We found one hybrid that contained a cpDNA haplotype unknown in either parental species (TCT). The most significant finding was that hybridization proceeds in both directions, assuming maternal inheritance of cpDNA; 26 of the 36 hybrid Spartina plants from San Francisco Bay contained the S. foliosa haplotype, nine contained haplotypes of the invading S. alterniflora, and one had the cpDNA of unknown origin. Furthermore, cpDNA of both parental species was distributed throughout the broad range of RAPD phenotypes, suggesting ongoing contributions to the hybrid swarm from both. The preponderance of S. foliosa cpDNA has entered the hybrid swarm indirectly, we propose, from F1s that backcross to S. foliosa. Flowering of the native precedes by several weeks that of the invading species, with little overlap between the two. Thus, F1 hybrids would be rare and sired by the last S. foliosa pollen upon the first S. alterniflora stigmas. The native species produces little pollen and this has low viability. An intermediate flowering time of hybrids as well as pollen that is more vigourous and abundant than that of the native species would predispose F1s to high fitness in a vast sea of native ovules. Thus, spread of hybrids to other S. foliosa marshes could be an even greater threat to the native species than introductions of alien S. alterniflora.
Spartina salt marshes in southern England
  • D S Ranwell
Ranwell, D. S. 1964. Spartina salt marshes in southern England. Journal of Ecology 49: 325-374.