Information about common cordgrass (Spartina anglica)

Common Cordgrass (Spartina anglica C.E. Hubbard)

Family: Gramineae (Poaceae)Family: Gramineae (Poaceae)

Description and Variation: Spartina anglica is a stout, rhizomatous salt marsh grass that spreads by clonal growth, often forming extensive meadows (Thompson 1991). The stiff plant may be 5 to 100 cm tall, with stout stems five mm or more in diameter. The leaves lack auricles and have ligules that consist of a fringe of hairs. The leaf blades, which may be flat or inrolled, are 5 to 12 mm broad and may be persistent or falling. The flowers occur in numerous, erect, contracted panicles, which consist of closely overlapping spikelets in two rows on one side of the rachis (Partridge 1987). S. anglica is closely related Spartina x townsendii; both result from a hybrid of Spartina maritima and Spartina alterniflora. However, S. anglica is the F2 generation and produces fertile seed, while S. x townsendii does not.

Perhaps as a result of its hybrid origins, there is considerable morphological variation in S. anglica. Variable characteristics include shoot density, vegetative vigor, density of inflorescences, flowering times, seed production, and seed germination (Hubbard 1965).

Spartina Spartina is a relatively small genus consisting of approximately 14 species, geographically centered along the east coast of North and South America, with outliers on the west coast of North America, Europe, and Tristan da Cunha. Members of the genus occur primarily in wetlands, especially estuaries (Partridge 1987). However, no Spartina species are native to the intertidal zone in Washington (Ebasco Environmental 1992a).

Economic Importance: Beneficial - Spartina anglica has been planted around the world for a variety of reasons. Because of its ability to trap sediment, navigational interests have used S. anglica to stabilize mudflats and reduce the source area for channel silting (Ranwell 1967). The species has also been planted to protect coastlines from erosion (Ranwell 1967; Gray et al. 1991). In addition, agricultural interests have planted S. anglica for estuary reclamation (Ranwell 1967; Partridge 1987; Gray et al. 1991). In England, S. townsendii is widely used by livestock, and experience from around the world indicates a wide variety of herbaceous mammals will eat S. anglica or S. townsendii (Ranwell 1967). S. anglica is also used as green manure in China; 50 kg of S. anglica are approximately equivalent to 0.5 kg of urea (Chung 1982).

Detrimental - Some of the very traits that make Spartina anglica valued are also the greatest causes for concern. In Washington, the greatest concern is the species’ ability to trap large amounts of sediment. S. anglica’s stout stems and leaves slow tidal water, thus trapping sediment (mostly in the leaf axes). As portions of the plant age and fall off, the sediment is deposited at the base of the plant and then bound by the extensive rhizomes (Thompson 1991). S. anglica sediment accretion rates are higher than those of other salt marsh vegetation and other Spartina species (Lee and Partridge 1983). As a result, S. anglica causes tidelands to rise more than they would if they were unvegetated or vegetated by other species (Thompson 1991). No information is currently available on the sediment accretion rate of S. anglica marshes in Washington, but published data from other parts of the world create cause for concern. In Europe, sedimentation rates of 20 to 200 mm/yr. are reported (Ranwell 1967; Lee and Partridge 1983; Thompson 1991), and as much as six feet of accreted sediment occurs under some British S. anglica marshes (Ranwell 1967; Gray et al. 1991). Sedimentation rates of up to 260 mm/year have been reported in China, where S. anglica was intentionally introduced (Chung 1990 cited in Gray et al. 1991). In contrast, a study of low intertidal salt marshes in Washington and Oregon that lacked Spartina found that the sediment accretion rate ranged from 2.3 to 6.6 mm/yr., with a mean of 3.6 mm/yr. (Thom 1992). Before Spartina colonization, Pacific Northwest estuaries consisted primarily of bare, gently-sloping mudflats with shallow tidal channels. S. anglica replaces gradually sloping mudflats with badly drained marshes (Gray et al. 1991) that commonly have steeply sloping seaward edges and deep, steep-sided channels. In addition, infestations of S. anglica may block some navigational channels (Ranwell 1967). - Some of the very traits that make Spartina anglica valued are also the greatest causes for concern. In Washington, the greatest concern is the species’ ability to trap large amounts of sediment. S. anglica’s stout stems and leaves slow tidal water, thus trapping sediment (mostly in the leaf axes). As portions of the plant age and fall off, the sediment is deposited at the base of the plant and then bound by the extensive rhizomes (Thompson 1991). S. anglica sediment accretion rates are higher than those of other salt marsh vegetation and other Spartina species (Lee and Partridge 1983). As a result, S. anglica causes tidelands to rise more than they would if they were unvegetated or vegetated by other species (Thompson 1991). No information is currently available on the sediment accretion rate of S. anglica marshes in Washington, but published data from other parts of the world create cause for concern. In Europe, sedimentation rates of 20 to 200 mm/yr. are reported (Ranwell 1967; Lee and Partridge 1983; Thompson 1991), and as much as six feet of accreted sediment occurs under some British S. anglica marshes (Ranwell 1967; Gray et al. 1991). Sedimentation rates of up to 260 mm/year have been reported in China, where S. anglica was intentionally introduced (Chung 1990 cited in Gray et al. 1991). In contrast, a study of low intertidal salt marshes in Washington and Oregon that lacked Spartina found that the sediment accretion rate ranged from 2.3 to 6.6 mm/yr., with a mean of 3.6 mm/yr. (Thom 1992). Before Spartina colonization, Pacific Northwest estuaries consisted primarily of bare, gently-sloping mudflats with shallow tidal channels. S. anglica replaces gradually sloping mudflats with badly drained marshes (Gray et al. 1991) that commonly have steeply sloping seaward edges and deep, steep-sided channels. In addition, infestations of S. anglica may block some navigational channels (Ranwell 1967).

A secondary impact of increased sediment accretion may be changes in water circulation patterns. Sediment accretion associated with S. anglica infestations in England has been known to reduce tidal flow (Hubbard 1965). In New Zealand, where S. anglica was intentionally introduced, it has trapped so much sediment that the previously existing salt marshes behind the Spartina have become slight depressions. By this process, S. anglica impedes drainage, resulting in flooding from trapped, backed up water (Partridge 1987). Large, dense populations at or in river mouths may cause particular problems by decreasing flow and leading to increased flooding, especially during periods of heavy precipitation and/or above normal tides (Ebasco Environmental 1993).

Detrimental effects of S. anglica infestations extend beyond increases in sedimentation. Doody (1990 cited in Gray et al 1991) summarized the negative impacts of S. anglica in Britain as follows:

Invades mudflats rich in invertebrates and used by overwintering shorebirds and waterfowl;
Replaces more diverse plant communities;
Produces dense, monotypic stands that alter succession and are replaced in ungrazed areas by equally species-poor communities; and
Promotes agricultural reclamation that results in the destruction of species-rich salt marsh habitats.

For the most part, detailed studies have not been conducted on the specific impacts of S. anglica in Washington. However, studies are available from other parts of the world. In Britain, the spread of S. anglica has been associated with the decline of some bird populations by as much as 50 percent in affected areas. Birds most affected were those that prefer to feed on open mud. Studies of the dunlin (Calidris alpina) found that populations declined most in estuaries where S. anglica had spread the most, while population numbers remained unchanged where S. anglica populations were static. Control and removal of S. anglica infestations resulted in the return of the dunlin (Gray et al. 1991). The exact cause of these patterns has not been investigated thoroughly, but S. anglica may remove feeding areas and reduce feeding time, resulting in increased emigration and mortality (Gray et al. 1991).

Some of the impacts of S. alterniflora, another noxious Spartina of the intertidal zone in Washington, may also apply to S. anglica. S. alterniflora may displace native plants, such as Zostera marina (seagrass) at lower elevations, and salt marsh species, such as Salicornia virginica, Triglochin maritimum, Jaumea carnosa, and Fucus distichus at higher elevations (Wiggins and Binney 1987; Simenstad and Thom 1995). At this time, most evidence of species displacement is anecdotal, but displacement of several of these plants is of particular concern. Seagrasses (Zostera spp.), for example, provide important refuge and food sources for fish, crabs, waterfowl, and other marine life (Balthuis and Scott 1993). As unvegetated mudflats are replaced by salt marshes, bottom-dwelling invertebrate communities will be replaced by salt marsh species. Studies indicate that populations of invertebrates in the sediments of S. alterniflora clones in Willapa Bay are smaller than populations in intertidal mudflats (Norman and Patten 1994b). Even in its native area, the benthic fauna of S. anglica marshes is generally depleted in comparison to nearby tideflats (Gray et al. 1991). As Spartina infestations expand, shorebirds and waterfowl will lose potentially important foraging and refuge habitat. In the Willapa National Wildlife Refuge, S. alterniflora has displaced an estimated 16 to 20 percent of critical habitat for wintering and breeding aquatic birds (Foss 1992). Juvenile chum salmon and English sole may lose prey resources and other important attributes of mudflat nurseries. In short, mud- and sandflat communities based on bottom-dwelling microalgae will decline, being replaced by food webs driven by the supply of Spartina detritus (Simenstad and Thom 1995).

Changes associated with Spartina also impact recreation. Loss of beach habitat and navigation routes, reduced water access, and other alterations to the estuarine ecosystem may result from the spread of S. anglica. Therefore, activities, such as fishing, hunting, boating, bird watching, botanizing, and shellfish harvesting, that are dependent on the extant intertidal ecosystem could be negatively impacted by the continued spread of Spartina (Ebasco Environmental 1993).

Geographic Distribution: A hybrid between the British Spartina maritima and the North American S. alterniflora, S. anglica originated on the British coast in the nineteenth century, and it is now widespread throughout British coastal areas. The natural distribution of S. anglica is thought to be between Poole, Dorset, and Pagham, Sussex and possibly northern France. All other populations around the world are intentional introductions (Raybould et al. 1991b). On the European coast, populations occur between 48° and 57.5° N (Ranwell 1967). Worldwide, S. anglica is known from Ireland, Denmark, Germany, Netherlands, Australia, New Zealand, China, and the United States (Ranwell 1967; Chung 1982). Some introduced populations are quite large. In China, descendants of only 21 individuals spread to cover more than 36,000 hectares by 1980 (Gray et al. 1991). However, attempts to establish S. anglica in subtropical and tropical areas have failed (Ranwell 1967).

In Washington, S. anglica occurs in Skagit, Island, Snohomish, San Juan, Kitsap, Jefferson, and King counties (Adopt a Beach, unpublished data), with the largest populations in Island, Snohomish and Skagit counties. S. anglica has not been recorded from British Columbia or Oregon, but it does occur in San Francisco Bay (Spicher and Josselyn 1985; Ebasco Environmental 1992a).

Habitat: Spartina anglica is a plant of the intertidal zone. Because of its phenotypic plasticity, the species can tolerate a wide range of environmental conditions (Gray et al. 1991; Thompson 1991). The plant occurs on a variety of substrates, including clays, fine silts, organic muds, sands, and shingle (Gray et al. 1991). S. anglica can tolerate inundation for nine hours or more, which is greater than the tolerance of other species (Ranwell 1967; Thompson 1991). As result, S. anglica can occupy the seaward edge of salt marshes where there is little or no competing vegetation (Ranwell 1967; Gray et al. 1991). In Britain, S. anglica occurs as a belt of vegetation just seaward of other vegetation. Individual clumps may be found at higher elevations, with the species’ upper limit probably determined by competition from other vegetation (Gray et al. 1991). At lower elevations, the distribution of S. anglica may be limited by wave action; the species is more successful in sheltered sites, possibly because wave action uproots seedlings (Chung 1982; Gray et al. 1991).: Spartina anglica is a plant of the intertidal zone. Because of its phenotypic plasticity, the species can tolerate a wide range of environmental conditions (Gray et al. 1991; Thompson 1991). The plant occurs on a variety of substrates, including clays, fine silts, organic muds, sands, and shingle (Gray et al. 1991). S. anglica can tolerate inundation for nine hours or more, which is greater than the tolerance of other species (Ranwell 1967; Thompson 1991). As result, S. anglica can occupy the seaward edge of salt marshes where there is little or no competing vegetation (Ranwell 1967; Gray et al. 1991). In Britain, S. anglica occurs as a belt of vegetation just seaward of other vegetation. Individual clumps may be found at higher elevations, with the species’ upper limit probably determined by competition from other vegetation (Gray et al. 1991). At lower elevations, the distribution of S. anglica may be limited by wave action; the species is more successful in sheltered sites, possibly because wave action uproots seedlings (Chung 1982; Gray et al. 1991).

History: Spartina anglica is the product of a cross between two other Spartina species: S. maritima and S. alterniflora. S. maritima is a native of Britain, whereas S. alterniflora is a North American native that was probably introduced to Britain via ship traffic (Hubbard 1965). The original cross is thought to have occurred in Hampshire, Britain around 1870 (Raybould et al. 1991b), and it resulted in a sterile hybrid, S. x townsendii. The hybridization brought together maternal and paternal chromosomes that were too dissimilar to pair up during meiosis, so sterile gametes were produced. However, when the chromosomes replicated to produce two copies of each parental chromosome, the chromosomes were then able to form bivalent pairs in meiosis, which resulted in a fertile polyploid (having more than two complete sets of chromosomes per nucleus) (Thompson 1991). This fertile hybrid is S. anglica. Although S. x townsedii and S. anglica differ in their chromosome number and fertility, they are very difficult to differentiate morphologically (Hubbard 1978).

S. anglica S. anglica spread rapidly in Britain. By 1907, it was brought to the attention of the Royal Commission on Coast Erosion, which resulted in a research program on Spartina for coastal protection and reclamation. A report to the Dutch government in 1923 led to the export of Spartina plant fragments from Poole Harbor, Britain to the Netherlands. The Dutch felt their research trials were successful and, in 1929, published a pamphlet, "Economic Possibilities of Rice Grass," which was quoted in newspapers around the world. This publicity led to numerous requests for Spartina plant fragments and seed. Between 1924 and 1936, more than 175,000 fragments and many seed samples from Poole Harbor were sent to more than 130 sites around the world (Hubbard 1965). Because S. anglica in Britain has very low genetic variability, it appears that two closely related genotypes or an extremely restricted range of genotypes have colonized a wide area via natural spread and deliberate introductions (Raybould et al. 1991b).

In Washington, the U.S. Department of Agriculture and Washington State University introduced S. x townsedii/S. anglica to the Stillaguamish estuary in Port Susan Bay in 1961 or 1962 (Spicher and Josselyn 1985). The original introduction was made to provide forage for cattle, and it was supposed to be the sterile S. x townsendii (Spicher and Josselyn 1985; Ebasco Environmental 1992a). However, the plants are now known to be the fertile S. anglica (Spicher and Josselyn 1985; Frenkel and Kunze 1984 cited in Aberle 1990). It is not clear whether the original planting was actually S. anglica or if it was S. x townsendii and a natural chromosome doubling then produced S. anglica (Ebasco Environmental 1992a). S. anglica has spread rapidly since its introduction to Puget Sound. Populations have spread as far south as Vashon Island and as far north as San Juan Island. S. anglica from Puget Sound was also intentionally introduced to San Francisco Bay in 1977 (Spicher and Josselyn 1985).

Physiology: Unlike many temperate grasses, S. anglica has a C₄ photosynthetic pathway. (C₄ refers to the number of carbons produced in the first step of photosynthesis). At optimal temperatures, C₄ species have greater nitrogen and water-use efficiency than comparable C₃ species, which may help explain the high salinity tolerance of S. anglica. In addition, like other C₄ species, S. anglica can photosynthesize at a much greater rate than C₃ plants when the temperature is above 10° C. However, unlike other C₄ species in northwest Europe, S. anglica can maintain photosynthetic rates at 5° to 10° C. that are equivalent to C₃ rates. Therefore, it does not have the temperature constraints that limit other C₄ plants to lower latitudes (Gray et al. 1991; Thompson 1991).

Growth and Development: Spring through early fall is a time of rapid growth and flowering for Spartina anglica. In late fall, the flowering culms generally die; however, flowering may extend to the following year during mild winters. In November, S. anglica produces overwintering buds in the leaf axils, which is followed by rhizome development in response to short days (Gray et al. 1991). Rhizome biomass peaks in early winter to make up 50 percent of S. anglica’s belowground biomass (Gray et al. 1991).: Spring through early fall is a time of rapid growth and flowering for Spartina anglica. In late fall, the flowering culms generally die; however, flowering may extend to the following year during mild winters. In November, S. anglica produces overwintering buds in the leaf axils, which is followed by rhizome development in response to short days (Gray et al. 1991). Rhizome biomass peaks in early winter to make up 50 percent of S. anglica’s belowground biomass (Gray et al. 1991).

S. anglica S. anglica spread generally occurs in three phases. An initial colonization period occurs for one to two years, followed by slow clonal growth as seedlings establish. Once established, plants experience a burst of prolific clonal expansion. Throughout the different phases, seed production varies. Pioneer populations often produce little seed, but seed production increases with marsh development (Thompson 1991).

Die-back of unknown cause(s) is apparent in many mature Spartina meadows in Britain. (Hubbard 1965; Gray et al. 1991; Thompson 1991). This phenomenon occurs most frequently in badly drained, waterlogged marshes that have highly anaerobic soils, a high proportion of fine particles, and a high sulphide content. Toxic levels of sulfide and anoxia in rhizomes have been implicated in the death of these plants (Gray et al. 1991).

Reproduction: A rhizomatous perennial, Spartina anglica spreads via seed, rhizomes, tillering, and rhizome fragments (Ebasco Environmental 1992a). In Washington, the species can flower as early as April (personal observation), and flowering continues through the summer. Seed production in the species is quite variable - both temporally and spatially. In England, flowers emerging in July and August ripen seed within approximately 12 weeks, while those flowering in September may not have time to mature (Mullins and Marks 1987). S. anglica appears to have a self-incompatibility system, although some unknown conditions cause this system to break down, resulting in seed set. Higher than average temperatures and humidity may result in a breakdown in incompatibility, but detailed studies have not been done (Gray et al. 1991).

S. anglica S. anglica seeds are relatively short-lived. In England, seeds are only viable for one season under field conditions, with germination rates of 0.6 to 5 percent (Ebasco Environmental 1992). Laboratory studies have indicated that seeds stored at 4° C. in a refrigerator remained viable for at least four years. Maximum germination occurred in the dark, with the germination rate increasing as temperatures increased from 7° to 25° C (Hubbard 1970).

Seeds buried between 1 and 3 cm have the best chance of establishing. At shallower depths, seeds are subject to desiccation, while deeper burial may result in decreased viability (Groenendijk 1986 cited in Gray 1991). On bare mud, S. anglica seedlings may grow densely, occurring at densities up to 13,000/m². Densities are lower in meadows (up to 9750/m²), with many of the seedlings dying. In most cases, meadows are maintained by rhizome formation and tillering, rather than seedling establishment (Gray et al. 1991).

Response to Mechanical Methods: Seedlings can be pulled out effectively. Care must be taken to remove both shoots and roots. Seedlings generally begin tillering late in their first growing season. Once the plant has tillered, hand-pulling may break off portions of root, allowing the plant to resprout. Repeated pulling will eventually kill small plants (Spartina Task Force 1994). However, pulling or digging established clones is difficult and largely ineffectual. Attempts to remove a 1 m x 2 m S. alterniflora clone in Willapa Bay indicate it is difficult to remove all roots and rhizomes, and the amount of wet mud that is removed in the digging process makes the technique unmanageable (Aberle 1990).

Covering small Spartina clones with woven geotextile fabric has been successful in some areas. With this technique, clones are mown to ground level and covered out 3 to 4 feet beyond the edges of the clone. The covering must be anchored in place. To be effective, covering should be left in place for one to two growing seasons. This method is most suitable for small infestations. (Spartina Task Force 1994).

Mowing infestations can contain growth, limit seed set, and eventually kill the plants. To be effective, clones must be mowed repeatedly, beginning with initial spring green-up and continued until fall die-back. For clones under 10 feet in diameter, one to three mowings during the growing season may be effective. Larger clones need to be mowed nine to ten times over two seasons for eradication. In some cases, mowing will be required for a third or fourth year (Spartina Task Force 1994).

Response to Cultural Methods: Diking can be used as a containment measure, since dikes confine the lateral spread of rhizomes. Dikes also remove tidal action, thereby inhibiting nutrient flow and oxygen exchange. In addition, dikes can be used to flood areas, which will eventually bring about Spartina death. However, flooding will also kill other species that cannot tolerate prolonged submersion. From a practical standpoint, diking is not appropriate for large areas; it would work best in small lagoons that only need to be diked on one side (Aberle 1990).

Response to Herbicides:

In general, data from herbicide trials (Norman and Patten 1995b) in Willapa Bay suggest:

Treatment efficacy is influenced by time of application: June > July > August > May.
Treatment efficacy is influenced by application method: hand-held wipe > hand-held backpack>simulated aerial.
Treatment costs: hand-held backpack > hand-held wipe > simulated aerial.

Biocontrol potential: Because Spartina anglica is a new species, there is a relative absence of herbivores or diseases that affect the plant, even in its native habitat (Gray et al. 1991). However, because of its low levels of genetic variability and the fact that it spreads largely by vegetative means, S. anglica is potentially vulnerable to parasite and pathogen infestation (Thompson 1991).

Recently, there has been a rise in infection with the ergot fungus (Claviceps purpurea (Fr.) Tul.) on S. anglica populations in Britain. Ergot infects flower parts and replaces grain with sclerotia (a hardened mass of filaments), which could potentially reduce seed production (Ebasco Environmental 1992c). In England, ergot has reached epidemic proportions, with more than 90 percent of the flowering heads infected in some populations (Gray et al. 1991). Ergot infects many other grasses besides Spartina, including rye, wheat, barley, and oats. However, since C. purpurea is host-specific, the strain that occurs on S. anglica is probably a distinct taxon. Therefore, ergot might have potential as a biocontrol agent, but additional research is needed.

Rationale for listing: Spartina anglica is an aggressive exotic salt marsh plant that has already colonized a significant areas of Puget Sound. Without question, Spartina invasions in Washington bring about change to the intertidal zone (Simenstad and Thom 1995). While the exact ecological and economic consequences of these changes is uncertain, the potential for damage is extensive. The only way to test the full extent of the impacts would to wait until S. anglica is widely established, at which point, the species would be virtually impossible to control (Spicher and Josselyn 1992). The Washington State Noxious Weed Control Board views this possibility as an unacceptable risk. Therefore, prevention of seed production in all designated areas is required to help contain this species and prevent its further spread.

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