Economic  Importance:  Beneficial: In its native habitat, Spartina alterniflora is valued (Simenstad and Thom 1995; Landin 1991). The species is highly productive, exporting approximately 1300 g/m² of detritus annually to the estuarine system (Landin 1991). S. alterniflora is also highly regarded for erosion control, as well as fish and wildlife values in its native range (Simenstad and Thom 1995). In these native habitats, some waterfowl and wetland mammals eat the roots and shoots of this plant. In addition, stands of S. alterniflora can serve as a nursery area for mangroves, and estuarine fishes and shellfishes.

Because of their ability to trap sediment, Spartina species have been planted in many parts of the world for estuary reclamation (Partridge 1987). While S. anglica has been used more commonly for this purpose, S. alterniflora has been planted in some areas, such as the North Island of New Zealand (Partridge 1987).

In Pacific Northwest estuaries, species that are able to utilize S. alterniflora marshes could benefit from the expansion of this species. For example, juvenile chinook salmon have an affinity for salt marsh habitat, so they may benefit from the spread of salt marsh vegetation (Simenstad and Thom 1995).

There are also some economically beneficial uses for Spartina alterniflora. The species is palatable to livestock, so the plant’s continued spread may increase available pasture. Efforts have also been made to use S. alterniflora in paper production (Ebasco Environmental 1993).

Detrimental: Some of the very traits that make Spartina alterniflora valued in its native habitat are the greatest cause for concern in Washington. To understand the different east/west perspectives on the values of Spartina, it is important to recognize that Atlantic/Gulf coast estuaries are fundamentally different than their Pacific Coast counterparts. The Pacific Coast is macrotidal, while the Atlantic/Gulf coasts are microtidal (Simenstad and Thom 1995). In addition, the Pacific Coast is more geologically active, and tectonic activity has a much greater influence on coastal marsh systems. Subsidence due to compaction of marsh soils that results from insufficient sediment supply is less important on the Pacific Coast (Thom 1992). Finally, on the East Coast, the prevailing wisdom is that salt marshes are the key to productivity of estuarine systems because of the contribution of their detritus. However, on the West Coast, secondary productivity from tidal mudflats is more important than detritus exported from salt marshes (Hedgepeth 1978 c.f. Pierce 1982). Some of the very traits that make Spartina alterniflora valued in its native habitat are the greatest cause for concern in Washington. To understand the different east/west perspectives on the values of Spartina, it is important to recognize that Atlantic/Gulf coast estuaries are fundamentally different than their Pacific Coast counterparts. The Pacific Coast is macrotidal, while the Atlantic/Gulf coasts are microtidal (Simenstad and Thom 1995). In addition, the Pacific Coast is more geologically active, and tectonic activity has a much greater influence on coastal marsh systems. Subsidence due to compaction of marsh soils that results from insufficient sediment supply is less important on the Pacific Coast (Thom 1992). Finally, on the East Coast, the prevailing wisdom is that salt marshes are the key to productivity of estuarine systems because of the contribution of their detritus. However, on the West Coast, secondary productivity from tidal mudflats is more important than detritus exported from salt marshes (Hedgepeth 1978 c.f. Pierce 1982).

In Washington, one of the greatest causes for concern over S. alterniflora is the species’ ability to trap sediment. On the East and Gulf coasts, where S. alterniflora is a major component of salt marsh vegetation, sediment accretion rates can be as high as 13 mm/year, with higher stem densities resulting in higher sediment deposition rates and steeper beach profiles (Simenstad and Thom 1995; Gleason et al. 1979). Where S. alterniflora has been introduced to San Francisco Bay, sediment accretion rates have been estimated at 1.4 to 13.3 mm/yr. (Callaway 1990; Josselyn et al. 1993 c.f. Simenstad and Thom 1995). In contrast, a study of low intertidal salt marshes in Washington and Oregon that lacked S. alterniflora 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). This higher rate of accretion rate associated with Spartina may change the fundamental nature of portions of Washington’s coastline. Before S. alterniflora colonization, pacific northwest estuaries consisted primarily of bare, gently-sloping mud flats with shallow tidal channels. Fully developed Spartina marshes have steeply sloping seaward edges and deep, steep-sided tidal channels. S. alterniflora clones trap sediment, causing the clones to rise above the surrounding tideflat (Ebasco Environmental 1992a). Higher stem densities dissipate more wave action, resulting in greater sediment deposition and steeper beach profiles (Gleason et al. 1979).

A secondary impact of increased sediment accretion may be changes in water circulation patterns. Sediment accretion associated with Spartina anglica infestations in England has been known to reduce tidal flow (Hubbard 1965). In addition, large, dense populations at or in river mouths may decrease flow and lead to increased flooding, especially during periods of heavy precipitation and/or above normal tides (Ebasco Environmental 1993).

The spread of Spartina can also impact the native flora and fauna of the intertidal zone. Spartina 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 saltmarsh 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). Loss of habitat for bivalves is of particular concern to the $16 million oyster industry in Willapa Bay. 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 S. alterniflora detritus (Simenstad and Thom 1995). A summary of potential impacts is summarized in Table 1. 

Table 1. Potential impacts of Spartina alterniflora spread in Washington State (adapted from Callaway and Josselyn 1992).

Changes associated with Spartina also have the potential to 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. alterniflora. 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).

Geographical Distribution: Spartina alterniflora is native to the Atlantic and Gulf coasts of North America, occurring from Quebec and Newfoundland to Florida and Texas (Hitchcock 1971). A similar species, S. brasiliensis Raddi, occurs along the eastern seaboard of South America, and some taxonomists lump S. brasiliensis under S. alterniflora (Marchant 1970). In its native range, S. alterniflora is the dominant salt marsh plant, forming dense single species stands along the seaward edge of marshes (Metcalfe et al. 1986). It has been both intentionally and accidentally introduced to numerous other regions of the world, including Great Britain and the Atlantic coast of Europe, New Zealand, and the Pacific coast the U.S. (Marchant 1970; Hitchcock 1971; Partridge 1987). 

In California, S. alterniflora is known from San Francisco Bay and Humboldt Bay (Daehler and Strong 1994; Spicher and Josselyn 1985). The only known Oregon population occurs in the Siuslaw estuary, where it was experimentally established in the late 1970’s from stock obtained in Georgia (Frenkel 1987; Frenkel 1990).

Washington’s largest population is in Willapa Bay (Pacific County), where S. alterniflora clones/meadows cover an estimated 1850 acres, and seedlings occupy another 6500 acres (Washington Department of Natural Resources 1992, unpublished data). Populations are also found in Grays Harbor County in the Copalis River estuary and at Damon Point in Grays Harbor. In addition, the plant has invaded areas of Puget Sound and the Strait of Juan de Fuca, including: Sequim Bay (Clallam County), Thorndyke Bay and Kala Point (Jefferson County), and Padilla Bay (Skagit County) (Adopt a Beach, unpublished data; Ebasco Environmental 1992). As of 1991, 19 S. alterniflora stands covered an estimated 48,100 m² in Padilla Bay (Riggs 1992).

Habitat: Spartina alterniflora is a plant of the intertidal zone, where it colonizes mud- or sandflats in saline or brackish water. Found in areas of low to moderate wave energy, the species can colonize a broad range of substrates, ranging from sand and silt to loose cobble, clay, and gravel. The species can tolerate a wide range of environmental conditions, including: inundation up to 12 hours a day, pH levels from 4.5 to 8.5, and salinity from 10 to 60 ppt, although 10-20 ppt is optimal (Landin 1990).

In its native range, S. alterniflora typically exclusively dominates low salt marshes (Bertness 1991), growing from 0.7 m below mean sea level to approximately mean high water (Landin 1990). In Willapa Bay, the plants have been observed growing between 1.75 and 2.75 m above mean lower low water (MLLW), and transplants have been known to survive within 1 m above MLLW (Sayce 1988). S. alterniflora occurs both on the periphery of Willapa Bay and up some of the rivers, within areas of saline tidal influence (Kunz and Martz 1993).

In areas of Washington, such as Padilla Bay, S. alterniflora appears to grow at lower tidal elevations than native salt marsh species; no other plants are found on the seaward side of S. alterniflora (Balthuis and Scott 1993; Wiggins and Binney 1987). Spartina usually occurs in a single species stand, although there can be community overlap at the edge of some salt marshes (Wiggins and Binney 1987; Kunz and Martz 1993). In these areas, Spartina may occur with Salicornia virginica (pickleweed), Triglochin maritimum (seaside arrowgrass), Jaumea carnosa (fleshy jaumea), Distichlis spicata (saltgrass), and Deschampsia caespitosa (tufted hairgrass) (Kunz and Martz 1993; Sayce 1988; Simenstad and Thom 1995; Riggs 1992; Wiggins and Binney 1987; Balthuis and Scott 1993).

History:  Spartina alterniflora was apparently first introduced into Willapa Bay in 1894 in a shipment of eastern oyster spat originating from the east coast of North America. Initially, the species established on the west side of Long Island (Sayce 1988). However, the plant was not accurately identified until 1940’s, when the plants flowered (Scheffer 1945; Sayce 1988). The clumps, which covered several acres at that time, had first been noted around 1911 (Scheffer 1945). During the first 50 years, the population expanded slowly, but from 1945 to 1988 the plant became established throughout the bay (Sayce 1988).

In Puget Sound, S. alterniflora was introduced to stabilize shorelines and increase vegetative cover. The Dike Island Gun Club planted S. alterniflora in Padilla Bay in the 1940’s to stabilize an island in the south bay. By 1991, the plant covered an estimated 12 acres. S. alterniflora was also introduced to Thorndyke Bay, Kala Point, and Sequim Bay to increase vegetative cover (Ebasco Environmental 1992).

Growth and Development: Spartina alterniflora is a rhizomatous perennial, which, under favorable conditions, can reach sexual maturity in three to four months (Smart 1982). Mature plants produce seed in the fall. Seeds require soaking for approximately six weeks to germinate, with most seeds germinating in the spring. The seeds are short-lived (roughly 8 months), so the species does not have a persistent seed bank (Sayce and Mumford 1990). Germination rates are variable. Callaway and Josselyn (1992) found that roughly 37.3% of seeds collected in San Francisco Bay germinated, while Sayce (1988) found only a 0.04% germination rate for seeds collected in Willapa Bay. However, different pre-treatments were used in the two studies, and the pre-treatment of the Willapa Bay seeds may have been insufficient to break dormancy. In Willapa Bay, millions of germinating seeds are visible in the high intertidal drift zone during the winter. These seeds are probably broadcast throughout the bay with spring tides (Simenstad and Thom 1995).

While seeds are important for colonizing new areas, they appear to be unimportant in maintaining established stands. Studies in Rhode Island suggest that S. alterniflora seedlings are unable to survive under adult canopy, and seedling success increases with the size of bare patches (Metcalfe et al. 1986). Therefore, the expansion of established stands is due to vegetative growth. In some areas, S. alterniflora has demonstrated the ability to rapidly colonize bare areas due to a high intrinsic growth rate and rapid propagation of stems via rhizomes (Smart 1982). Estimates of lateral growth taken in Washington indicate that clones expand at approximately 0.5 to 1.7 m/yr. (Riggs 1992; Simenstad and Thom 1995; Sayce 1988).

On the West Coast, S. alterniflora is able to extend to lower intertidal elevations than native species, so it frequently grows without competition from macrovegetation (Callaway and Josselyn 1992; Riggs 1992). In the low oxygen environment of this habitat, many plant species are unable to utilize nutrients in the substrate. However, S. alterniflora is able to mobilize nutrients under low oxygen conditions through rhizosphere oxidation. (The rhizosphere is the soil zone of increased microbial activity surrounding the roots). S. alterniflora has a large amount of internal gas spaces (aerenchyma) that extend from the leaves to the root tips. These spaces function as conduits for gas exchange between the plant and the rhizosphere. In oxygen-poor soils, rhizosphere oxidation is strongly influenced by aerenchyma size and number. Seedlings may do poorly due to insufficient aerenchyma. Since large stands of Spartina have more aerenchyma, they are better able to utilize nutrients and increase productivity (Bertness 1991). Therefore, as Washington’s Spartina populations expand, they may become better able to survive at lower elevations of the intertidal zone due to increased aerenchyma.

Reproduction: Spartina alterniflora can spread by seed, rhizome, or vegetative fragmentation (Daehler and Strong 1994). However, the plant does not produce seed in several areas where it has been introduced. No flowers have been observed in New Zealand or in Padilla Bay, and the Willapa Bay population was not observed to flower for almost 50 years after its introduction (Partridge 1987; Kunz and Martz 1993; Riggs 1992; Scheffer 1945). Low soil temperature can delay or suppress flowering and reduce seed production in Spartina. Since the waters of the Washington coast are cooler than those in the species’ native range, temperature may be regulating flowering and seed set here (Ebasco Environmental 1992a). Observed increases in seed production in Willapa Bay may be linked factors that increase water temperature, such as El Nino events or sedimentation in the bay, which decreases water depth in areas, leading to increased water temperatures (Ebasco Environmental 1992a).

In Willapa Bay, the plant flowers from July to October, with seed set beginning in early September (Sayce and Mumford 1990). The species is protogynous, meaning that female flowers mature before male flowers (Bertness and Shumway 1992). This strategy helps ensure outcrossing. Experiments in San Francisco Bay indicate that self-pollinated seeds fail to germinate (Daehler and Strong 1994). Since the S. alterniflora populations on the West Coast were probably established from a relatively small number of genetic individuals, variability in reproductive output among clones may be due to inbreeding depression (Daehler and Strong 1994).

Response to Mechanical Control 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 pullings will eventually kill small plants (Spartina Task Force 1994). However, pulling or digging established clones is difficult and largely ineffectual. Findings from attempts to remove a 1 by 2 m 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).:  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 pullings will eventually kill small plants (Spartina Task Force 1994). However, pulling or digging established clones is difficult and largely ineffectual. Findings from attempts to remove a 1 by 2 m 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).