Mya arenaria

Invasion History

First Non-native North American Tidal Record: 1874
First Non-native West Coast Tidal Record: 1874
First Non-native East/Gulf Coast Tidal Record:

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General Invasion History:

Mya arenaria's current native range is from subarctic Labrador, Canada to Cape Hatteras, North Carolina and sporadically to South Carolina (Abbott 1974; Gosner 1978; Carlton 2023a). Records of M. arenaria in the Northwest Pacific, from the Yellow Sea, China to the Bering Sea (Zenekevich 1963; Golikov et al. 1976) are now referred to the very similar M. japonica, which requires genetic identification.  Two specimens of M. japonica have been identified in Haida Gwaii, British Columbia, but the extent of this species on the West Coast is unknown (Zhang et al. 2018). Based on the fossil record, Mya arenaria originated in the North Pacific Ocean, possibly around Japan, during the Miocene period and soon colonized the Atlantic, reaching the European coast in the late Pliocene, but then dying out during most of its range in the Pleistocene. In Europe, the West Coast, and Alaska, it is absent for prehistoric human shell middens, disregarding some probable misidentifications (Carlton 1979).The surviving populations were on the East Coast of North America, and the East Coast of Asia (Vermeij 1989; Strasser 1999). Mya arenaria appears to be extinct in the Arctic Ocean, though determining its present distribution is complicated by occurrence of subfossil shells and other species of Mya and related genera (Bernard 1979, James T. Carlton, personal communication). Humans have re-introduced M. arenaria to much of its former range, and beyond. Vikings may have transported this clam to Scandinavia as early as the 13th century, and later shipping and food introductions may have moved it to most of the European coast, from the Barents Sea to the Iberian Peninsula (Petersen 1992; Strasser 1999). It is also established in a few estuaries along the Mediterranean Sea (Zenetos et al. 2003) and in the Black Sea (Gomiou et al. 2002). Softshell Clams were apparently introduced to the West Coast with plantings of Eastern Oysters (Crassostrea virginica) by 1874, and were soon deliberately transplanted as food as far north as Alaska (Carlton 1979; Powers 2006). Recent genetic studies support the recent (post-Pleistocene) introduction of Mya arenaria to Europe and the West Coast of North America (Cross et al. 2016; Lasota et al. 2016).

North American Invasion History:

Invasion History on the West Coast:

Mya arenaria was first reported on the West Coast in San Francisco Bay, California in 1874 (as M. hemphilli, Newcomb 1874, cited by Carlton 1979). It rapidly became abundant and widespread in the Bay, supporting fisheries, as early as the 1880s, and spreading as far upstream as Collinsville and Sherman Lake in the Delta (Cohen and Carlton 1995). Some early introductions to other estuaries, such as Coos Bay, Oregon (OR) (~1875, Dall 1897, cited by Carlton 1979) may have also occurred with oyster plantings, but M. arenaria rapidly became a desirable food item, and was planted deliberately. Early plantings occurred in the Siuslaw River, OR; Willapa Bay, Washington (WA) (in 1884, Stearns 1885, cited by Carlton 1979); Grays Harbor, WA (in 1888, Collins 1892, cited by Palacios et al. 2000); Puget Sound, WA (in 1888, introduced from Willapa Bay, Smith 1896, cited by Carlton 1979); the San Juan Islands (Smith 1896, cited by Carlton 1979); Vancouver Island, British Columbia (BC) (Departure Bay, Strait of Georgia; Taylor 1895, cited by Carlton 1979) and Clayoquot Sound, BC (Newcomb 1893, cited by Carlton 1979). In the 20th century, government and individual plantings occurred in many smaller estuaries from California to British Columbia. In California, populations were established from Bolinas Lagoon to Humboldt Bay and Crescent City by 1920-1922, mostly by state stocking (Weymouth 1920, Bonnot 1940, cited Carlton 1979). In Oregon and Washington, first reports of established populations in smaller estuaries are often later (1917-1950s, Edmondson 1922 and Marriage 1953, cited by Carlton 1979), but this may reflect less sampling in this region.

North of Vancouver Island, BC, M. arenaria was collected in the Queen Charlotte Islands in Massett Inlet in 1939 (Carl and Guiguet 1972; Carlton 1979); Prince Rupert in 1955 (Quayle 1960, cited by Carlton 1979); and Ketchikan, Alaska (AK) in 1946 (Hanna 1966; Carlton 1979). As mentioned above, the history of M. arenaria in Alaska is complicated by the presence of subfossil shells of this species and by the occurrence of similar related species. However, excluding some dubious records, it was present at Hooper Bay, AK (61.5°N) by 1924 (Baxter, personal communication, cited by Carlton 1979), and is common in Bristol Bay (58°N) and Norton Sound (64°N) (Bernard 1979), where it may have been present by 1905. Drift shells have been reported as far north as Kotzebue Sound (67ºN; Bernard 1979). Populations are well established south of the Aleutians, in Prince William Sound (Feder and Paul 1974, cited by Carlton 1979; Powers 2006), Kachemak Bay (1999, Hines and Ruiz 2001), and Kodiak Island (Nybakken 1969, cited by Carlton 1979). These northern occurrences probably represent individual, undocumented introductions, rather than long-range larval dispersal (Carlton 1979).

While M. arenaria has been an extremely successful invader, north of San Francisco Bay, it has not become established in several locations to the south. It was introduced to Santa Cruz, California in 1881 (Stearns 1881, cited by Carlton 1979), and to Morro Bay in 1915 (Heath 1916, cited by Carlton 1979), but both stockings failed. Mya arenaria stocked in Elkhorn Slough, before 1911, may have survived for a while, but by the 1990s, it was locally extinct (Wasson et al. 2001). In San Francisco Bay (Nichols and Thompson 1985; Poulton et al. 2004), Grays Harbor, WA (Palacios et al. 2000) and probably elsewhere, the Softshell Clam has undergone great fluctuations in abundance. In South San Francisco Bay, Nichols and Thompson (1985b) considered it to be an ‘irruptive species, appearing in abundance only one year during a 10-year period’. In the upper estuary of San Francisco Bay, from San Pablo to Suisun Bays, M. arenaria shows great spatial patchiness, as well as temporal variation. During dry periods, when salinities are high, it extends its range into Suisun Bay, but disappears from the upper reaches during flood periods (Nichols and Thompson 1985a). In Grays Harbor, soon after introduction in 1895-1897, a massive population explosion took place, followed by catastrophic mortality, leaving extensive 'death assemblages' of shells (Palacios et al. 2000). In general though, M. arenaria has been notably successful in establishing populations in San Francisco Bay and northward. It is capable of surviving and reproducing at lower salinities than native West Coast bivalves and is often the dominant (or only) marine bivalve in upper estuaries. It also tends to occur higher in the intertidal zone than native clams. Consequently, its invasion success may have been due to filling an unoccupied niche (Carlton 1979).
 

Invasion History Elsewhere in the World:

Mya arenaria is present in European fossil deposits from the Pliocene, but is believed to have become extinct in the late Pliocene, and is absent from prehistoric shell middens (Strasser 1999; Behrends et al. 2005). Several specimens in a Danish sand-dune deposit were estimated to date from1245-1295 CE, using C14 dating (Petersen et al. 1992) indicating a possible introduction by Vikings returning from North America. The Softshell Clam appeared very early in Western Europe, with a report from the Netherlands in 1765 (Baster 1765, cited by Wolff 2005). Generally, from Atlantic France to the western Baltic, the date of invasion is unknown, but is believed to be between 1500 and 1700 (Strasser 1999; Goulletquer et al. 2002). Charles Lyell, examining rocks near Stockholm, Sweden, in 1834, noted that this bivalve was abundant in the Baltic, but was absent in fossils, unlike other common Baltic mollusks (Lyell 1835, cited by Munthe 1894). By 1900, it was established along the west and south coasts of Sweden (Swedish Environmental Protection Agency 2006). It is now found in the inner Baltic, including the Gulfs of Bothnia, Riga, and Finland (Strasser 1999; Leppakoski and Olenin 2000; Swedish Environmental Protection Agency 2006; Zaiko et al. 2011; Olenin and Leppakoski 2012). Mya arenaria may have been originally transported with ballast stones or as food, and after its initial introduction, was probably extensively planted as seafood (Strasser 1999). European populations show a low level of genetic diversity, and a relatively homogenous population, indicating rapid gene flow and geographical expansion (Lasota et al. 2004).

In the farther reaches of Europe, Mya arenaria was found on the east coast of Iceland in 1958 (Oskarssen 1961, cited by Strasser 1999). It is established and is absent from the fossil record on the island (Simonarson and Leifsdottir 2009). It is reported to occur all along the coast of Norway, and is abundant in the Oslofjord (Winther and Gray 1985, cited by Strasser 1985), but specific records are not available for the western and northern coast (Strasser 1985). This clam is established in the White Sea (Maximovich and Guerassimova 2003), and to the Barents Sea, east of Svyaty Nos, on the Kola Peninsula (Zenkevich 1963; Galkin 1998). It was present in the White Sea, at least as early as 1963 (Zenkevich 1963; Russanova 1963, cited by Maximovich and Guerassimova 2003).

In the southern part of its European range, M. arenaria is believed to have become established in French waters by 1700 (Goulletquer et al. 2002). However, the first definite record on the Iberian Peninsula was in the Ria de Aveiro, Portugal in 1997 (Conde et al. 2012b). An early record (1988) from the Lima estuary was a misidentification, but M. arenaria is now established in the Lima (2010) and Tagus (2007) estuaries, Portugal (Conde et al. 2009; Conde 2012a). The distribution of the Softshell Clam in the Mediterranean Sea is spotty. Established populations were discovered in two French lagoons, Berre and Vaine in 1976 (Zenetos et al. 2003), and in the Gulf of Saronicos, Greece, in 1984 (Zenetos et al. 2005). Isolated collections were made in Sicily and the Adriatic (Zenetos et al. 2003; not established, Occhipinti-Ambrogi et al. 2011). Mya arenaria was found in the Black Sea in Romania in 1966, and became abundant enough to be regarded as a pest (Gomiou et al. 2002, Skolka and Preda 2010). It has spread to the Sea of Marmara (in 1996, Albayrak and Balcis 1996, cited by Albayrak 2011), and to the Sea of Azov (Savchuck 1980, cited by Zaitsev and Ozturk 2001).

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Description

Mya arenaria is a bivalve with a thin, elongate, elliptical shell, gaping at the anterior and posterior ends even when closed. The pallial sinus is deep and somewhat V-shaped. The hinge is asymmetrical, with a long, tongue-shaped chondrophore in the left valve, and a heart-shaped pit on the right. The shell is chalky white with a thin dull-brown or yellowish periostracum. The typical maximum size is 75-100 mm, with a record length of 163 mm. It usually borrows in soft muddy to sandy sediments in shallow waters and intertidal mud flats (Abbott 1974; Gosner 1978; Coan et al. 2000; Coan and Valentich-Scott 2007). In large specimens, the siphon may extend for as much as 200 mm to reach the surface (Newell and Hidu 1986).

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Taxonomy

Ecology

General:

Mya arenaria is a large bivalve which inhabits gravelly to muddy bottoms, from the mid-intertidal to about 100 m depth, though they are rare below 9-10 m. In regions with large tidal ranges, they are most-abundant in intertidal mudflats (Gosner 1978; Newell and Hidu 1986). They require temperatures above 12-15°C for spawning, but do not tolerate temperatures above 28°C for prolonged periods (Newell and Hidu 1986). Mya arenaria is unusually tolerant of low salinities, and can be acclimated to feed at 3 PSU (Castagna and Chanley 1973). In estuaries such as Chesapeake Bay and brackish seas such as the Baltic, Softshell Clams can be abundant at salinities as low as 4-5 PSU, while at marine salinities (25-25 PSU), predation may reduce their abundance in subtidal waters (Newell and Hidu 1986; Carlton 1979). Sexes are usually separate, but there is a low incidence of hermaphroditism. Size appears more important than age in determining maturity. Maturity occurs at about 20 mm length, while market size is about 50 mm. Market size is reached in about 1.5 years in Connecticut, 3-6 years in Maine, 5 years in New Brunswick and the White Sea (Sadykhova 1979; Newell and Hidu 1986).

Mya arenaria usually spawns twice a year in spring and fall, mostly in the southern part of its range (Connecticut, Rhode Island, but also in Oslofjord, Norway and southern England), but once a year mostly further north (White Sea- Russia, Maine, New Brunswick, Ireland, Sweden, Wadden Sea, but also the Black Sea) Spawning usually occurs at 10-25ºC, but the temperature range is quite variable (Sadykhova 1979; Newell and Hidu 1986; Strasser 1999; Cross et al. 2012). Reported fecundity ranges from about 100,000 to 3 million eggs (Newell and Hidu 1986). The eggs and sperm are released through the exhaling siphon. Fertilized eggs develop into trochophore larvae within 9 hours and a few hours later they grow their first shell (called 'D-shaped', or 'straight-hinged). The larvae swim and feed on phytoplankton, using a ciliated velum. At about 12-20 days, and 175-230 μm, they develop a ciliated foot, and begin to investigate substrates for settlement (Chanley and Andrews 1971; Newell and Hidu 1986). At the end of this pediveliger stage, the velum is lost and the larvae settle, moving by crawling, and attaching to grains of sand or sediment, seaweeds or surfaces, using byssal threads. As the clams grow, they burrow deeper, the siphons elongate, and the byssus glands atrophy. At about 5 mm size, clams are called 'seed'. As they grow, they tend to move shoreward (Newell and Hidu 1986). Mortality is very high for larvae and seed clams, but once clams reach adult size, a life span of 10 years is typical, with some specimens living for 20 years (Strasser 1999).

Softshell clams are suspension feeders and can burrow up to 20 cm (in large specimens), with their siphon protruding above the surface. They draw water through the incurrent siphon, to the gills, where food particles are trapped in mucus and carried by cilia to the mouth to be ingested. Particles which are too large or inedible, or simply too dense for ingestion, are rejected by the labial palps as pseudofeces. Diatoms and flagellates are optimal food, but clams can obtain some nutrition from suspended detritus. Feeding rates are influenced by temperature, salinity, and food quality. Filtration and assimilation drops to very low levels below 3ºC. These clams are able to feed in water with considerable quantities of suspended silt and are able to sort cells for silt particles before ingestion (Newell and Hidu 1986). Larvae and newly settled spat are very vulnerable to predation. Small clams are eaten by fishes, crabs, clam worms (Nereidae), moon snails (Naticidae), birds, etc. When clams reach ~60 mm in length, they are less vulnerable to predation (Newell and Hidu 1986).

Food:

Phytoplankton

Consumers:

crabs, fishes, birds, humans

Trophic Status:

Suspension Feeder

SusFed

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Habitats

General Habitat	Grass Bed	None
General Habitat	Unstructured Bottom	None
General Habitat	Oyster Reef	None
General Habitat	Salt-brackish marsh	None
Salinity Range	Mesohaline	5-18 PSU
Salinity Range	Polyhaline	18-30 PSU
Salinity Range	Euhaline	30-40 PSU
Tidal Range	Subtidal	None
Tidal Range	Low Intertidal	None
Tidal Range	Mid Intertidal	None
Vertical Habitat	Endobenthic	None

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Life History

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Tolerances and Life History Parameters

Minimum Temperature (ºC)	0	Based on range (Abbott 1974).
Maximum Temperature (ºC)	32.5	Experimental, 24 hr LC 50 (Kennedy and Mihursky 1971).
Minimum Salinity (‰)	3	Experimental, acclimation (Castagna and Chanley 1973)
Maximum Salinity (‰)	35	Based on field occurences (Castagna and Chanley 1973)
Minimum Reproductive Temperature	4	Season and temperature of spawning is highly variable- a Massachusetts population spawned at 4-6 C (Brousseau 1979, cited by Strasser 1999), while larvae in the laboratory developed poorly below 8 C (Stickney 1979, cited by Strasser 1999).
Maximum Reproductive Temperature	23	Upper limit for optimal development in the laboratory (Stickney 1964, cited by Strasser 1999).
Minimum Reproductive Salinity	10	Stickney (1965), cited by Castagna and Chanley (1973)
Maximum Reproductive Salinity	35	Stickney (1965), cited by Castagna and Chanley (1973)
Minimum Duration	10	Larval duration, laboratory- Loosanoff and Davies 1963, cited by Strasser 1999
Maximum Duration	35	Larval duration, laboratory- Loosanoff and Davies 1963, cited by Strasser 1999
Minimum Length (mm)	20	Minimum size at first sexual maturity (Newell and Hidu 1986)
Maximum Length (mm)	163	But more usually, up to 100 mm (Abbott 1974; Gosner 1978)
Broad Temperature Range	None	Polar-Warm temperate
Broad Salinity Range	None	Mesohaline-Euhaline

General Impacts

Mya arenaria is an important shellfish species in its native range, from Atlantic Canada to Chesapeake Bay, supporting both commercial and recreational fisheries. On the West Coast of the US, it supported commercial fisheries in San Francisco Bay and elsewhere historically, but is now mainly taken by recreational clammers (Cohen and Carlton 1995). Surprisingly, it is apparently rarely eaten in Europe, and may be more frequently used as bait (Eno et al. 1997; Strasser 1999). Where it is abundant, it is an important suspension-feeder, grazing phytoplankton, and an important food item for fishes, invertebrates, and birds (Nichols and Thompson 1985a; Zaiko et al. 2011) It is also a potential competitor with native bivalves (Moller 1986; Conde et al. 2011).

Economic Impacts

Fisheries- Mya arenaria is an important commercial fisheries species, eaten steamed or fried in eastern North America. Intertidal populations in New England and the Maritimes are harvested with rakes, forks, or hoes, while subtidal populations in Chesapeake and Delaware Bays are taken with hydraulic dredges (Newell and Hidu 1986). In San Francisco Bay, they supported a commercial fishery from the 1880s to 1948, but the fishery steadily declined by 1926 and ended by 1948 (Cohen and Carlton 1995). Elsewhere on the West Coast, the fishery has been mostly recreational, as indicated by state agency websites. Native clams and the Japanese Littleneck (Venerupis philippinarum) are often preferred to Softshell Clams. However, at least one culture operation is taking place in Skagit Bay, WA (Washington Department of Fish and Wildlife 2012, http://wdfw.wa.gov/fishing/shellfish/clams/eastern_softshell.html). In Europe, it is not frequently eaten, and does not support commercial fisheries. Web searches for it under the English name 'Sand Gaper' and 'fisheries', 'fishing', etc., turned up only references to using it as bait on a recreational basis (e.g., http://www.ukmarinesac.org.uk/activities/bait-collection/bc1_1.htm). In the Black Sea, it became very abundant about 4-5 years after its original discovery. When large masses of clams washed ashore, they were fed to chickens (Gomiou et al. 2002). Similarly, in the Sea of Marmars, Turkey, it is of 'no commercial importance', except as a food for larger fishes (Ozturk 2002).

Aesthetic- Soon after its invasion in the Black Sea, by the 1970s, masses of decaying M. arenaria began washing ashore, attracting masses of seagulls (Gomiou et al. 2002). Mass early occurrences and mortalities are also known from Grays Harbor, WA in the late 1800s, though aesthetic impacts were not reported (Palacios et al. 2000).

Ecological Impacts

Herbivory- When abundant, Mya arenaria is a significant herbivore in estuaries, because of its large size and powerful filtration, and its ability to survive in low salinities and wide tidal ranges, where large native bivalves are often rare. Estimated feeding rates of M. arenaria in the southwestern Baltic Sea, off Germany, indicate that this clam can filter the entire water column once or several times a day, depending on water depth (Forster and Zettler 2004). Large biomasses in San Francisco Bay (Nichols and Thompson 1985a; Nichols and Thompson 1985b), the Skagerrak (Moller 1986), the Baltic (Bubinas and Vaitonis 2003; Forster and Zettler 2004; Obolewski and Piesik 2005; Zaiko et al. 2011), and Black Sea (Gomiou et al. 2002) imply significant feeding rates.

Competition- Introduced populations of Mya arenaria in several locations are believed to have reduced or partially replaced native bivalves, including Macoma nasuta (Bent-Nose Macoma) in San Francisco Bay (Cohen and Carlton 1995), Macoma balthica in the Baltic Sea (Obolewski and Piesik 2005), Lentidium mediterraneum in the Black Sea (Skolka and Preda 2010), and Cerastoderma edule (Edible Cockle) in the Skagerrak, Sweden (Moller 1986). In the case of C. edule, competition was reciprocal, with one species or the other having heavy recruitment in some years, and inhibiting recruitment of the other (Moller 1986).

Food/Prey- Mya arenaria, when abundant, has been an important prey organism for clam worms (Nereidae), predatory snails, shrimps, crabs, fishes, ducks, and shorebirds in invaded regions (Carlton 1979; Sadykhova 1979; Ozturk 2002; Bubinas and Vaitonis 2003; Cloern et al. 2007; Skolka and Preda 2010). Because it tolerates low salinities and wide tidal ranges better than many native clams, it has the potential to increase the food supply for predators in estuaries.

Habitat Change- Mya arenaria, as a powerful burrower and filterer, has the potential to alter habitats and sediment characteristics through bioturbation and deposition of peudofeces and also through suspension feeding, increasing water clarity, and light penetration (Obolewski and Piesik 2005; Queiros et al. 2011; Zaiko et al. 2011). Introduced populations of Mya arenaria have often gone through boom-and bust phases, leaving 'death assemblages' of empty shells, providing habitat for many other benthic organisms (Strasser 1999; Palacios et al. 2000).

Trophic Cascade- During periods of exceptional abundance, Mya arenaria may have effects throughout the food web, affecting phytoplankton abundance, and in turn, zooplankton, mysids, and fish recruitment. This may have happened in 1976-1977 in Suisun Bay, California (Nichols and Thompson 1985b; Cohen and Carlton 1995). High abundances of Mya arenaria during 'boom' periods, or its empty shells during 'busts,' can affect the abundance of predators with implications for other benthic organisms. For example, high abundances of M. arenaria shells supported elevated abundances of juvenile Dungeness Crabs (Metacarcinus magister) in Grays Harbor, WA which could lead to increased predation on other benthic organisms (Palacios et al. 2000).

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Regional Impacts

NEA-II	None		Ecological Impact	Habitat Change
In Poole Harbour, England, Mya arenaria, was the most important species contributing to bioturbation of sediments (Queiros et al. 2011).
MED-IX	None		Ecological Impact	Competition
'Mya arenaria, became a dominant species on sandy bottoms, inducing structural changes in native associations previously dominated by the bivalve Lentidium mediterraneum (Costa, 1829)' (Skolka and Preda 2010).
MED-IX	None		Ecological Impact	Food/Prey
'Since the tiny Lentidium mediterraneum is a food resource for the juveniles of many native bottom fish species while the juveniles of Mya arenaria are consumed by the adults of the same' (Skolka and Preda 2010).
B-VII	None		Ecological Impact	Competition
Some community impacts (Zaiko et al. 2011). Off the Pomeranian coast of Poland, Mya arenaria and Macoma balthica often have an inverse relationship, suggestive of competition (Obolewski and Piesik 2005).
B-VII	None		Ecological Impact	Habitat Change
Some habitat impacts (Zaiko et al. 2011). Mya arenaria can alter sediment characteristics through bioturbation and deposition of pseudofeces (Obolewski and Piesik 2005).
B-VIII	None		Ecological Impact	Competition
Some community impacts (Zaiko et al. 2011)
B-VII	None		Ecological Impact	Food/Prey
Mya arenaria is a frequent food of European Flounder (Platichthys flesus) in the Baltic, off Lithuania (Bubinas and Vaitonis 2003), and of several flounder species off the Pomeranian coast of Poland (Obolewski and Piesik 2005).
NEP-V	Northern California to Mid Channel Islands		Economic Impact	Fisheries
By the 1880s, M. arenaria supported a commercial fishery of 500-900 tons per year in San Francisco Bay, but this declined to 100 tons per year by 1916 to 1926, and ended after 1948, due to overharvesting, pollution, and possible preference for Venerupis phillipinarum (Japanese Littleneck). However, recreational harvests continue to the present (Cohen and Carlton 1995). Extensive plantings were carried out along the California coast by individuals and the California Department of Fish and Game (Weymouth 1920; Bonnot 1940, both cited by Carlton 1979). Recreational clamming probably occurs in many other estuaries where clams are common.
NEP-V	Northern California to Mid Channel Islands		Ecological Impact	Competition
Mya arenaria may have replaced Macoma nasuta in clam beds in San Francisco Bay (Cohen and Carlton 1995).
P090	San Francisco Bay		Economic Impact	Fisheries
By the 1880s, M. arenaria supported a commercial fishery of 500-900 tons per year in San Francisco Bay, but this declined to 100 tons per year by 1916 to 1926, and ended after 1948, due to overharvesting, pollution, and possible preference for Venerupis phillipinarum (Japanese Littleneck). However, recreational harvests continue to the present (Cohen and Carlton 1995).
NEP-V	Northern California to Mid Channel Islands		Ecological Impact	Herbivory
Mya arenaria, when abundant, has had significant impact as a filter-feeder. During periods of high salinity, it has been one of several filter-feeders contributing to low phytoplankton biomass in Suisun Bay (Nichols and Thompson 1985a).
NEP-V	Northern California to Mid Channel Islands		Ecological Impact	Food/Prey
Mya arenaria is an important prey organism for ducks, shorebirds, flounders, skates, rays, and native crabs and shrimps (Carlton 1979; Cloern et al. 2007).
P090	San Francisco Bay		Ecological Impact	Competition
Mya arenaria may have replaced Macoma nasuta in clam beds in San Francisco Bay (Cohen and Carlton 1995).
P090	San Francisco Bay		Ecological Impact	Herbivory
Mya arenaria, when abundant, has had significant impact as a filter-feeder. During periods of high salinity in 1976-1977, it has been one of several filter-feeders contributing to low phytoplankton biomass in Suisun Bay (Nichols and Thompson 1985a).
P090	San Francisco Bay		Ecological Impact	Food/Prey
Mya arenaria is an important prey organism for ducks, shorebirds, flounders, skates, rays, and native crabs and shrimps (Carlton 1979; Cloern et al. 2007).
NEP-IV	Puget Sound to Northern California		Economic Impact	Fisheries
In Humboldt Bay. 'It is taken for bait and food by sport clammers.' (Boyd et al. 2002). Recreational clamming for M. arenaria is also popular in Oregon. According to the Oregon Division of Fish and Wildlife, this clam is present in nearly every Oregon estuary (http://www.dfw.state.or.us/mrp/shellfish/bayclams/dig_softshell.asp). In Washington, they are less popular than Butter Clams (Saxidomus gigantea) or Littlenecks (Leukoma staminea- Pacific Littleneck; Venerupis philippinarum- Japanese Littleneck) (Washington Department of Fish and Wildlife 2012, http://wdfw.wa.gov/fishing/shellfish/clams/eastern_softshell.html).
NEP-III	Alaskan panhandle to N. of Puget Sound		Economic Impact	Fisheries
In Washington, they are less popular than Butter Clams (Saxidomus gigantea) or Littlenecks (Leukoma staminea- Pacific Littleneck; Venerupis philippinarum- Japanese Littleneck). However, commercial culture is taking place on private grounds in Skagit Bay and Port Susan (Washington Department of Fish and Wildlife 2012, http://wdfw.wa.gov/fishing/shellfish/clams/eastern_softshell.html). In British Columbia, they are occasionally harvested recreationally, but fisheries are often closed due to red tides (British Columbia Provincial Government, http://www.shim.bc.ca/species/softshel.htm).
P290	Puget Sound		Economic Impact	Fisheries
According to the Oregon Division of Fish and Wildlife, this clam is present in nearly every Oregon estuary (http://www.dfw.state.or.us/mrp/shellfish/bayclams/dig_softshell.asp). In Washington, they are less popular than Butter Clams (Saxidomus giganteus) or Littlenecks (Leukoma staminea- Pacific Littleneck; Venerupis philippinarum- Japanese Littleneck). However, commercial culture is taking place on private grounds in Skagit Bay and Port Susan (Washington Department of Fish and Wildlife 2012, http://wdfw.wa.gov/fishing/shellfish/clams/eastern_softshell.html).
B-I	None		Ecological Impact	Competition
In the Gulmarfjord, Sweden, high densities of adult M. arenaria inhibited recruitment of spat of both Cerastoderma edule and M. arenaria . However, in some years, heavy recruitment of C. edule could inhibit M. arenaria recruitment (Moller 1986).
MED-IX	None		Economic Impact	Aesthetic
By the 1970s, 4-5 years after its initial discovery in the Black Sea, Mya arenaria became so abundant that it washed ashore in decaying masses, attracting huge flocks of seagulls (Gomiou et al. 2002).
MED-IX	None		Economic Impact	Fisheries
During mass occurrences in the 1970s, Mya arenaria was fed to chickens (Gomiou et al. 2002).
MED-VIII	None		Ecological Impact	Food/Prey
Mya arenaria in the Sea of Marmara is eaten by Rapana venosa (Veined Rapa Whelk), and by fishes, including sturgeons, Turbot (Scophthalmus maximus), mullets, and gobies (Ozturk 2002).
B-VII	None		Ecological Impact	Herbivory
Inferred from large reported biomasses (Bubinas and Vaitonis 2003) and the reporting of 'some ecosystem impacts' (Zaiko et al. 2011).
AR-III	None		Ecological Impact	Food/Prey
In Kandalaksha Bay, White Sea, Russia, the most frequent predators of Mya arenaria are sandpipers (Sadykhova 1979).
P090	San Francisco Bay		Ecological Impact	Trophic Cascade
During a drought in 1976-1977 in Suisun Bay, a high abundance of Mya arenaria and other marine filter-feeders may have contributed to a low phytoplankton abundance, which in turn contributed to low zooplankton abundance and a scarcity of the omnivorous Neomysis mercedis, an important food for juvenile fishes. This, in turn, may have led to decreased recruitment of Morone saxatilis (Striped Bass), an economically important introduced gamefish (Nichols and Thompson 1985b; Cohen and Carlton 1995).
NEP-V	Northern California to Mid Channel Islands		Ecological Impact	Trophic Cascade
During a drought in 1976-1977 in Suisun Bay, a high abundance of Mya arenaria and other marine filter-feeders may have contributed to a low phytoplankton abundance, which in turn contributed to low zooplankton abundance and a scarcity of the omnivorous Neomysis mercedis, an important food for juvenile fishes. This, in turn, may have led to decreased recruitment of Morone saxatilis (Striped Bass), an economically important introduced gamefish (Nichols and Thompson 1985b; Cohen and Carlton 1995).
NEP-IV	Puget Sound to Northern California		Ecological Impact	Habitat Change
In Grays Harbor WA, large shell deposits provide a highly favorable habitat for settling Dungeness Crab (Metacarcinus magister) juveniles. High densities of these crabs may, in turn, limit the recruitment of M. arenaria).
P280	Grays Harbor		Ecological Impact	Habitat Change
In Grays Harbor WA, large shell deposits provide a highly favorable habitat for settling Dungeness Crab (Metacarcinus magister) juveniles. High densities of these crabs may, in turn, limit the recruitment of M. arenaria.
B-III	None		Ecological Impact	Herbivory
Estimated filtration rates of Mya arenaria populations in the southwestern Baltic Sea, Germany, at 0.5-9 m depth indicate that that this clam can filter the entire water column in one day or less (Forster and Zettler 2004).
CA	California		Ecological Impact	Competition
Mya arenaria may have replaced Macoma nasuta in clam beds in San Francisco Bay (Cohen and Carlton 1995)., Mya arenaria may have replaced Macoma nasuta in clam beds in San Francisco Bay (Cohen and Carlton 1995).
CA	California		Ecological Impact	Food/Prey
Mya arenaria is an important prey organism for ducks, shorebirds, flounders, skates, rays, and native crabs and shrimps (Carlton 1979; Cloern et al. 2007)., Mya arenaria is an important prey organism for ducks, shorebirds, flounders, skates, rays, and native crabs and shrimps (Carlton 1979; Cloern et al. 2007).
CA	California		Ecological Impact	Herbivory
Mya arenaria, when abundant, has had significant impact as a filter-feeder. During periods of high salinity, it has been one of several filter-feeders contributing to low phytoplankton biomass in Suisun Bay (Nichols and Thompson 1985a)., Mya arenaria, when abundant, has had significant impact as a filter-feeder. During periods of high salinity in 1976-1977, it has been one of several filter-feeders contributing to low phytoplankton biomass in Suisun Bay (Nichols and Thompson 1985a).
CA	California		Ecological Impact	Trophic Cascade
During a drought in 1976-1977 in Suisun Bay, a high abundance of Mya arenaria and other marine filter-feeders may have contributed to a low phytoplankton abundance, which in turn contributed to low zooplankton abundance and a scarcity of the omnivorous Neomysis mercedis, an important food for juvenile fishes. This, in turn, may have led to decreased recruitment of Morone saxatilis (Striped Bass), an economically important introduced gamefish (Nichols and Thompson 1985b; Cohen and Carlton 1995)., During a drought in 1976-1977 in Suisun Bay, a high abundance of Mya arenaria and other marine filter-feeders may have contributed to a low phytoplankton abundance, which in turn contributed to low zooplankton abundance and a scarcity of the omnivorous Neomysis mercedis, an important food for juvenile fishes. This, in turn, may have led to decreased recruitment of Morone saxatilis (Striped Bass), an economically important introduced gamefish (Nichols and Thompson 1985b; Cohen and Carlton 1995).
CA	California		Economic Impact	Fisheries
By the 1880s, M. arenaria supported a commercial fishery of 500-900 tons per year in San Francisco Bay, but this declined to 100 tons per year by 1916 to 1926, and ended after 1948, due to overharvesting, pollution, and possible preference for Venerupis phillipinarum (Japanese Littleneck). However, recreational harvests continue to the present (Cohen and Carlton 1995). Extensive plantings were carried out along the California coast by individuals and the California Department of Fish and Game (Weymouth 1920; Bonnot 1940, both cited by Carlton 1979). Recreational clamming probably occurs in many other estuaries where clams are common., By the 1880s, M. arenaria supported a commercial fishery of 500-900 tons per year in San Francisco Bay, but this declined to 100 tons per year by 1916 to 1926, and ended after 1948, due to overharvesting, pollution, and possible preference for Venerupis phillipinarum (Japanese Littleneck). However, recreational harvests continue to the present (Cohen and Carlton 1995).
WA	Washington		Ecological Impact	Habitat Change
In Grays Harbor WA, large shell deposits provide a highly favorable habitat for settling Dungeness Crab (Metacarcinus magister) juveniles. High densities of these crabs may, in turn, limit the recruitment of M. arenaria.
WA	Washington		Economic Impact	Fisheries
According to the Oregon Division of Fish and Wildlife, this clam is present in nearly every Oregon estuary (http://www.dfw.state.or.us/mrp/shellfish/bayclams/dig_softshell.asp). In Washington, they are less popular than Butter Clams (Saxidomus giganteus) or Littlenecks (Leukoma staminea- Pacific Littleneck; Venerupis philippinarum- Japanese Littleneck). However, commercial culture is taking place on private grounds in Skagit Bay and Port Susan (Washington Department of Fish and Wildlife 2012, http://wdfw.wa.gov/fishing/shellfish/clams/eastern_softshell.html).
OR	Oregon		Economic Impact	Fisheries
According to the Oregon Division of Fish and Wildlife, this clam is present in nearly every Oregon estuary (http://www.dfw.state.or.us/mrp/shellfish/bayclams/dig_softshell.asp

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