Ruditapes philippinarum

Invasion History

First Non-native North American Tidal Record: 1924
First Non-native West Coast Tidal Record: 1924
First Non-native East/Gulf Coast Tidal Record:

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General Invasion History:

Venerupis philippinarum has a wide native range, from the southern Kuril and Sakhalin Islands, Russia (Golikov et al. 1976) to India, Sri Lanka, and the Philippines (Huang 2001; Academy of Natural Sciences of Philadelphia 2006; Mao et al. 2011). It was introduced to Hawaii as a food animal in 1918 (Carlton and Eldredge 2009), but reached the West Coast of North America (Samish Bay, Washington) with plantings of Pacific Oysters (Crassostrea gigas) (Carlton 1979), and was then widely introduced from British Columbia to California as a popular seafood item (Carl and Giguet 1972; Cohen and Carlton 1995). It was introduced to northern France in 1974, and is established from Ireland and the Netherlands, to Spain, Greece, and Turkey (Cigarria et al. 1997; Goulletquer et al. 2002; Zenetos et al. 2002; Drummond et al. 2006). It is now widely and often intensively farmed, as well as being recreationally harvested, in its native and introduced range (Food and Agricultural Organization 2013).

North American Invasion History:

Invasion History on the West Coast:

Venerupis philippinarum was first reported in the Northeastern Pacific in Samish Bay, Washington (WA) in 1924, in areas where Pacific Oysters had been planted (Kincaid 1947, cited by Carlton 1979). It began to spread along the coast to the north and south, reaching Ladysmith, on the east coast of Vancouver Island, British Columbia by 1936, and spreading up the Strait of Georgia in the 1940s and 1950s. The Japanese Littleneck also spread up the west coast of Vancouver Island, colonizing Barkley Sound and Esperanza Inlet in the 1950s, reaching Quatsino Island near the north end of the island before 1971 (Carl and Guiguet 1972; Carlton 1979). In 1972, it was found on Spider Island, in southern Queen Charlotte Sound (Carlton 1979, 50°50'N). In a 2006 survey, it was found at Princess Royal Island, further north in Queen Charlotte Sound (53°N, Gillespie et al. 2007), its current northern limit. This spread appears to be mostly due to the movement of planktonic larvae by currents, but aided also by oyster plantings.

To the south, V. philippinarum was reported in Puget Sound in 1943 (Eyerdam 1943, cited by Carlton 1979; Cohen et al. 1998), Willapa Bay in 1947, and San Francisco Bay in 1947 (Carlton 1979; Cohen and Carlton 1995). It was discovered later at several intermediate sites, including the San Juan Islands in 1950, Grays Harbor in 1964, and Humboldt Bay in 1964. These records may not represent dispersal, but instead recognition of clams introduced with earlier plantings of Pacific Oysters (Carlton 1979). Venerupis philippinarum may have been easily overlooked, owing to its similarity to the native Pacific Littleneck (Leukoma staminea) (Abbott 1974; Cohen 2005; Coan and Valentich-Scott, in Carlton 2007). Once this clam was recognized as a desirable shellfish, state fish and game agencies, and probably private individuals, as well, began stocking it in West Coast estuaries. Stocking attempts occurred in Oregon at Netarts, Tillamook, Yaquina, and Coos Bays, but established populations occur only in Netarts Bay (Carlton 1979; Carlton 1989; Wonham and Carlton 2005). In smaller estuaries in California, including Bodega Harbor, Estero Americano, and Elkhorn Slough, V. philippinarum was discovered between 1949 and 1977, probably spreading with oyster transplants, natural dispersal, and possibly unofficial plantings. Deliberate plantings were made by the California Fish and Game Department in Morro Bay, Newport Bay, and the Salton Sea (a desert salt lake) from 1953 to 1967, but these were all unsuccessful (Carlton 1979). However, in 1998 and 2000 surveys, V. philippinarum was found in several southern California estuaries, including Port Hueneme, Los Angeles-Long Beach Harbors, and Newport Bay (Fairey et al. 2002; Ranasinghe et al. 2005). In 2009, it was the dominant bivalve in Colorado Lagoon, a small estuary in Long Beach, CA (Burnaford et al. 2011). By 2013, it was abundant in Mission Bay, San Diego (Talley et al. 2015). The Japanese Littleneck was reported in Bahía de San Quintín, Baja California, Mexico in 1987 (Cohen 2005).

Invasion History in Hawaii:

Venerupis philippinarum may have been introduced in Pearl Harbor by a Japanese immigrant in the 1880s or 1890s, but the first documented collections were made in 1918 (Carlton and Eldredge 2009). In 1920 it was introduced to Kaneohe Bay and Kahili Basin (Yap 1977; Coles et al. 2002; Carlton and Eldredge 2009). It was later introduced to Molokai, Kauai; Maui; Lanai; and Hawaii (Brock 1960; Carlton and Eldredge 2009). Some of these populations have been eliminated, reduced, or restricted by heavy human harvesting and native predators (Carlton and Eldredge 2009).

Invasion History Elsewhere in the World:

In Europe, several batches of 400 to 500,000 V. philippinarum from Puget Sound were imported into France under supervision by the Institute Scientifique des Peches Maritimes in 1972. They were raised, bred, and released in 1973-1974 to waters in Normandy, along the English Channel (Flaasch and Leborgne 1992; Goulletquer et al. 2002). The success of these introductions, led to culture and planting of these 'Manila Clams' in British waters, beginning in 1980. Initially, it was believed that there would be no recruitment in UK waters, due to low water temperatures (Utting and Spencer 1992). However, a population introduced in Poole Harbour, off the English Channel, in 1988, became established (Jensen et al. 2004; Humphreys et al. 2007; Herbert et al. 2012). On the west coast of Ireland and southern Norway, the clam is cultured, but successful recruitment has not been observed (Mortensen et al. 2000; Drummond et al. 2006). As a result of successful cultivation and establishment of V. philippinarum in northern France, by the 1980s, it was introduced in Atlantic Spain (Cigarria et al. 1997), and in the Thau Lagoon, on the Mediterranean coast of France (Zenetos et al. 2003). In 1983, cultivation began in the Lagoon of Venice and soon the lagoons of the northern Adriatic became the dominant region for commercial production of the bivalve (Breber 2002; Crocetta 2012; Sladonja et al. 2011). It is also established in the Sea of Marmara, Turkey, the adjacent Aegean Sea (Cinar et al. 2005; Albayrak 2011), and lagoons on the Tyrrhenian and Ionian coasts of Italy (Crocetta 2012).

Venerupis philippinarum has been introduced to Tahiti and Fiji (Eldredge 1994; US National Museum of Natural History 2007), but the success of these introductions is not known.

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Description

Ruditapes philippinarum ias been known, especially in North America, as Venerupis philippinarum, and frequently by the older names Tapes philippinarum, or Tapes japonica. This clam's shape is roughly oval, with a moderate beak located anterior of the midline. The exterior of the shell is sculptured with concentric lines and radial ribs, with beadlike nodes at their intersections. The ribs are somewhat stronger in the center of the shell. The inner ventral margin is smooth. The hinges of the two valves are very similar. The ligament is elevated above the dorsal margin. The lunule is heart-shaped. The two siphons are separate at the tips. The color of the shell is highly variable, but the shell is often predominantly cream-colored or gray. It is often variegated, with concentric brown lines, or angular patches. Specimens from anoxic mud are sometimes completely black. The interior margins are deep purple, while the center of the shell is pearly white, and smooth. The pallial sinus is often stained with yellow. The clam reaches 40 to 57 mm in length and in rare instances to 79 mm. Description from: Abbott 1974; Cohen 2005; Coan et al. 2000; Coan and Valentich-Scott, in Carlton 2007; Gillespie et al. 2012.

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Taxonomy

Ecology

General:

Ruditapes philippinarum is a burrowing bivalve, most abundant in shallow, subtropical to cool-temperate areas, in coarse sand and gravel. The sexes are separate. The clams can mature at sizes as small as 15 mm, especially in warmer climates (southern Japan, Hawaii) where they can spawn in their first year, but in cooler locations (northern Japan, Pacific Russia, Puget Sound) they begin spawning at 2 to 3 years of age at 22-35 mm (Yap 1977; Ponurovsky and Yakolev 1992). Spawning occurred year-round in Hawaii (Yap 1977), but was limited to 1 or 2 summer months in northern locations (Ponurovsky and Yakolev 1992). The minimum spawning temperature is around 12°C, but the optimal range is 20-22°C, although larval development can take place at 27-30°C (Toba et al. 1992, cited by Inoue et al. 2012). Fecundity of this bivalve increases with size, with 40 mm-long females producing about 1.5 - 2.4 million eggs (Yap 1977; Ponurovsky and Yakolev 1992). The eggs hatch into trochophore larvae, and within 2 days of hatching, develop a D-shaped shell. By 12-24 days, the larvae settle and attach to a shell or other hard surface with byssus threads, and soon move into the sediment (Toba et al. 1992, cited by Inoue et al. 2012).

Ruditapes philippinarum is most abundant in lower intertidal and shallow subtidal waters, often in estuaries and lagoons. Adult animals tolerate a wide range of salinities and temperatures from 12-50 PSU and 0-37°C, surviving under ice cover at the northern edge of their range (Breber 2002; Elston et al. 2003; Komorita et al. 2009; Kamenev and Nekrasov 2012). The range of salinity and temperature for reproduction is narrower, 24-35 PSU and 18-30°C (Toba et al. 1992, cited by Inoue et al. 2012; Food and Agricultural Organization 2013). In estuaries on the Pacific coast of Russia, the maximum longevity, estimated from shell rings, varied from 2 to 13 years (Ponurovsky and Yakolev 1992).

The Japanese Littleneck is a filter-feeder, taking in suspended particles through its incurrent siphon and trapping them on its gills. While larvae and juveniles feed mostly on phytoplankton, the adults in some locations may feed more heavily on benthic microalgae, primarily pennate diatoms, in the bottom surface film (Breber 2002). In the Fraser River Delta, isotopic measurements of V. philippinarum showed that they appear to be getting most of their nutrition from particulate organic matter (Sakamaki and Richardson 2008; Dias et al. 2019). At a site in Japan, terrestrial organic matter apparently makes only a minor contribution to their nutrition (Kasai et al. 2004). These somewhat contradictory results are suggestive of opportunistic feeding, varying with environmental conditions.

As a relatively large, but shallowly burrowing bivalve, R. philippinarum is a major prey item for native predators, such as moon snails, starfish, crabs, fishes, diving ducks, shorebirds, sea otters, and raccoons (Cohen 2005; Dudas et al. 2006; Cloern et al. 2007; Lewis et al. 2007; Gillespie et al. 2012). The introduced Green Crab (Carcinus maenas) is also a significant predator (Grosholz et al. 2001). This bivalve also supports numerous parasites, including a variety of bacteria, protozoans, trematodes, and the introduced parasitic copepod Mytilicola orientalis (Boweret al. 1992; Marshall et al. 2003; Gillespie et al. 2012). In Asian and European populations, protozoans of the genus Perkinsus cause significant mortality of R. philippinarum. These parasites have not yet been found on the Pacific coast of North America (Cigarria et al. 1997; Elston et al. 2003; Dungan and Reece 2006).

Food:

Phytoplankton

Trophic Status:

Suspension Feeder

SusFed

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Habitats

General Habitat	Unstructured Bottom	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
Vertical Habitat	Endobenthic	None

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Tolerances and Life History Parameters

Minimum Temperature (ºC)	0	Survives under ice cover in the Amur estuary (Kamenev, and Nekrasov 2012)
Maximum Temperature (ºC)	37	Experimental, acclimated at 25 C (Shin et al. 2000)
Minimum Salinity (‰)	12.5	Experimental (Elston et al. 2003). But survival decreases below 19.2 PSU at 18 and 24.5 C (Shin et al. 2000; Carregosa et al. 2014)
Maximum Salinity (‰)	50	In Italian lagoons (Breber 2002; Carregosa et al. 2014)
Minimum Reproductive Temperature	18	Lowest temperature for larval development (Toba et al. 1992, cited by Inoue et al. 2012)
Maximum Reproductive Temperature	30	Highest temperature for spawning (Toba et al. 1992, cited by Inoue et al. 2012)
Minimum Reproductive Salinity	24	Experimental, Food and Agricultural Organization 2013
Maximum Reproductive Salinity	35	Experimental, Food and Agricultural Organization 2013
Minimum Duration	12	At 27-30 C, (Toba et al. 1992, cited by Inoue et al. 2012)
Maximum Duration	24	At 18 C, (Toba et al. 1992, cited by Inoue et al. 2012)
Minimum Length (mm)	15	Minimum size at spawning (Ponurovsky and Yakolev 1992)
Maximum Length (mm)	79	Gillespie et al. 2012, but a more usual maximum is ~50 mm (Abbott 1974).
Broad Temperature Range	None	Cold temperature-Tropical
Broad Salinity Range	None	Mesohaline-Euhaline

General Impacts

Venerupis philippinarum is one of the most widely cultivated clam species in the world, both in its native Asian range, and in its introduced range in North America and Europe. It is a popular seafood species, and can be reared in dense populations in shallow waters (Breber 2002; Gillespie et al. 2102; Food and Agricultural Organization 2013). As a major new filter-feeder in its invaded regions, it has had important impacts on benthic communities, some resulting from the clams themselves, but larger impacts may have resulted from human disturbance due to harvesting and aquaculture (Breber 2002; Streftaris and Zenetos 2006; Ruesink et al. 2006; Pranovi et al. 2008; Bendell et al. 2010; Queiros et al. 2011; Sladonja et al. 2011).

Economic Impacts

Fisheries - Venerupis philippinarum is now one of the most widely harvested and consumed clams in the world. In 2010, worldwide production was 3.6 million metric tons. The 2nd highest production in the world in 2002 was in Italy with 41,000 metric tons, while the United States and France produced more than 1,000 tonnes each (Food and Agricultural Organization 2013). In 2004, Canada (British Columbia) harvested 1,500 tonnes (Whiteley and Bendell-Young 2007). Japanese Littlenecks are easily harvested, because they are shallow burrowers (California Department of Fish and Game 2001). In the US, they are frequently steamed, and eaten on the hard-shell. They are highly regarded for their flavor, according to cooking websites.

'Manila Clams' or 'Japanese Littlenecks' are often farmed by planting hatchery-raised seed, about 10-15 mm in size. They are planted in intertidal beach areas, or in shallow oyster ponds, at high density (Breber 2002; Carswell et al. 2006; Whiteley and Bendell-Young 2007; Sladonja et al. 2011; Food and Agriculture Organization 2013). The planted areas in British Columbia are often covered with plastic netting to prevent predation (Carswell et al. 2006; Munroe and McKinley 2007). In addition to aquaculture and commercial harvesting of 'wild' clams, recreational harvesting of these clams is popular in Europe and on the West Coast of the US (California Department of Fish and Game 2001; Fisheries and Oceans Canada 2009; Sladonja et al. 2011; Washington Department of Fish and Wildlife 2013). Both commercial and recreational fisheries are subject to closures because of industrial and agricultural pollution, and because of the occurrence of toxic algal blooms (California Department of Fish and Game 2001; Fisheries and Oceans Canada 2009; Sladonja et al. 2011; Washington Department of Fish and Wildlife 2013).

Ecological Impacts

Competition - The extent to which V. philippinarum displaces native bivalves by competition for food or space is unclear. On British Columbia intertidal shores, the density of other bivalves was not affected in beds of farmed Manila Clams, compared with reference sites (Whiteley and Bendell-Young 2007). However, a later survey in British Columbia indicates that V. philippinarum is replacing the native Pacific Littleneck (Leukona staminea) in farmed and non-farmed areas, despite the introduced clam's greater vulnerability to predation (Bendell 2014). In lagoons of the northern Adriatic, where V. philippinarum is intensively farmed, the native V. decussata (Grooved Carpet Shell) has become rare, but is still present. However, the sites where V. philippinarum is now most abundant, had relatively low densities of native species (Breber 2002).

Hybridization - A few hybrids between V. philippinarum and the native V. decussata (9 of 222 putative V. decussata - 4%) have been found in the Ria de Vigo, Spain. However, the extent and significance of genetic exchange between the two species is not known (Hurtado et al. 2011).

Habitat Change - As a relatively large and active, but shallow burrower, V. philippinarum is an important contributor to bioturbation in estuaries, but the importance of this effect in different areas (Poole Harbour, Bay of Arcachon, and Venice Lagoon) depended on sediment qualities, the presence of vegetation, and the other bioturbators in the community (Queiros et al. 2011). However, the largest effect of this species on habitats is due to the human development of aquaculture, which includes intensive planting of seed clams, increased deposition of organic matter, use of nets to exclude predators, and disturbance of sediments during commercial and recreational harvesting (Breber 2002; Carswell et al. 2006; Munroe and McKinley 2007; Bendell et al. 2010; Sladonja et al. 2011; Gillespie et al. 2012).

Food/Prey - As a large bivalve which frequently develops very high densities and biomasses, V. philippinarum is a potentially important prey item for a wide variety of predators in shallow subtidal and intertidal waters (Cohen et al. 2005; Gillespie et al. 2012). Its comparatively short siphon means that it is a relatively shallow burrower, and so more vulnerable. Buried clams with their extended siphons are often subject to sublethal predation, where the siphon is cropped by crabs and fishes. The siphon regrows, but V. philippinarum is forced to feed closer to the surface, making it more vulnerable to lethal predators, while the Pacific Littleneck (Leukoma staminea) with a longer siphon can remain at a safer depth (Meyer and Byers 2005). Major underwater predators include moon snails, crabs (Cancer productus, Metacarcinus magister, Carcinus maenas), starfish and a variety of fishes (Palacios and Ferraro 2003; Cohen 2005; Dudas et al. 2006; Cloern et al. 2007; Gillespie et al. 2012). Air-breathing predators include sea ducks, such as Scoters (Melanitta sp.); shorebirds, such as Oystercatchers (Haematopus spp.); otters; and raccoons (Cohen 2005; Caldow et al. 2007; Gillespie et al. 2012). In the case of the Eurasian Oystercatcher, the presence of populations of V. philippinarum appears to decrease winter mortality (Caldow et al. 2007).

Parasite/Predator Vector - In Atlantic and Mediterranean Spain, V. philippinarum and the native V. decussata suffered mortality due to protozoan parasites of the genus Perkinsus (Sagrista et al. 1996; Cigarria et al. 1997). The parasites appear to be native to the Northwest Pacific, and introduced to European waters with V. philippinarum. At least two species P. olseni and P. honshuesis are known from Asian V. philippinarum. The presence of these parasites has resulted in restrictions of importations to or transfers within European waters (Elston et al. 2003; Dungan and Reece 2006).

Trophic Cascade - Pranovi et al. (2008) argued that filter-feeding by V. philippinarum and other opportunistic species, and the disturbance due to clam harvesting, have altered the Lagoon of Venice's food web (Pranovi et al. 2008), reducing phytoplankton biomass and shifting the food web to one dominated by benthic filter-feeders (Pranovi et al. 2008). The extent to which this occurs in other systems is difficult to assess. The impacts of V. philippinarum may be limited by it short siphon, and tendency to filter benthic microalgae in the bottom surface films (Breber 2002).

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Regional Impacts

MED-VII	None		Ecological Impact	Competition
Ruditapes philippinarum is now the dominant filter-feeder in the lagoons of the northern Adriatic (Pranovi et al. 2008). The native Venerupis decussata has become rare, but has not been eliminated. The native clam is now sold separately, at a higher price, due to 'snob appeal' (Breber 2002).
MED-VII	None		Ecological Impact	Herbivory
Ruidtapes philippinarum is now the dominant filter-feeder in the Lagoon of Venice (Breber 2002; Pranovi et al. 2008).
MED-VII	None		Ecological Impact	Trophic Cascade
Filter-feeding by Ruditapes philippinarum and other opportunistic species now dominates the Lagoon of Venice's food web (Pranovi et al. 2008), reducing phytoplankton biomass, and shifting the food web to one dominated by benthic filter-feeders (Pranovi et al. 2008).
MED-VII	None		Economic Impact	Fisheries
Aquaculture and harvesting of 'wild' Ruditapes philippinarum is now the primary fishery of the lagoons of the northern Adriatic, and the source of 95% of Italian clam production and 90% of the European R. philippinarum harvest (Sladonja et al. 2011). Mechanical harvesting of clams is now the dominant fishery in the Lagoon of Venice (Pranovi et al. 2008). Vibrating rakes have resulted in disturbance and resuspension of sediments, and have adversely affected habitats and other fisheries in the lagoon of Venice. A return to manual harvesting is desirable, but not economically feasible, unless encouraged by government incentives (Nunes and Markandya 2008).
NEA-II	None		Ecological Impact	Habitat Change
In Poole Harbour, England, R. philippinarum, was the second most important species contributing to bioturbation of sediments (Queiros et al. 2011).
NEA-V	None		Ecological Impact	Habitat Change
In the Basin of Arcachon, France, R. philippinarum, was the third most important species contributing to bioturbation of sediments (Queiros et al. 2011).
MED-VII	None		Ecological Impact	Habitat Change
In the Lagoon of Venice, Italy, R. philippinarum, was the second most important species contributing to bioturbation of sediments (Queiros et al. 2011). However, a much larger factor in bioturbation is probably the effects of mechanical harvesting of the clams with vibrating rakes, which has led to extensive resuspension of sediments and siltation, with negative effects on habitat quality (Pranovi et al. 2008, Nunes and Markandya 2008).
NEP-III	Alaskan panhandle to N. of Puget Sound		Economic Impact	Fisheries
Ruditapes philippinarum is intensively farmed on the southern coast of British Columbia. These farms are planted with a high density of clam seed in leased sections of beaches, and often covered by netting to restrict predators (Carswell et al. 2006; Munroe et al. 2007; Whiteley and Bendell-Young 2007; Bendell et al. 2010). In Baynes Sound, these farms occupied about 20% of the shoreline, with 3% covered by netting (Carswell et al. 2006). Japanese littlenecks are also frequently harvested by recreational shellfishers in British Columbia and Washington (Fisheries and Oceans Canada 2009; Washington Department of Fish and Wildlife 2013)
NEP-III	Alaskan panhandle to N. of Puget Sound		Ecological Impact	Habitat Change
Sites in which farming of R. philippinarum took place had 'significantly greater amounts of ammonium, phosphorus and manganese in bulk and organic matter, and ammonium, iron, manganese and silt in surficial sediments' (Bendell et al. 2010). Antipredator nets at these sites may increase the deposition of silt and sediments (Bendell et al. 2010). However, farming activity did not affect the abundance of other bivalve species at the sites (Whiteley and Bendell-Young 2007).
NEA-V	None		Ecological Impact	Hybridization
Of 328 'Venerupis' spp. sampled in the Ria de Vigo, Spain, nine were apparent hybrids, based on DNA sequences and chromosome studies. The spawning seasons of these two bivalves partially overlap and the chromosomes of hybrids appear to pair normally (Hurtado et al. 2011). However, the frequency and significance of genetic exchange between the species is not known.
NEP-III	Alaskan panhandle to N. of Puget Sound		Ecological Impact	Food/Prey
Ruditapes philippinarum may be more vulnerable to predators than the native Leukoma staminea (Pacific Littleneck) because of its shorter siphon. Simulated sublethal predation (cropping the siphon) caused R. philippinarum to bury at shallower Repths, making it more vulnerable to predators, while L. staminea, even after losing 40% of its siphon, remained at the same depth (Meyer and Byers 2005). Sea ducks (Surf Scoter- Melanitta perspicillata; White-Winged Scoter- M. fusca) fed primarily on R. philippinarum and Nuttallia obscurata (Purple Varnish Clam) in Britsh Columbia waters. Scoter predation appeared to be the primary cause for winter decline in these bivalves (Lewis et al. 2007).
SP-XXI	None		Economic Impact	Fisheries
Ruditapes philippinarum was stocked, several times in Oahu, possibly in the 1880-90s, and then before 1918, and in 1920, and then transplanted to other islands. Harvesting at several locations has been intense enough to reduce, or eliminate local populations (Yap 1977; Carlton and Eldredge 2009).
NEP-IV	Puget Sound to Northern California		Ecological Impact	Food/Prey
Palacios and Ferraro (2003) found that Carcinus maenas (Green Crabs) fed at high rates on R. philippinarum and other bivalves at high rates, though O. lurida (Olympic Oysters) were the preferred prey.
P290	Puget Sound		Economic Impact	Fisheries
Ruditapes philippinarum (Manila Clam, Japanese Littleneck) is reared in shellfish farms and fished recreationally in Puget Sound (Washington Department of Fish and Wildlife 2013).
P280	Grays Harbor		Economic Impact	Fisheries
Japanese littlenecks are frequently harvested by recreational shellfishers in Washington. Copalis Beach, in Grays Harbor, is a popular site (Washington Department of Fish and Wildlife 2013).
P270	Willapa Bay		Economic Impact	Fisheries
Ruditapes philippinarum (Manila Clam, Japanese Littleneck) is reared in shellfish farms and fished recreationally in Willapa Bay (Ruesink et al. 2006; Washington Department of Fish and Wildlife 2013).
NEP-IV	Puget Sound to Northern California		Economic Impact	Fisheries
Ruidtapes philippinarum (Manila Clam, Japanese Littleneck) is reared in shellfish farms in Willapa Bay and Humboldt Bay, and fished recreationally in Grays Harbor, Willapa Bay and Humboldt Bays (Ruesink et al. 2006; California Department of Health Services 2007; Washington Department of Fish and Wildlife 2013, http://wdfw.wa.gov/fishing/shellfish/clams/).
P130	Humboldt Bay		Economic Impact	Fisheries
Ruditapes philippinarum (Manila Clam, Japanese Littleneck) is reared in shellfish farms in Humboldt Bay in small quantities (California Department of Health Services 2007).  Recreational shellfishing for these clams is also popular (California Department of Fish and Game 2001).
NEP-V	Northern California to Mid Channel Islands		Economic Impact	Fisheries
San Francisco Bay supports dense populations of Ruditapes philippinarum, which have attracted recreational clammers. However, water quality issues have limited harvests (California Department of Fish and Game 2001). In Tomales Bay, they are cultured as 'Manila Clams' in several shellfish farms, according to local websites.
NEP-V	Northern California to Mid Channel Islands		Ecological Impact	Food/Prey
Ruditapes philippinarum is a common food item for moon snails, sturgeon, gulls, shorebirds, ducks, and raccoons (Cohen and Carlton 1995).
P110	Tomales Bay		Economic Impact	Fisheries
In Tomales Bay, Ruditapes philippinarum are cultured as 'Manila Clams' in several shellfish farms, according to local websites.
P090	San Francisco Bay		Economic Impact	Fisheries
San Francisco Bay supports dense populations of Ruditapes philippinarum, which have attracted recreational clammers. However, water quality issues have limited harvests (California Department of Fish and Game 2001).
P050	San Pedro Bay		Ecological Impact	Competition
In Colorado Lagoon, Long Beach CA, Ruditapes philippinarum became the biomass dominant in the benthic community by 2004, as the previous dominant, the introduced Hard Clam, Mercenaria mercenaria, disappeared. Competition is possible, but when R. philippinarum appeared, M. mercenaria had already become rare (Burnaford et al. 2011).
NEP-VI	Pt. Conception to Southern Baja California		Ecological Impact	Competition
In Colorado Lagoon, Long Beach, CA Ruditapes philippinarum became the biomass dominant in the benthic community by 2004, as the previous dominant, the introduced Hard Clam, Mercenaria mercenaria, disappeared. Competition is possible, but when R. philippinarum appeared, M. mercenaria had already become rare (Burnaford et al. 2011).
NEA-III	None		Economic Impact	Fisheries
Although Ruditapes philippinarum does not breed in Irish waters, Ireland supports successful hatchery-based culture operations in Drumcliff Bay, Cork Harbour, and other locations (Drummond et al. 2006).
NEA-II	None		Economic Impact	Fisheries
In French waters, hatchery stocks were established in 1972, and a commercial fishery was established by 1984. By 1992, it was sustained by natural breeding, although adversely affected by Vibrio infections. The harvested clams were mostly exported to Spain (Flaasch and LeBorgne 1992). A winter fishery has developed in Poole Harbour, England, for R. philippinarum. The fishery depresses clam abundance, but appears to be sustainable (Humphreys et al. 2007).
NEA-IV	None		Economic Impact	Fisheries
In French waters, hatchery stocks were established in 1972, and a commercial fishery was established by 1984. By 1992, it was sustained by natural breeding, although adversely affected by Vibrio infections. The harvested clams were mostly exported to Spain (Flaasch and LeBorgne 1992).
NEA-V	None		Economic Impact	Fisheries
In French waters, hatchery stocks of R. philippinarum were established in 1972, and a commercial fishery was established by 1984. By 1992, it was sustained by natural breeding, although adversely affected by Vibrio infections. The harvested clams were mostly exported to Spain (Flaasch and LeBorgne 1992). In Spain, culture of this clam began in 1980 (Cigarria et al. 1997). A fishery for R. philippinarum in the Ria Arousa, Spain, has been proposed to be certified as environmentally sustainable by the Marine Stewardship Council, Spain, a designation which is disputed by Galil et al. (2013).
NEA-II	None		Ecological Impact	Food/Prey
In Poole Harbour, England, R. philippinarum may be an important food for Eurasian Oystercatchers (Haematopus ostralegus), a bird considered to be an indicator of ecosystem health (Jensen et al. 2004). Modeling suggests that the high density of R. philippinarum has reduced winter mortality of the Eurasian Oystercatcher at Poole Harbour. The spread of this clam is considered a potential benefit to European shorebirds (Caldow et al. 2007). Excretion of inorganic carbon and nutrients by R. philippinarum stimulates microbial activity in intertidal sandflats, both when submerged at high tides, and energed at low tides (Mign et al. 2018). However, it is unclear whether these effects are different feom those of natïve bivalves.
NEA-V	None		Ecological Impact	Parasite/Predator Vector
In the Eo estuary, Spain, R. philippinarum has suffered mortality due to protozoan parasites of the genus Perkinsus (Cigarria et al. 1997). The parasites appear to be native to the Northwest Pacific, and introduced to European waters. At least two species, P. olseni and P. honshuesis, are known from Asian R. philippinarum (Elston et al. 2003; Dungan and Reece 2006).
MED-II	None		Ecological Impact	Parasite/Predator Vector
Perkinsus olseni (as P. atlanticus) was reported to cause serious mortality of R. philippinarum and Venerupis decussata on clam farms in the Ebro Delta, Spain.
NEP-III	Alaskan panhandle to N. of Puget Sound		Ecological Impact	Competition
Ruditapes philippinarum appears to be replacing the native Leukoma staminea (Pacific Littleneck) in farmed areas and reference sites, despite its greater vulnerablity to predators, partly because of the intensity of seeding in farmed areas (Bendell 2014).
NEA-V	None		Ecological Impact	Competition
Ruditapes philippinarum is considered a potential competitor of the native Venerupis decussatus, but the two species differ somewhat in their ecological preferences, with R. philippinarum being more abundant in regions of less sand, slower current, ande higher organic content (Bidegain et al. 2015). In the Tagus estuary, Portugal, the growth performance of R. philippinarum was much higher than that of V. decussatus, whise population is delining (Moura et al. 2017).
NEA-V	None		Ecological Impact	Herbivory
Brito et al. (2015) have attributed a decrease in phytoplankton abundance and average size, in the Tagus estuary, Portugal, to development of a large biomass of R. philippinarum. They estimate that R. philippinarum could clear the water column in 10 days (Brito et al. 2015).
HI	Hawaii		Economic Impact	Fisheries
Ruditapes philippinarum was stocked, several times in Oahu, possibly in the 1880-90s, and then before 1918, and in 1920, and then transplanted to other islands. Harvesting at several locations has been intense enough to reduce, or eliminate local populations (Yap 1977; Carlton and Eldredge 2009).
WA	Washington		Economic Impact	Fisheries
Ruditapes philippinarum (Manila Clam, Japanese Littleneck) is reared in shellfish farms and fished recreationally in Willapa Bay (Ruesink et al. 2006; Washington Department of Fish and Wildlife 2013)., Japanese littlenecks are frequently harvested by recreational shellfishers in Washington. Copalis Beach, in Grays Harbor, is a popular site (Washington Department of Fish and Wildlife 2013)., Ruditapes philippinarum (Manila Clam, Japanese Littleneck) is reared in shellfish farms and fished recreationally in Puget Sound (Washington Department of Fish and Wildlife 2013).
CA	California		Ecological Impact	Competition
In Colorado Lagoon, Long Beach CA, Ruditapes philippinarum became the biomass dominant in the benthic community by 2004, as the previous dominant, the introduced Hard Clam, Mercenaria mercenaria, disappeared. Competition is possible, but when R. philippinarum appeared, M. mercenaria had already become rare (Burnaford et al. 2011).
CA	California		Ecological Impact	Food/Prey
Ruditapes philippinarum is a common food item for moon snails, sturgeon, gulls, shorebirds, ducks, and raccoons (Cohen and Carlton 1995).
CA	California		Economic Impact	Fisheries
San Francisco Bay supports dense populations of Ruditapes philippinarum, which have attracted recreational clammers. However, water quality issues have limited harvests (California Department of Fish and Game 2001). In Tomales Bay, they are cultured as 'Manila Clams' in several shellfish farms, according to local websites., Ruditapes philippinarum (Manila Clam, Japanese Littleneck) is reared in shellfish farms in Humboldt Bay in small quantities (California Department of Health Services 2007).  Recreational shellfishing for these clams is also popular (California Department of Fish and Game 2001)., San Francisco Bay supports dense populations of Ruditapes philippinarum, which have attracted recreational clammers. However, water quality issues have limited harvests (California Department of Fish and Game 2001)., In Tomales Bay, Ruditapes philippinarum are cultured as 'Manila Clams' in several shellfish farms, according to local websites.

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