Invasion History

First Non-native North American Tidal Record: 1902
First Non-native West Coast Tidal Record: 1902
First Non-native East/Gulf Coast Tidal Record:

General Invasion History:

Magallana angulata gigas is native to the northwest Pacific including Russia, China, and Korea. Its native range may extend south and west into the Philippines and Indonesia, to Borneo and Sumatra, and west to Pakistan (Carriker and Gaffney 1996). However, the presence of several closely related species and the morphological variation of M. gigas make the boundaries of its range difficult to assess. It is the most widely transplanted shellfish in the world, introduced to at least 52 countries (Food and Agricultural Organization 1998; Ruesink et al. 2005). It is now the world's most widely cultivated oyster. It has established breeding populations in the northeast Pacific (US-Canada), southwest Pacific (Australia-New Zealand), northeast Atlantic-Mediterranean (Europe), southwest Atlantic (Argentina-Brazil), and Indian Ocean (South Africa). It is also successfully cultured using hatcheries and imported spat in many places where conditions are unsuitable for breeding, and has been introduced unsuccessfully to many regions (Food and Agricultural Organization 1998; Ruesink et al. 2005). A repeated pattern in different regions has been for M. gigas to go from being largely confined to culture areas, with only sporadic and limited reproduction, to becoming a major biomass component and ecosystem engineer. This process, which has taken 3-10 decades, has occurred in British Columbia and Washington State (Quayle 1969; Klinger et al. 2006; Kelly et al. 2008; Padilla 2010), the North Sea in Europe (Diederich 2005; Beukema and Dekker 2011), the Atlantic coast of Patagonia (Escapa 2004), Hawaii (Carlton and Eldredge 2009), and Australia (Krassoi et al. 2008). The transition from cultured hatchery-dependent populations, to feral self-sustaining populations complicates the assignment of dates of invasion.

North American Invasion History:

Invasion History on the West Coast:

In North America, Magallana gigas was first introduced to Puget Sound, Washington (WA) in 1902, following overfishing of the native Olympic Oyster (Ostrea lurida) and unsuccessful stocking of M. virginica (Eastern Oyster). Early transplants were unsuccessful due to mortality in shipping, but after numerous subsequent imports, large-scale cultivation was underway in Washington State by 1928 (Chew 1979). In British Columbia, imports began in 1912, but large-scale natural spawning was not seen until 1932 (Quayle 1969). Fairly regular settlement of M. gigas spat, outside areas of cultivation, now occurs from Pendrell Sound, British Columbia, to Willapa Bay, WA (Quayle 1969; Ruesink et al. 2005). This species is now the basis of the West Coast oyster industry, with commercial culture taking place from southern British Columbia to Morro Bay, California (CA) (Chew 1979; Quayle 1969; Conte 1996). However, these operations were largely dependent on imported seed from Japan, and later (1970s onward) on hatchery-reared spat (Barrett 1963; Quayle 1969; Carlton 1979; Conte 1996). South of Willapa Bay, natural spawnings of M. gigas were rare (Span 1978; Carlton 1979; Boyd et al. 2000; Coan et al. 2000), but hatchery-based oyster aquaculture operations occur in several Oregon bays and south to Morro Bay, CA (Carlton 1979; Conte 1996), the Pacific Coast of Baja California (Rodriguez and Ibarra-Obando 2008), and the Gulf of California (Arizpe 1996).

In California, since 2000, there have been collections of 'wild' M. gigas in San Francisco Bay and southern California estuaries (Andy Chang, personal communication; Ruiz et al. unpublished data; Cohen et al. 2002; de Rivera et al. 2005; Burnaford et al. 2011; Goodwin et al. 2011). At least some of the San Francisco Bay occurrences have resulted from the breeding of illegally planted M. gigas (Andy Chang, personal communication). Transport of oysters in ship fouling or larvae in ballast water are also possible vectors. There is some evidence for multiple cohorts of oysters in San Francisco Bay, but at this time we consider the establishment of M. gigas to be uncertain.

Invasion History on the East Coast:

Magallana gigas attracted some attention in the mid-20th century because of its large size and rapid growth. A bushel of Pacific Oysters was planted in Barnegat Bay, New Jersey, but failed to grow, and died within two years. A number of illegal and government plantings were made in estuaries from Delaware to Maine from the 1930s to the 1980s, but settlement of larvae and establishment of Pacific Oysters was not observed (Dean 1979; Hickey 1979; Andrews 1980). There was particular interest in Maine, because of the limited existing Eastern Oyster (M. virginica) stocks there. Plantings were made in 1949 in Blue Hill Bay and in the 1970s in Damariscotta River and Goose Pond, a lagoon of Penobscot Bay (Dean 1979; Shatkin et al. 1997). However, we are not aware of more recent introduction attempts.

Around Chesapeake Bay, interest in M. gigas intensified as the native M. virginica  declined due to overfishing and disease (MSX- Haplosporidium nelsoni, Dermo- Perkinsus marinus). Magallana gigas was considered to be more disease-resistant than the Eastern Oyster, and was considered as a potential replacement, especially in Virginia, where oyster losses were greatest (Andrews 1980; DuPaul 1992). Numerous culture experiments were undertaken with diploid and triploid (sterile) M. gigas in order to assess the disease resistance of the Pacific Oyster and its adaptability to the Chesapeake Bay environment. Experiments in quarantined flumes indicated that M. gigas had lower prevalence and intensity of P. marinus and H. nelsoni infections (Barber 1996; Barber and Mann 1994; Chu et al. 1996; Krantz 1992). Plantings of sterile triploid M. gigas in Chesapeake Bay, Virginia, and North Carolina indicated that this oyster grew well at high salinities, but performed poorly at low salinities (Calvo et al. 1999; Grabowski et al. 2004). Benefits of a disease-resistant oyster would include restoration of the oyster-reef environment and of a filter-feeding biomass in at least part of Chesapeake Bay, as well as revival of oystering (Gottlieb and Schweighofer 1996; Lipton et al. 1992; Mann et al. 1991). Although M. gigas showed strong disease resistance, trials in Chesapeake Bay suggested that this oyster was not well-adapted to the local environment. In quarantined flumes, M. gigas had high non-disease mortality in summer (Barber and Mann 1994), and heavy Polydora spp. infestations (Mann and Burreson 1994; DeBrosse and Allen 1996). By 1998-2000, research interests in Virginia and North Carolina had shifted to M. ariakensis, which demonstrated better growth and survival under Chesapeake Bay conditions (Hallerman et al. 2001; National Research Council 2003).

Invasion History on the Gulf Coast:

At least one unsuccessful attempt was made to introduce M. gigas to the Gulf Coast. Kavanaugh (1941) reported very briefly that 'Japanese oysters' in Louisiana, showed 'amazingly serious infestation' by spionid polychaetes (Polydora spp.), and that native oysters were not seriously affected. This is the only report that we have of this oyster in the Gulf of Mexico.

Invasion History in Hawaii:

A small shipment of M. gigas was planted at Mokapu, Oahu on Kaneohe Bay in 1926, but did not become established. Larger plantings were made at Pearl Harbor in 1938, and in Kaneohe Bay (2 million spat planted) in 1939. Pacific Oysters are now established in Pearl Harbor and abundant in Kaneohe Bay (Coles et al. 1999; Coles et al. 2002; Carlton and Eldredge 2009 - 2000 oysters planted, established).

Invasion History Elsewhere in the World:

In the northeastern Atlantic, Magallana gigas was imported to Marennes, France in small quantities in 1966. This was followed by a disease epizootic in M. angulata (Portuguese Oyster), which was then the predominant commercial species (itself imported to supplant the overfished Ostrea edulis or the European Flat Oyster). Consequently, large imports of M. gigas were made to replace the lost M. angulata stocks (Grizel and Héral 1991). In the United Kingdom, laboratory stocks were imported in 1965 and 1972, and the experimental field plantings of lab-reared spat, in 1967 and 1973. Spawning and recruitment were rare in British waters, owing to low water temperatures (Walne and Helm 1979). Extensive plantings of M. gigas were made in the Atlantic waters of Europe in the 1970s, from Spain to Ireland, and east to Germany and Denmark (Ruesink et al. 2005; Minchin 2007; Troost 2010; Wrange et al. 2010). This culture was largely hatchery-based, but natural spawning and settlement were seen in the 1970s and 1980s in many locations, particularly the Wadden Sea area of the Netherlands, Germany and Denmark (Reise 1998; Gittenberger et al. 2010; Troost 2010; Wrange et al. 2010), where extensive oyster beds were replacing mussel beds by the year 2000. The occurrence of successful spawning and massive recruitment in northern Europe in recent decades has been attributed in part to climate change (Troost 2010; Wrange et al. 2010; Thomas et al. 2016). Successful spawning and apparent establishment took place by 2007 in Espevik, Norway (60⁰N). Established populations also occur in Denmark and Sweden, along the Kattegatt, at the mouth of the Baltic (Wrange et al. 2010) and along the Atlantic coast of France, Portugal and Spain (Grizel and Héral 1991, Ruesink et al. 2005). Hatchery and wild M. gigas populations along the Atlantic coasts of Europe, from Germany (Sylt) to southern France (Arcachon), show little genetic differentiation, being strongly determined by hatchery and aquaculture practices (Meistertzheim et al. 2013).

Magallana gigas, imported from Japan, was first introduced to the Mediterranean Sea by 1964, in the Thau Lagoon, near Sete, France, again as a replacement for declining stocks of Ostrea edulis and M. angulata. It soon was widely cultured in the Mediterranean from Morocco to Israel (Ruesink et al. 2005). This oyster appears to be, at least locally, established in coastal lagoons and estuaries in Tunisia, France, Italy, Greece, and Turkey (Zenetos et al. 2003; Ruesink et al. 2005; Zenetos et al. 2005; Albayrak 2011; Antit et al. 2011). The status of M. gigas in the Black Sea is uncertain - it is known mostly as single individuals near ports and oyster farms (Skarlato and Sarobogov 1972, cited by Zoloterev 1996; Gomiou et al. 2002; Skolka and Preda 2010).

Magallana gigas has been widely cultured in the Southern Hemisphere, beginning in 1947 in Tasmania, Australia (Nell 2001), in 1950 in South Africa (Robinson et al. 2005), and in 1977 in Chile (Castilla et al. 2005). In Chile, Pacific Oysters remain confined to aquaculture facilities, possibly because of low water temperatures (Castilla et al. 2005). However, breeding populations quickly developed in Tasmania and by the 1960s in mainland Australia (Nell 2001), and locally by 2001 on the southern coast of South Africa (Robinson et al. 2005). In Argentina, a failed aquaculture operation led to established populations on the Patagonian coast (Orensanz et al. 2002; Escapa 2004). Surprisingly, spat and adults of M. gigas were identified by molecular means in cultures of native oysters (M. brasiliana and M. rhizophorae) in Brazil, at latitudes between 27 and 29⁰S (Melo et al. 2010). Some populations of M. gigas in New Zealand (1st record 1961, Cranfield et al. 1998) are believed to have resulted in transport by shipping, and are not associated with known aquaculture operations (Krassoi et al. 2008). Pacific Oysters have been widely introduced to tropical and subtropical regions and islands (e.g., Puerto Rico, Virgin Islands, Madeira, Guam, Tonga, Fiji, Belize, Malaysia), but with the exception of Hawaii, these introductions have not resulted in established populations or successful hatchery-based aquaculture (Ruesink et al. 2005). Carrasco and Baron (2010) concluded that M. gigas could establish populations in regions with mean sea surface temperature ranging from 14 to 28.9⁰C for the warmest month and from -1.9 to 19.8⁰C for the coldest month of the year. The Pacific Oyster's occurrence in slightly warmer water in Brazil may have been due to unintentional selection of oysters in Brazilian shellfish laboratories (Melo et al. 2010).


Description

Magallana gigas resembles other oysters in having unequal valves and an irregular shape. The shape of the shell varies greatly with the growth environment. For instance, on hard substrate the shell can be rounded, domed and fluted; on soft substrate it can be flatter and less ridged; and when crowded the shell is often narrower (Quayle 1969). The right (lower) valve may be deeply cupped. Both valves are covered with concentric growth layers (lamellae) on the outer surface, but with fewer and stronger ridges on the left (upper) side. The edges of the lamellae are strongly rippled into spines and ridges (Coan and Valentich-Scott 2007; Langdon and Robinson 1996). Shells can be white to off-white to gray, sometimes with brown or purple on the ridges. The interior of the shell is smooth and white, with a purple muscle scar (Quayle 1969; Coan et al. 2000). Magallana gigas matures at about 80 mm, but is reported to occasionally grow to 400-450 mm (Carriker and Gaffney 1996). The larvae are illustrated by Quayle (1969). Early veligers are nearly circular, but late larvae of this and other oysters are distinguished by the asymmetrical umbo. They settle at a length of about 300 µm (Quayle 1969).

Magallana gigas is a genetically diverse species. In different parts of Japan, different strains are cultivated with different growth patterns and ecological preferences. The most widely planted form is the Miyagi strain, from the central Pacific coast of Japan which is large and fast-growing (Quayle 1969). In addition, many closely related species are found in the Northwest and Indo-West Pacific regions. Magallana angulata (Portuguese Oyster), introduced to Europe in the 16th century, is very closely related (Ó'Foighil et al. 1998; Huvet et al. 2004; Lapegue et al. 2004; Reece et al. 2008).

The genus name Magallana has been proposed for Pacific members of the genus Crassostrea, based on genetic divergence between Pacific and Atlantic oysters of the genus (Salvi et al. 2014; Salvi and Mariottini 2020). Bayne and 23 co-authors disagreed with the proposed name changes, based on the limited scope of the genetic analysis, the absence of morphological differentiation, and the inconveninece of changing thename of an economically important species (Bayne et al. 2017). A further genetic analysis by Salvi and Mariottini (2020) owed that the Indo-Pacific and western Atlantic 'Crassotrea' clustered in two separate groups, justifying the use of the name Magallana for the Indo-Pacific species (James T. Carlton, personal communication).


Taxonomy

Taxonomic Tree

Kingdom:   Animalia
Phylum:   Mollusca
Class:   Bivalvia
Subclass:   Pteriomorphia
Order:   Ostreoida
Family:   Ostreidae
Species:   gigas

Synonyms

Crassostrea angulata (Lamarck, 1819)
Ostrea gigas (Thunberg, 1793)
Magallana gigas (Salvi & Marriotini, 2016)

Potentially Misidentified Species

Alectryonella plicatula
Plicate Kitten's Paw Oyster, Large Indo-Paciifc oyster, cultivated in China (Carriker and Gaffney 1996)

Crassostrea virginica
Eastern Oyster

Magallana angulata
Portuguese Oyster, closely related, native to the northwest Pacific (Japan and China), introduced to Europe in the 16th-17th centuries, and described from the Tagus River, Portugal in 1817 (Wolff and Reise 2002). Genetic barcoding indicates that the two species have been separate for 2.7 million years. Crassostrea anuglata is dominant cupped oyster species in Taiwan and southern China (Hsiao et al. 2016).

Magallana ariakensis
Suminoe Oyster, Chinese River Oyster, native to China, cultured, with unsuccessful introductions in Yaquina Bay, Oregon, and Puget Sound (Carriker and Gaffney 1996)

Magallana hongkongensis
Closely related, cutivated in the Pearl River Delta, China.

Magallana sikamea
The Kumamoto Oyster is under limited cultivation in US waters. It does not spawn in Puget Sound, because of low water temperatures, and so is available in summer, when other oysters are out of season (Washington Sea Grant 2002, http://wsg.washington.edu/oysterstew/cool/oystervarieties.html)

Ostrea lurida
Olympic Oyster, northeast Pacific native

Ecology

General:

Magallana gigas like other oysters, is a protandric hermaphrodite, maturing first as a male, and then often becoming female in subsequent seasons. Females release eggs and males release sperm into the water column, where fertilization occurs. The fertilized egg develops first into a ciliated trochophore larva, and then into a shelled veliger larva. The larva feeds on phytoplankton, and grows, eventually developing a foot and becoming a pediveliger, competent for settlement. In laboratory culture, larval settlement occurred at about 11-30 days at 16 to 30⁰C (Quayle 1969; His et al. 1989). Gonads can develop in M. gigas at 80 mm (National Research Council 2003). Adult M. gigas feed on phytoplankton of 6-32 um with ~100% retention efficiency, but are less efficient with smaller organisms (Nielsen et al. 2016). Adult oysters are reported to grow to 450 mm, although 300 mm in length is a more typical maximum (Quayle 1969; Carriker and Gaffney 1996).

Magallana gigas is characteristic of protected coastal waters in China and Japan. This oyster normally grows at salinities of 23-28 PSU, and can tolerate brief exposures to salinities as low as 5-10 PSU (Nell and Holliday 1988; Carriker and Gaffney 1996; Gray and Langdon 2018). It tolerates a very wide temperature range, from -1.8 to 35⁰C, although temperatures over 30⁰C are stressful (Shpigel et al. 1992; Carrasco and Barón 2010). Settlement and survival are best at sites at sites portected from wave exposure (Teschke et al. 2020).

Food:

Phytoplankton

Consumers:

Crabs, Fishes, Starfish, Humans

Trophic Status:

Suspension Feeder

SusFed

Habitats

General HabitatOyster ReefNone
General HabitatCoarse Woody DebrisNone
General HabitatMarinas & DocksNone
General HabitatRockyNone
General HabitatVessel HullNone
General HabitatMangrovesNone
Salinity RangeMesohaline5-18 PSU
Salinity RangePolyhaline18-30 PSU
Salinity RangeEuhaline30-40 PSU
Tidal RangeSubtidalNone
Tidal RangeLow IntertidalNone
Vertical HabitatEpibenthicNone


Tolerances and Life History Parameters

Minimum Temperature (ºC)-1.8Based on geographical range (Carrasco and Baron 2010).
Maximum Temperature (ºC)35Crassostrea gigas (Pacific Oysters) shows signs of metabolic stress at 30 C (Shpigel et al. 1992; Gray and Langdon 2018).
Minimum Salinity (‰)5Substantial growth and reproduction occurs only above 20 ppt. (His et al. 1989; Mann et al. 1991; Nell and Holliday 1988; Gray and Langdon 2018).
Maximum Salinity (‰)41Successful aquaculture, Nell and Holliday 1988
Minimum Reproductive Temperature16Field and experimental data (His 1991; Mann et al. 1991)
Maximum Reproductive Temperature30Field and experimental data (His 1991; Mann et al. 1991)
Minimum Reproductive Salinity15Experimental conditions for larval growth (Nell and Holliday 1988). Optimum salinities for reproduction and larval growth are 20-30 ppt (His et al. 1989; Mann et al. 1991; Nell and Holliday 1988).
Maximum Reproductive Salinity40Experimental conditions for larval growth (Nell and Holliday 1988). Optimum salinities for reproduction and larval growth are 20-30 ppt (His et al. 1989; Mann et al. 1991; Nell and Holliday 1988).
Minimum Duration11Larval Period (His et al. 1989)
Maximum Duration30Larval Period (His et al. 1989)
Minimum Length (mm)80Carriker and Gaffney (1996)
Maximum Length (mm)450Carriker and Gaffney (1996)
Broad Temperature RangeNoneCold temperate-Warm temperate
Broad Salinity RangeNoneMesohaline-Euhaline

General Impacts

Magallana gigas is the world's most widely cultivated and eaten shellfish (Carriker and Gaffney 1996; Ruesink et al. 2005), but it is also a highly successful invader, and a powerful ecosystem engineer, creating complex reefs, replacing native shellfish, and altering estuarine foodwebs through suspension-feeding (Herbert et al. 2016).

Economic Impacts

Fisheries - Magallana gigas is the most widely cultivated and harvested shellfish species in the world, introduced to at least 52 countries (Carriker and Gaffney 1996; Ruesink et al. 2005). Among the more notable introductions have been those to the west coast of North America (Chew 1979; Quayle 1969), European waters (Grizel and Héral 1991; Walne and Helm 1979), and Australia (Nell 2001). The disease resistance of this oyster, its adaptability to a wide range of environments, the long development of culture techniques, and its large size are among the reasons for its widespread introduction (Quayle 1969; Andrews 1980; Mann et al. 1991; Ruesink et al. 2005). Profitable culture in natural waters is possible, using hatcheries or imported seed, even in regions where M. gigas cannot breed successfully in the wild, such as California and Pacific Mexico (Arizpe 1996; Conte 1996; Ruesink et al. 2005).

Disadvantages include bland flavor compared to other species, including Ostrea eduis and M. virginica (DuPaul 1992), and risks to native oyster populations, including competition, hybridization, and introductions of associated organisms (parasites, fouling species and oyster predators) (Galtsoff 1932; Grizel and Héral 1991; Mann et al. 1991; Ruesink et al. 2005). In the Wadden Sea area of northern Europe, settlement of M. gigas has covered valuable beds of mussels (Mytilus edulis) and cockles (Cerastoderma edule), and interfered with the use of fishnets (Troost 2010). In Willapa Bay and Grays Harbor, Washington (WA), the pesticide Carbaryl is used to kill mud shrimps which burrow in oyster beds, creating general environmental concerns, as well as killing other fisheries species, such as Dungeness Crabs (Metacarcinus magister) and English Sole (Parophrys vetulus).

Ecological Impacts

Competition - Introductions of new oyster species are often motivated by the decline of the previously dominant oyster due to overfishing or disease, but in some cases they have led to further damage to the remaining populations. Introductions of M. angulata (Portuguese Oyster) in France coincided with the decline of the native Ostrea edulis (European Flat Oyster) in the 19th century (Galtsoff 1932); the replacement of M. angulata by M. gigas in the 1970's seems to have largely been a consequence of a disease of unknown origin (Grizel and Héral 1991). In Australia, competition with M. gigas is considered a threat to the native Saccostrea commercialis (Sydney Rock Oyster) (Mann et al. 1991; Nell 2001). On the West Coast of North America, competition between M. gigas and the native Olympia Oyster (Ostrea lurida) is limited since M. gigas tends to settle, and is cultivated in intertidal areas, while the native oyster tends to grow in lower intertidal and subtidal areas. However, where they do overlap, M. gigas grows much faster, and has a higher filtration rate (Ruesink et al. 2005).

Magallana gigas also competes for space and food with bivalves other than oysters, such as Mytilus edulis (Blue Mussel) and Cerastoderma edule (Common Cockle). In the Wadden Sea (southern North Sea) of Netherlands-Germany-Denmark, M. gigas has been settling on intertidal mussel and cockle beds (Reise 1998; Diederich 2005).

Habitat Change - Both cultivated populations of M. gigas and naturally settled reefs can make large structural changes in littoral communities. These changes are greatest in soft-bottom habitats, such as Willapa Bay, WA; Bahia Anagada, Argentina; and the Wadden Sea (southern North Sea) of Netherlands-Germany-Denmark, which include vast intertidal mudflats. Cultivation takes place on man-made structures, while natural beds result from settlement on mussel beds, logs, or other isolated hard substrates (Escapa 2004; Ruesink et al. 2005; Ruesink et al. 2006; Troost 2010). Cultivated and natural beds create large, complex structures, with extensive hard substrate for organisms to settle on, and lots of nooks and crannies providing shelter for native and introduced mobile organisms (Escapa 2004; Diederich 2005; Hosack et al. 2006; Ruesink et al. 2006; Gittenberger et al. 2010; Markert et al. 2010; LeJart and Hily 2011). While Pacific Oysters settle on and cover mussel beds, they also provide substrate for mussel settlement, and can result in increased biodiversity in their invaded habitats (Markert et al. 2010; LeJart and Hily 2011). On hard substrates, such as rocky shores, impacts of M. gigas are less dramatic (Ruesink et al. 2005). However, intertidal oysters provide a light-colored substrate, cooler than exposed dark rocks, and favoring the survival of limpets (Lottia sp.) at high tide (Padilla 2010), and also increase habitat for barnacle settlement (Bourne 1979, cited by Ruesink et al. 2005). The deposits of pseudofeces can also increase the diversity and abundance of deposit feeders (LeJart and Hily 2011).

Invasions by M. gigas do have negative impacts on habitats. Their high filtration rates result in the deposition of partially digested pseudofeces, which can accumulate around the oyster beds, creating anoxic zones in the sediment, limiting infauna and adversely affecting eelgrass beds (Kelly et al. 2008; Troost 2010). The large accumulations of shell which M. gigas creates in the intertidal zone have a negative effect on the native oyster (O. lurida) by attracting large numbers of settling larvae to the intertidal zone, where their survival is poor, acting as a recruitment sink (Ruesink et al. 2005).

Parasite-Predator vector - In many regions of the world, parasites, epifauna, and predators have been imported with shipments of M. gigas. Known parasites of M. gigas which are now established on the Pacific coast of North America, or in France, include three viruses, three bacterial diseases, three protistans (other than haplosporidians) (Marteilia refringens, Marteilioides chungmuensis and Mikrocytos mackini), the copepod Mytilicola orientalis, and at least one disease of unknown etiology (Mann et al. 1991). The first imports of M. gigas to France coincided with a viral epizootic which largely wiped out the then-dominant commercial oyster M. angulata (Portuguese Oyster), but the origin of this disease is unknown (Grizel and Héral 1991). Many species of macro-organisms have been introduced to, or transferred locally in European and West Coast waters with M. gigas, these include macroalgae (eg. Sargassum muticum), flatworms (Pseudostylochus ostreophagus), snails (e.g. Pteropurpura inornata, Japanese Oyster Drill), clams, bryozoans (Schizoporella japonica), and tunicates (Perophora japonica, Styela clava). Some of these species have had negative impacts on oysters and surrounding communities (Cohen and Carlton 1995; Grizel and Héral 1991; Mann et al. 1991; Cohen et al. 1998; Reise et al. 1999; Goulletquer et al. 2002).

However, the associate of M. gigas which has had the largest ecological and economic impact is probably the protist Haplosporidium nelsoni, which infects the Pacific Oyster with minimal symptoms, but produces the symptoms of the MSX disease, with high mortality, in the Eastern Oyster (M. virginica) (Friedman 1996; Burreson et al. 2000). From 1958 to the present, outbreaks of this disease have caused high mortality in Chesapeake and Delaware Bays, and elsewhere on the East Coast of North America. It seems likely that one of the many early unofficial introductions of M. gigas to the East Coast may have introduced H. nelsoni, although transport of oysters in fouling or spores in ballast water cannot be excluded (Burreson et al. 2000).

In a sort of reverse-parasite vector role, Magallana gigas, together with the Common Atlantic Slipper Shell Crepidula fornicata and other filter feeders, such as the Softshell Clam (Mya arenaria) were found to affect transmission of native parasites (the trematode Himasthla elongata) of the Common Cockle (Cerastoderma edule) and the Blue Mussel (Mytilus edulis), by filtering out the metacercariae, without becoming infected themselves. The effect of these invaders was to reduce the parasite load of the native bivalves (Thieltges et al. 2008; Thieltges et al. 2009).

While it is a highly desired seafood item, Magallana gigas is also an ecosystem engineer and poses a challenge to managers of marine protected areas. This oyster can interfere with native mussel fisheries, create reefs which can obstruct navigation, litter beaches with 'razor-sharp' shells, and drastically effect native marine communities. Regional planning and risk assessment is desirable for oyster culture operations in new areas. Environmental measurements can be used to determine the risk of reproduction of cultured oysters. One option is to require use of triploid oysters in culture, to limit reproduction, but reversion of triploids can occur. Heavy settlement of 'wild' oysters can interfere with culture operations by fouling equipment and cultured oysters. Dredging has been used to eliminate 'wild' oysters, but the habitat damage is considerable. In some areas, hand collection is sufficient to maintain oyster-free zones (Herbert et al. 2016).

Regional Impacts

NEP-IIIAlaskan panhandle to N. of Puget SoundEcological ImpactHabitat Change
On San Juan Island, Washington, intertidal M. gigas altered rocky shore communities by providing a light-colored substrate, decreasing substrate temperatures from a maximum of 56°C to 41°C. On average, oysters were 3.3°C cooler than surrounding rocks, and supported higher densities of limpets (4 species, Lottia strigatella, L. pelta, L. scutum, and L. digitalis). The most abundant limpet, L. strigatella was 3X more abundant on oysters than on surrounding rocks (Padilla 2010; Herbert et al. 2016). On rocky shores of British Columbia, where M. gigas primarily recruits in the upper intertidal zone, it increases the amount of habitat available for barnacle settlement (Bourne 1979, cited by Ruesink et al. 2005). Expanding cultivated and feral oyster beds of M. gigas have resulted in the reduction of Eelgrass (Zosters marina) beds on Cortes Island, in Georgia Strait, British Columbia. Eelgrass tends to disappear in areas seaward of the beds as well. These areas had reduced abundance of epifaunal invertebrates, but increased abundance of infauna (Kelly et al. 2008). The large accumulations of shells which M. gigas creates in the intertidal zone has a negative effect on the native oyster by attracting large numbers of settling larvae of O. lurida, in the intertdal zone, where their survival is poor, acting as a recruitment sink (Ruesink et al. 2005).
P292_CDA_P292 (San Juan Islands)Ecological ImpactHabitat Change
On San Juan Island, Washington, intertidal M. gigas altered rocky shore communities by providing a light-colored substrate, decreasing substrate temperatures from a maximum of 56°C to 41°C. On average, oysters were 3.3°C cooler than surrounding rocks, and supported higher densities of limpets (4 species, Lottia strigatella, L. pelta, L. scutum, and L. digitalis). The most abundant limpet, L. strigatella was 3X more abundant on oysters than on surrounding rocks (Padilla 2010).
NEA-IINoneEcological ImpactHabitat Change
On the Wadden Sea Coast of Germany and the Netherlands, M. gigas has been settling on mussel (Mytilus edulis) beds growing on mudflats, since at least 1991, resulting in overgrowth of mussels and attached barnacles, converting mussel beds to extensive oyster beds (Reise 1998; Diederich 2005; Gittenberger et al. 2010; Walles et al. 2015; Herbert et al. 2016). Oysterbeds provide potential habitat for attached algae, but native forms are outcompeted by the introduced Sargassum muticum (Lang and Buschbaum 2010). Overall, C. gigas beds supported greater abundance and diversity of native epi-and infauna than mussel beds (Markert et al. 2010). Oyster reefs are stablilizing the sediment, but also increasing the deposition of organic material (as pseudofeces), forming anoxic layers (Troost 2010). In experimental plantings, the polychaete Lanice conchilega was more abundant on oyster rings and the oligochaete Tubificoides benedeni on mussel rings (Kochman et al. 2013). Settling of spat of C. gigas on shells of Littorina littorea (Common Periwinkle) had adverse impacts on the movement, growth, and reproduction of this snail in the Wadden Sea (Germany) (Eschweiler and Buschbaum 2011). While invasion of mudflat and mussel bed habitats altered the density and diversity of epifauna, benthic assemlages were similar between C. gigas and native Ostrea edulis communities in Strangford Lough, Northern Ireland (Zwerschke et al. 2016; Zwerschke et al. 2018). However, a later study in Strangford Lough found that epibiota were more diverse on O. edulis than M. gigas, possibly because of the flakier nature of the M. gigas shell (Guy et al. 2018).

The development and consolidation of Pacific Oyster beds in the Wadden Sea has had mixed effects on shorebirds. Eurasian Oystercatchers (Haematopus ostralegus) fed more easily when oysters successfully recruited, while as young oysters grew, and the reef consolidated, feeding was more difficult, but birds were able to maintain a steady intake. Eurasian Curlews (Numenius arquata) were favored by increased density of Green Crabs (Carcinus maenas), while the feeding of Herring Gulls (Larus argentatus) was hampered by the replacement of mussel beds with oysterbeds (Markert et al. 2013). Waser et al. (2016) found that 46 of 50 species of shore- and waterbirds were not affected by the replacement of mussels with oysters. However, the abundances of 4 birds, Common Gulls (Larus canus), Common Eiders (Somateria mollissima), Eurasian Oystercatchers (Haematopus ostralegus), and Red Knots (Calidris canutus) was reduced when oysters were dominant. On the whole, the authors considered that negative impacts from oyster removal exceeded the oysters' negative impacts on bird populations (Waser et al. 2016). On a mudfalt in southeast England, areas colonized by oysters were ustilized by greater numbers of Eurasion Oystercatchers and Curlews, but smaller numbers of smaller shorebiurds (Herbert et al. 2018).

Markert (2020) has published a detailed study of the structure of oyster reefs in the Wadden Sea, and comparisons with native reefs of the Blue Mussel (Mytilus edulis), as habitats for nstive and non-indigenousspecies.
B-IINoneEcological ImpactCompetition
Moderate level of community impacts (Kattegatt and Belt Seas) (Zaiko et al. 2011)
B-IINoneEcological ImpactHabitat Change
Moderate level of habitat impacts (Kattegatt and Belt Seas) (Zaiko et al. 2011).
P110Tomales BayEconomic ImpactFisheries
Commercial oyster operations, using M. gigas began in Tomales Bay in 1928, and continue to the present. Oyster culture here was intially dependent on seed imported from Japan, but now uses seed produced in US hatcheries (Barrett 1963; Conte 1996).
NEP-VNorthern California to Mid Channel IslandsEconomic ImpactFisheries
Commercial oyster operations, using M. gigas began in Tomales Bay in 1928, and continue to the present. Major locations of oyster rearing included Morro Bay, Elkhorn Slough, Drakes Estero, and Tomales Bay (Barrett 1963; Carlton 1979; Conte 1996). Culture of M. gigas continues in Morro Bay, Drakes Estero and Tomales Bay (Conte 1996). In San Francisco Bay, commercial Pacfiic Oyster rearing occurred form 1932 to 1939. Oyster culture here was intially dependent on seed imported from Japan, but now uses seed produced in US hatcheries (Barrett 1963, Conte 1996). California Pacific Oyster growers produced 1.5 million pounds of shucked meat in 1995. About 90% of Calfornia's production occurred in Drakes Estero and Humboldt Bays (Conte 1996).
P100Drakes EsteroEconomic ImpactFisheries
Commercial culture of M. gigas began in Drakes Estero in 1932 and continues to the present. Oyster culture here was intially dependent on seed imported from Japan, but now uses seed produced in US hatcheries (Barrett 1963, Conte 1996). Drakes Estero is one of the two most important oyster-growing sites in California About 90% of production occurred in Drakes Estero and Humboldt Bays (Conte 1996).
P080Monterey BayEconomic ImpactFisheries
Culture of M. gigas continued in Elkhorn Slough from 1929 to the 1980s (Barrett 1963; Conte 1996; Wasson et al. 2001)
P070Morro BayEconomic ImpactFisheries
Culture of M. gigas in Morro Bay started in 1932 and continues to the present (Barrett 1963; Conte 1996; Morro Bay National Estuary Program 2005 http://www.mbnep.org/index.php).
P090San Francisco BayEconomic ImpactFisheries
Commercial rearing of M. gigas took place in San Francisco Bay from 1932 to 1939, when the company involved went out of business (Barrett 1963).
P112_CDA_P112 (Bodega Bay)Economic ImpactFisheries
Commercial rearing of M. gigas occurred in San Francisco Bay from 1932 to 1938 (Barrett 1963, cited by Carlton 1979)
NEP-VIINoneEconomic ImpactFisheries
Crassostrea gigas has been reared in oyster farms in the Gulf of California since 1973. This oyster does not reproduce successfully here, so the operations are dependent on hatcheries (Arizpe 1996; Caceras-Martinez et al. 2007).
NEP-VIPt. Conception to Southern Baja CaliforniaEconomic ImpactFisheries
Substantial aquaculture operations for M. gigas occur in Bahia San Quitin, Baja California, Mexico (Rodriguez and Ibarra-Obando 2008).
P130Humboldt BayEconomic ImpactFisheries
Magallana gigas is reared in extensive aquaculture operations in Humboldt Bay. These began in 1953 and continue to the present. About 90% of Calfornia's production occurred in Drakes Estero and Humboldt Bays (Conte 1996).
P170Coos BayEconomic ImpactFisheries
Culture of M. gigas continues in Coos Bay to the present (Oregon Department of Fish and Wildlife http://www.dfw.state.or.us/mrp/shellfish/bayclams/about_oysters.asp)
P180Umpqua RiverEconomic ImpactFisheries
Culture of M. gigas continues in Winchester Bay (a subestuary) to the present day (Oregon Department of State Lands 2011, http://www.oregon.gov/DSL/SSNERR/docs/EFS/EFS34aquaculture.pdf?ga=t)
NEP-IVPuget Sound to Northern CaliforniaEconomic ImpactFisheries
Willapa Bay and Grays Harbor are major oyster-growing areas, producing more than 10% of the US oyster crop, through intensively managed culture (Feldman et al. 2000; Ruesink et al. 2006). A negative impact of this aquaculture operation is the use of the pesticide carbaryl to kill the mud shrimps Neotrypaea californiensis and Upogebia pugettensis, which interfere with oyster culture by burrowing and suspending sediment. The pesticide also kills juvenile Dungeness Crabs (Metacarcinus magister), English sole (Parophrys vetulus), and other commerical and sport fishery species, as well as raising general environmental concerns (Feldman et al. 2000).

In Oregon, aquaculture of M. gigas began in 1906 in Yaquina Bay, and 1940-1948 in Netarts, Tillamook, Winchester, and Coos Bays (Carlton 1979), and continues to the present day (Oregon Department of Fish and Wildlife 2011, http://www.dfw.state.or.us/mrp/shellfish/bayclams/about_oysters.asp; Oregon Department of State Lands 2011, http://www.oregon.gov/DSL/SSNERR/docs/EFS/EFS34aquaculture.pdf?ga=t).
P230Netarts BayEconomic ImpactFisheries
None
P240Tillamook BayEconomic ImpactFisheries
Magallana gigas (Pacific Oyster) are currently cultured in Tillamook Bay (Oregon Department of Fish and Wildlife 2011; http://www.dfw.state.or.us/mrp/shellfish/bayclams/about_oysters.asp).
P270Willapa BayEconomic ImpactFisheries
Willapa Bay is a major oyster-growing area, producing 10% of the US oyster crop, through intensively managed culture (Ruesink et all. 2006). A negative impact of this aquaculture operation is the use of the pesticide carbaryl to kill the mud shrimps Neotrypaea californiensis and Upogebia pugettensis, which interfere with oyster culture by burrowing and suspending sediment. The pesticide also kills juvenile Dungeness Crabs (Metacarcinus magister), English sole (Parophrys vetulus), and other commerical and sport fishery species, as well as raising general environmental concerns (Feldman et al. 2000).
NEP-IVPuget Sound to Northern CaliforniaEcological ImpactHabitat Change
Intensive oyster production has greatly altered Willapa Bay. Most of the production takes place in the intertidal zone, which was formerly mudflat. The native Olympic Oyster, O. lurida, now rare, was primarily subtidal. Oyster growth in the interitdal zone has created large areas of hard, stuctured habitat, which supports greatly increased densities of epibenthic invertebrates, incluiding mussels, scaleworms, and tube-dwelling amphipods (Ruesink et al. 2005; Ruesink et al. 2006; Hosack et al. 2006). However, the large accumulations of shell which M. gigas creates in the intertidal zone has a negetive effect on the native oyster by attracting large numbers of settling larvae of O. lurida, in the interitdal zone, where their survival is poor, acting as a recuriment sink (Ruesink et al. 2005)
P270Willapa BayEcological ImpactHabitat Change
Intensive oyster production has greatly altered Willapa Bay. Most of the production takes place in the intertidal zone, which was formerly mudflat. The native Olympic Oyster, O. lurida, now rare, was primarily subtidal. Oyster growth in the intertidal zone has created large areas of hard, stuctured habitat, which supports greatly increased densities of epibenthic invertebrates, including mussels, scaleworms, and tube-dwelling amphipods (Ruesink et al. 2005; Ruesink et al. 2006; Hosack et al. 2006). However, the large accumulations of shell which M. gigas creates in the intertidal zone has a negative effect on the native oyster by attracting large numbers of settling larvae of O. lurida, to the interitdal zone, where their survival is poor, acting as a recuriment sink (Ruesink et al. 2005).
P270Willapa BayEcological ImpactHerbivory
The greatly increased oyster biomass has resulted in an increase in filtration rate of about 25%, from 0.8 to 1.3% of the bay's volume. This is an underestimate, since it is based on harvested biomass, and excludes feral populations of M. gigas. However, oyster-rearing habitat consitutes only a small portion of Willapa Bays area (Ferraro and Cole 2007).
NEP-IVPuget Sound to Northern CaliforniaEcological ImpactHerbivory
The greatly increased oyster biomass has resulted in an increase in filtration rate of about 25%, from 0.8 to 1.3% of the bay's volume (Ruesink et al. 2006). This is an underestimate, since it is based on harvested biomass, and excludes feral populations of M. gigas.
P280Grays HarborEconomic ImpactFisheries
Grays Harbor is a major oyster-growing area, producing 10% of the US oyster crop, through intensively managed culture. A negative impact of this aquaculture operation is the use of the pesticide carbaryl to kill the mud shrimps Neotrypaea californiensis and Upogebia pugettensis, which interfere with oyster culture by burrowing and suspending sediment. The pesticide also kills juvenile Dungeness Crabs (Metacarcinus magister), English sole (Parophrys vetulus), and other commerical and sport fishery species, as well as raising general environmental concerns (Feldman et al. 2000).
P290Puget SoundEconomic ImpactFisheries
Magallana gigas has been reared in Puget Sound since 1902 in commercial operations (Carlton 1979). Commercial rearing includes bottom and raft culture in many of the Bay's inlets. However, pollution limits the extent of oyster culture. The fishery is largely dependent on hatcheries for reproduction, but some natural settlement occurs (Carlton 1979; Quayle 1969; Pauley et al. 1988; Cohen et al. 2001).
NEP-IIIAlaskan panhandle to N. of Puget SoundEconomic ImpactFisheries
Magallana gigas has been reared in Puget Sound since 1902 in commercial operations (Carlton 1979). Commercial rearing includes bottom and raft culture in many of the Sound's inlets. However, pollution limits the extent of oyster culture. The fishery is largely dependent on hatcheries for reproduction, but some natural settlement occurs (Pauley et al. 1998; Cohen et al. 2001). In British Columbia, plantings began around 1912. Fisheries gradually expanded, especially with a mass spawning in 1958, but closures due to sewage pollution in the 1960s began to limit harvests in developed areas (Quayle 1969). Since the 1990s, most culture in British Columbia has primarily used raft culture on suspended ropes (BC Shellfish Grower's Association 2011; http://bcsga.ca/about/industry-encyclopedia/oysters/). In 2005, 7,638 tonnes of Pacific oysters were produced in British Columbia at a value of $8 million CAN (Canadian department of Fisheries and Oceans 2006; http://www.dfo-mpo.gc.ca/aquaculture/shellfish-mollusque/pac_oyster-huitre-eng.htm).
NEP-IIAlaska south of the Aleutians to the Alaskan panhandleEconomic ImpactFisheries
Crassostrea gigas (Pacific Oyster) is cultured in Alaska waters, but does not reproduce. Culture is dependent on hatcheries (Hines et al. 2000; Hines et al. 2001).
NEA-IINoneEcological ImpactCompetition
On the Wadden Sea Coast of Germany, M. gigas has been settling on mussel (Mytilus edulis) beds growing on mudflats, since at least 1991, resulting in overgrowth of mussels and attached barnacles, converting mussel beds to oyster beds (Reise 1998; Baird 2012). However, year to year variation in oyster spawning and settlement, the steadier recruitment of mussels, and the poor settlement of oysters on mussels covered with the seaweed Fucus vesiculosus allow for the co-occurrence of oysters and mussels (Diederich 2005).
SA-INoneEcological ImpactHabitat Change
Oyster beds of M. gigas in Bahia Anagada in Argentina supported higher concentrations of benthic invertebrates than adjacent marsh zones. However, the overall effect of the oyster beds was small, owing to the limited amount of hard substrate for oyster settlement (Escapa 2004; Herbert et al. 2016). Tide pools on the reefs provide a new habitat for a variety of native seaweeds (Croce and Parodi 2012). In surveys at El Condor, settlement of invertebrates in oyster beds did not consistently differ from control plots (36-41 S, Mendez et al. 2015)
AUS-XNoneEconomic ImpactFisheries
Magallana gigas has ben cultured in New South Wales since 1967 (Nell 2001), although it has been regarded as a pest for competition with the native Sydney Rock Oyster (Saccostrea glomerata) (Nell et al. 2001; Krassoi et al. 2008). In the Port Jackson estuary, M. gigas outnumbered S. glomerata in the upper reaches fo the estuary (Scanes et al. 2016).
AUS-XNoneEcological ImpactCompetition
Magallana gigas overgrows and smothers the native Sydney Rock Oyster (Saccostrea glomerata) in subtidal to mid-intertidal zones, but has 80% mortality in the high intertidal zone, where S. glomerata dominates. Magallana gigas has superior growth rates to S. glomerata, but is less tolerant of abiotic stress (Krassoi et al. 2008). The larger recruits of M. gigas have greater survival than S. glomerata under various condtions of density and predation reduction (Hedge and Johnston 2014).
NZ-IVNoneEconomic ImpactFisheries
Magallana gigas is actively fished and cultured in New Zealand (Ruesink et al. 2005).
NZ-IVNoneEcological ImpactCompetition
'Following the first observation of M. gigas in Mahurangi Harbour, New Zealand in 1971, the ratio of oyster recruits rapidly changed from 1000 native Saccostrea glomerata to every M. gigas in 1972, to four exotic oyster recruits to every native recruit in 1978' (Dinamani 1991, cited by Krassoi et al. 2008). Magallana gigas has much higher growth rates and fecuundity than the native S. glomerata (Sydney Rock Oyster) (Krassoi et al. 2008).
AUS-IXNoneEconomic ImpactFisheries
Oyster culture continues in southern Tasmania, using intertidal baskets (Nell 2001).
AUS-VIINoneEconomic ImpactFisheries
Extensive oyster culture (M. gigas), using hatcheries and spat imported from Tasmania, continues in South Australia (Nell 2001).
NEP-IVPuget Sound to Northern CaliforniaEcological ImpactCompetition
Competition between the introduced Pacific Oyster (Magallana gigas) and the native Olympia Oyster (Ostrea lurida) is expected to be minimal, since M. gigas tends to settle, and is cultivated in intertidal areas, while the native oyster tends to grow in the lower intertidal and subtidal areas. However, where they do overlap, M. gigas grows much faster, and has a higher filtration rate (Ruesink et al. 2005). Competition for space occurs when M. gigas displaces native Eelgrass (Zostera marina), in culture operations (Wagner et al. 2012).
P270Willapa BayEcological ImpactCompetition
Competition between the introduced Pacific Oyster (Magallana gigas) and the native Olympia Oyster (Ostrea lurida) is expected to be minimal, since M. gigas tends to settle, and is cultivated in intertidal areas, while the native oyster tends to grow in lower intertidal and subtidal areas. However, where they do overlap, M. gigas grows much faster, and has a higher filtration rate (Ruesink et al. 2005). Competition for space occurs when M. gigas displaces native Eelgrass (Zostera marina), in culture operations (Wagner et al. 2012).
P270Willapa BayEcological ImpactParasite/Predator Vector
Parasite-Predator vector- The introduction of M. gigas has been a possible/probable vector for a number of oyster foulers or predators in Willapa Bay, including Pteropurpura (=Ocinebrellus) inornata (Japanese Oyster Drill), the parasitic copepod Mytilicola orientalis (widespread), the bryozoan Schizoporella japonica, and the tunicate Botrylloides violaceus (Carlton 1979; Cohen et al. 2001).
NEA-IINoneEconomic ImpactFisheries
In northern Europe, overfishing and pollution led to a great decline in stocks of the native Flat Oyster (Ostrea edulis). The native oyster was partially replaced by cultured seed of the Portuguese Oyster (M. angulata), imported from Portugal or Spain. However, diseases in the 1960s and 70s ended this trade, and led to searches for a new oyster. Magallana gigas was introduced into waters of the United Kingdom in 1965 (Walne and Helm 1979; Utting and Spencer 1992). Similar introductions took place in the Netherlands (in 1965), Belgium (in 1969, Kerckhof et al. 2007), Ireland (in 1969, Minchin 2007), Germany (in 1986, Reise 1998), Denmark (in 1972, Wrange et al. 2010). Initially, aquaculture was dependent on hatcheries, but natural spawning and recruitment was seen at some locations in the late 1980s to the present, with extensive oyster beds forming in the Wadden Sea (Netherlands-Germany-Denmark) (Reise 1998; Gittenberger et al. 2010; Troost 2010).

Negative impacts of fisheries include reduction of areas where fishnets can be used, declines in biomass of Blue Mussels (Mytilus edulis) and Common Cockles (Cerastoderma edule) (Troost 2010).

The expansion of Pacific Oyster aquaculture in the Netherlands, as well as the expansion of wild beds, and increasing populations of the American razor clam Ensis leei, has been associated with a decrease in yeilds of cultured mussels (Mytilus edulis) and Edible Cockles (Cerastoderma edule) (Smaal et al. 2013).
AR-VNoneEconomic ImpactFisheries
Oyster aquaculture, began in 1979, and was dependent on imported seed, and later on seed from hatcheries (Hopkins 2002; Wrange et al. 2010).
NEA-IVNoneEconomic ImpactFisheries
Magallana gigas (Pacific Oyster) was introduced after the decline of M. angulata (Potuguese Oyster) due to disease. It is intensively reared along the Atlantic coast of France (Grizel and Hèral 1993; Goulletquer et al. 2002).
NEA-VNoneEconomic ImpactFisheries
Magallana gigas (Pacific Oyster) is reared extensively in the Bay of Biscay (France-Spain) (Grizel and Héral 1991; de Montaudouin et al. 1999) and on the Atlantic coast of Spain and Portugal (Ruiz et al. 1992; Ruesink et al. 2005).
MED-IINoneEconomic ImpactFisheries
Magallanaa gigas (Pacific Oyster) is intensively cultivated in lagoons on the Languedoc coast of France, particularly the Thau lagoon (Grizel and Hèral 1991). Aquaculture is also reported on the coasts of Algeria, Spain, and Italy (Ruesink et al. 2005).
MED-INoneEconomic ImpactFisheries
Magallana gigas (Pacific Oyster) is cultivated in Morocco, and probably on the Atlantic Coast of Spain, although natural reproduction is not documented (Ruesink et al. 2005).
MED-IIINoneEconomic ImpactFisheries
Magallana gigas (Pacific Oyster) is cultivated in Italy and Tunisia (Ruesink et al. 2005; Antit et al. 2011)
MED-VIINoneEconomic ImpactFisheries
Magallana gigas (Pacific Oyster) is cultivated in Italy (Cesari and Pellizzato 1985; Ruesink et al. 2005).
WA-IVNoneEconomic ImpactFisheries
Crassostrea gigas (Pacific Oyster) is currently cultivated in several farms in Namibia and along the Atlantic coast of South Africa (Robinson et al. 2005; Ruesink et al. 2005; Haupt et al. 2010).
WA-VNoneEconomic ImpactFisheries
Magallana gigas (Pacific Oyster) is currently cultivated in several farms in Namibia and along the Atlantic coast of South Africa (Robinson et al. 2005; Ruesink et al. 2005; Haupt et al. 2010).
EA-VNoneEconomic ImpactFisheries
Mgallana gigas (Pacific Oyster) is currently cultivated in Mauritius (Ruesink et al. 2005)
MED-VNoneEconomic ImpactFisheries
Magallana gigas (Pacific Oyster) is cultivated in Israel (Ruesink et al. 2005)
SA-IINoneEconomic ImpactFisheries
Magallana gigas (Pacific Oyster) was reared in hatcheries, beginning in 1974, and farmed in southern Brazilian waters. Oysters were bred selectively for tolerance to higher temperatures (Melo et al. 2010).
P210Yaquina BayEconomic ImpactFisheries
Magallana gigas (Pacific Oyster) are currently cultured in Yaquina Bay (Oregon Department of Fish and Wildlife 2011 http://www.dfw.state.or.us/mrp/shellfish/bayclams/about_oysters.asp).
NEA-IIINoneEconomic ImpactFisheries
Magallana gigas is extensively cultured on the coast of southwestern England and Ireland (Utting and Spencer 1992; Minchin 2007)
SEP-BNoneEconomic ImpactFisheries
Crassostrea gigas is extensively reared in Chile. In 1999, 5441 tons were harvested, but reproduction is dependent on hatcheries (Castilla et al. 2005).
NEP-VNorthern California to Mid Channel IslandsEcological ImpactParasite/Predator Vector
Parasite-Predator vector- Although M. gigas has not become definitely established in central California, its introduction has been a possible/probable vector for a number of oyster foulers or predators, including Pteropurpura (=Ocinebrellus) inornata (Japanese Oyster Drill) in Tomales Bay, the parasitc copepod Mytilicola orientalis (widespread), the mussel Musculista senhousia, the bryozoan Schizoporella japonica, and the tunicates Botrylloides violaceus, Didemnum vexillum and Styela clava (Carlton 1979; Cohen and Carlton 1995; Wasson et al. 2001; de Rivera et al. 2005).
P090San Francisco BayEcological ImpactParasite/Predator Vector
Parasite-Predator vector- Although M. gigas has not become definitely established in San Francisco Bay, its introduction has been a possible/probable vector for a number of oyster foulers or predators, including, the parasitc copepod Mytilicola orientalis (widespread), the mussel Musculista senhousia, the bryozoan Schizoporella japonica, and the tunicates Botrylloides violaceus and Styela clava (Carlton 1979; Cohen and Carlton 1995).
P110Tomales BayEcological ImpactParasite/Predator Vector
Parasite-Predator vector- Although M. gigas has not become definitely established in Tomales Bay, its introduction has been a possible/probable vector for a number of oyster foulers or predators, including Pteropurpura (=Ocinebrellus) inornata (Japanese Oyster Drill), the parasitc copepod Mytilicola orientalis (widespread), the mussel Musculista senhousia, the bryozoan Schizoporella japonica, and the tunicates Botrylloides violaceus, Didemnum vexillum, and Styela clava (Carlton 1979; Cohen and Carlton 1995).
P080Monterey BayEcological ImpactParasite/Predator Vector
Parasite-Predator vector- Although M. gigas has not become definitely established in Elkhorn Slough, its introduction has been a possible/probable vector for a number of oyster foulers or predators, including the parasitc copepod Mytilicola orientalis (widespread), the mussel Musculista senhousia, the bryozoan Schizoporella japonica, and the tunicates Botrylloides violaceus and Styela clava (Carlton 1979; Wasson et al. 2001; de Rivera et al. 2005)
P070Morro BayEcological ImpactParasite/Predator Vector
Parasite-Predator vector- Although M. gigas has not become definitely established in Morro Bay, its introduction has been a possible/probable vector for a number of oyster foulers or predators, including the parasitc copepod Mytilicola orientalis (widespread), the mussel Musculista senhousia, the bryozoan Schizoporella japonica, and the tunicates Botrylloides violaceus, Didemnum vexillum, and Styela clava (Carlton 1979; Needles 2007)
NEP-IVPuget Sound to Northern CaliforniaEcological ImpactParasite/Predator Vector
Parasite-Predator vector- The introduction of M. gigas has been a possible/probable vector for a number of oyster foulers or predators on the Washington-Oregon-northern California Coast, including Pteropurpura (=Ocinebrellus) inornata (Japanese Oyster Drill) in Willapa Bay, the parasitic copepod Mytilicola orientalis (widespread), the bryozoan Schizoporella japonica, and the tunicates Botrylloides violaceus, Didemnum vexillum and Styela clava (Carlton 1979; Cohen and Carlton 1995; Boyd et al. 2002; Wonham and Carlton 2005).
P130Humboldt BayEcological ImpactParasite/Predator Vector
Parasite-Predator vector- The introduction of M. gigas has been a possible/probable vector for a number of oyster foulers or predators in Humboldt Bay, including the parasitc copepod Mytilicola orientalis (widespread), the bryozoan Schizoporella japonica, and the tunicates Botrylloides violaceus, Didemnum vexillum and Styela clava (Carlton 1979; Boyd et al. 2002).
P170Coos BayEcological ImpactParasite/Predator Vector
Parasite-Predator vector- The introduction of M. gigas has been a possible/probable vector for a number of oyster foulers or predators in Coos Bay including the bryozoan Schizoporella japonica, and the tunicates Botrylloides violaceus, Didemnum vexillum and Styela clava (Carlton 1979; Cohen and Carlton 1995; USGS Nonindigenous Aquatic Species Program 2010).
P180Umpqua RiverEcological ImpactParasite/Predator Vector
Parasite-Predator vector- The introduction of M. gigas has been a possible/probable vector for a number of oyster foulers or predators in Umpqua Bay including the bryozoan Schizoporella japonica, and the tunicates Botrylloides violaceus, Didemnum vexillum and Styela clava (Carlton 1979; Cohen and Carlton 1995; USGS Nonindigenous Aquatic Species Program 2010).
P210Yaquina BayEcological ImpactParasite/Predator Vector
Parasite-Predator vector- The introduction of M. gigas has been a possible/probable vector for a number of oyster foulers or predators in Yaquina Bay including the parasitic copepod Mytilicola orientalis, the bryozoan Schizoporella japonica, and the tunicates Botrylloides violaceus, and Styela clava (Carlton 1979; Cohen and Carlton 1995; USGS Nonindigenous Aquatic Species Program 2010).
NEP-IIIAlaskan panhandle to N. of Puget SoundEcological ImpactParasite/Predator Vector
Parasite-Predator vector: The introduction of M. gigas has been a possible/probable vector for a number of oyster foulers or predators on the Washington-British Columbia coast, including the seaweed Sargassum muticum, Pteropurpura (=Ocinebrellus) inornata (Japanese Oyster Drill), the flatworm Pseudostylochus ostreophagus, the parasitic copepod Mytilicola orientalis, the bryozoan Schizoporella japonica, and the tunicates Botrylloides violaceus, Didemnum vexillum, and Styela clava (Carlton 1979; Cohen et al. 1998; Cohen et al. 2002; Gillespie et al. 2007).
P290Puget SoundEcological ImpactParasite/Predator Vector
Parasite-Predator vector- The introduction of M. gigas has been a possible/probable vector for a number of oyster foulers or predators in Puget Sound, including Pteropurpura (=Ocinebrellus) inornata (Japanese Oyster Drill), the flatworm Pseudostylochus ostreophagus, the parasitic copepod Mytilicola orientalis (widespread), the bryozoan Schizoporella japonica, and the tunicates Botrylloides violaceus, Didemnum vexillum and Styela clava (Carlton 1979; Cohen et al. 1998; Cohen et al. 2001).
P293_CDA_P293 (Strait of Georgia)Economic ImpactFisheries
Bellingham, Padilla and Samish Bays are areas of long-standing oyster culture and harvesting (Carlton 1979; http://www.taylorshellfishfarms.com/ourStore-oysters-samish-bay).
P293_CDA_P293 (Strait of Georgia)Ecological ImpactParasite/Predator Vector
Parasite-Predator vector- The introduction of M. gigas has been a possible/probable vector for a number of oyster foulers or predators in northern Puget Sound, including Pteropurpura (=Ocinebrellus) inornata (Japanese Oyster Drill), the flatworm Pseudostylochus ostreophagus, the parasitic copepod Mytilicola orientalis (widespread), the bryozoan Schizoporella japonica, and the tunicates Botrylloides violaceus, Didemnum vexillum and Styela clava (Carlton 1979; Cohen et al. 1998; Cohen et al. 2002).
NA-ET3Cape Cod to Cape HatterasEcological ImpactParasite/Predator Vector
Parasite-Predator vector- Although C. gigas has never become established in the northwest Atlantic, the many failed introductions of C. gigas comprise a likely vector for the introduction of Haplosporidium nelsoni, the cause of the MSX disease which has severely affected the native Eastern Oyster, C. virdinica (Andrews 1980; Burreson and Ford 2004).
NEA-IINoneEcological ImpactParasite/Predator Vector
Parasite-Predator vector- The introduction of M. gigas has been a possible/probable vector for a number of oyster foulers or predators in northern European coastal waters, including the seaweed Sargassum muticum, many other macroalgal species, Pteropurpura (=Ocinebrellus) inornata (Japanese Oyster Drill), the parasitic copepod Mytilicola orientalis, and the tunicates Botrylloides violaceus, Didemnum vexillum and Perophora japonica (Eno et al. 1997; Reise et al. 1999; Wolff and Resie 2002; Gittenberger 2010). Mytilicola orientalis, on the coast of the Netherlands, infected Pacific Oysters (Magallana gigas at 2-43% frequency, but also were found in Blue Mussels (Mytilus edulis, 3-63%), Common Cockles (Cerastoderma edule, 2-13%), and Baltic Tellins (Macoma balthica, 6-7%) (Goedknegt et al. 2016).
NEA-IVNoneEcological ImpactParasite/Predator Vector
Parasite-Predator vector- The introduction of M. gigas has been a possible/probable vector for a number of oyster foulers or predators in Atlantic French waters, including the seaweed Sargassum muticum, many other macroalgal species, Pteropurpura (=Ocinebrellus) inornata, Japanese Oyster Drill, the parasitic copepod Mytilicola orientalis, and the tunicates Botrylloides violaceus, Didemnum vexillum and Perophora japonica (Eno et al. 1999; Goulletquer et al. 2002).
NEA-VNoneEcological ImpactParasite/Predator Vector
Parasite-Predator vector- The introduction of M. gigas has been a possible/probable vector for a number of oyster foulers or predators in the Bay of Biscay and the Atlantic waters of Spain and Portugal, including the seaweed Sargassum muticum, many other macroalgal species, Pteropurpura (=Ocinebrellus) inornata (Japanese Oyster Drill), the parasitic copepod Mytilicola orientalis, and the tunicates Botrylloides violaceus, Didemnum vexillum and Perophora japonica (Goulletquer et al. 2002; El Nagar et al. 2010; Afonso 2011)
MED-IINoneEcological ImpactParasite/Predator Vector
Parasite-Predator vector- The introduction and transfer of M. gigas has been a possible/probable vector for a number of oyster foulers or predators in lagoons of the western Mediterranean, including the seaweed Sargassum muticum, many other macroalgal species, the parasitic copepod Mytilicola orientalis, and the tunicate Styela clava. The culture of M. gigas has introduced 45+ species of macoalgae to the Thau lagoon (Galil 2000; Verlaque 2001; Davis and Davis 2008).
P100Drakes EsteroEcological ImpactParasite/Predator Vector
None
WA-IVNoneEcological ImpactParasite/Predator Vector
The East Pacific sea urchin Tetrapygus niger, native to Chile, was introduced with cultures of C. gigas in Alexander Bay, South Africa. Breeding populations are present, but no impacts are reported. Howver, in Chile, this species is a major grazer of kelp beds (Haupt et al. 2010).
NEA-IINoneEcological ImpactFood/Prey
Conversion of mussel (Mytilus edulis) beds in the Wadden Sea to Pacific Oyster beds may have adverse effects on some bird species which have difficulty detaching and opening oysters, particularly Common Eiders (Somateria mollissima). Other species such as European Oystercatchers (Haematopus ostralegus) and Herring Gulls (Larus argentatus) may be able to adjust feeding habits to the new prey (Scheiffarth et al. 2007; Baird 2012). Pacific oysters showed different patterns in the concentration of trace metals (lead, copper, cadmium, zinc), compared to native Blue Mussels (Mytilus edulis, potentially affecting the accumulation of these metals in the foodweb. However, shell thickness and predation rates may have a greater effect than metal concentrations on how these metals enter the food web, as C. gigas replaces M. edulus (Bray et al. 2015). Predation by the native Green Crab (Carcinus maenas dod not provide biotic resistance to M. gigas invasion, since the crabs preferred the native Blue Mussel (Mytilus edulis (Joyce et al. 2020).
NEA-IVNoneEcological ImpactHabitat Change
The formation of extensive M. gigas reefs has created a new habitat on the rocky coasts and mud habitats of Brittany. Reef formation on mud bottoms resulted in a shift from suspension feeders to carnivores among the fauna. Reefs on rock led to an increase in deposit feeders (LeJart and Hily 2011; Herbert et al. 2016). In the Bay of Mont-St.-Michel, colonization by M. gigas has damaged polychaete reefs of Sabellaria laveolata (Cognie et al. 2006; Dubois et al. 2006; Desroy et al. 2011, all cited by Herbert et al. 2011). While invasion of mudflat and mussel bed habitats altered the density and diversity of epifauna, benthic assemlages were similar between M. gigas and native Ostrea edulis communities in Brittany (Zwerschke et al. 2016; Zwerschke et al. 2018).
AUS-XNoneEcological ImpactHabitat Change
Magallana gigas on experimental plates in oysterbeds at Wanda Wanda Head, Port Stephens, grew larger than the native Saccostrea glomerata, and supported higher abundances of epibiotic organisms, but the identity of the biota on the two oyster species did not differ (Wilkie et al. 2012).
NEP-IIIAlaskan panhandle to N. of Puget SoundEcological ImpactFood/Prey
Juvenile M. gigas were a preferred food of the native Red Rock Crab (Cancer productus) in Puget Sound. Impacts on oyster populations were complicated by the fact that the crabs also fed on introduced predatory snails (Japanese and Atlantic Oyster Drills - Pteropurpurea inornata and Urosalpinx cinerea) (Grason and Miner 2012).
P290Puget SoundEcological ImpactFood/Prey
Juvenile M. gigas were a preferred food of the native Red Rock Crab (Cancer productus) in Puget Sound. Impacts on oyster populations were complicated by the fact that the crabs also fed on introduced predatory snails Japanese and Atlantic Oyster Drills (Pteropurpurea inornata and Urosalpinx cinerea) (Grason and Miner 2012).
NEA-IIINoneEcological ImpactHabitat Change
Magallana gigas, settling on an intertidal boulder field in Lough Swilly, Ireland, had complex effects on the epibenthic community. Some organisms, such as early settling stages of the polychaete Sabellaria alveolata, the gastropods Gibbula umbilicalis and Nucella lapillus, and the seaweed Fucus vesiculosus were favored on rocks with live oysters. Both living and dead oysters increased habitat complexity, but the filtration and biodepostion of oysters may have favored Fucus, adversely affecting a tunicate Ascidia conchilega through competition. While settlement of the reef-building polychaete Sabellaria was favored by oysters, long-term survival and colony formation did not occur on boulders with live or dead oysters. Habitat effects on several species appeared to be complex and unpredictable (Green and Crowe 2013a; Green and Crowe 2013b). Oysters on fouling plates reduced the settlement of the introduced barnacle Austrominius modestus, but not the native barnacle Semibalanus balanoides (Vye et al. 2017). In natural and artificial habitats, Pacific Oysters received more settlement of the inva.sive barnacle Austrominus modestus, comparted to the native limpet Patella vulgata (Firth et al. 2020). When Pacific Oysters were planted on mudflats, biodiversity increased, but when oysters were added to mussel beds, biodiversity decreased. Ammonium fluxes and benthic respiration increased with addition of oysters to both habitats, but silicate fluxes showed opposing reponses, increasing in mudflats, but decreasing in mudflats (Green and Crowe 2013a; Green and Crowe 2013b; Herbert et al. 2016). While invasion of mudflat and mussel bed habitats altered the density and diversity of epifauna, benthic assemlages were similar between M. gigas and native Ostrea edulis communities in southwest England (Zwerschke et al. 2016; Zwerschke et al. 2018).
NEA-IINoneEcological ImpactHerbivory
The expansion of Pacific Oyster aquaculture in the Netherlands, as well as the expansion of wild beds, and increasing populations of the American razor clam Ensis leei, has resulted in an increase of filtering biomass, and a decrease in phytoplanktion concentrations, and a shift towards an increassing proportion of picoplankton (very small, poorly grazed cells) (Smaal et al. 2013).
B-INoneEcological ImpactHabitat Change
Oyster reefs in Swedish west coast waters support higher species richness and biomass of benthic invertebrates than mussel beds or bare sediment (Hollander et al. 2015; Norling 2015; Herbert et al. 2016)
NEA-IINoneEcological ImpactTrophic Cascade
The expansion of Pacific Oyster aquaculture in the Netherlands has had indirect impacts on the predation of the Green Crab (Carcinus maenas on the Blue Mussel (Mytilus edulis, reducing predation on juvenile mussels, by providing refuges in the interspaces ibetween the oysters (Waser et al. 2015). Another indirect effect of M. gigas involves the effect of its parasite Mytilicola orientalis, which also infects the native Blue Mussel Mytiulus edulis. The longeer-lived planktonic larvae of this copepod are more likely to infect mussels at the top of the bed, more exposed to current, while a native trematode, with a short lived larva is more likely to infect mussels at the bottom of the reef, less exposed to current (Goeknecht et al. 2020).
MED-IINoneEcological ImpactHabitat Change
Increased filtration by Magallana gigas has improved water quality, enabling Zostera marina to grow in deeper water (Deslous-Paoli et al. 1998. cited by Herbert et al. 2016).
AUS-XINoneEcological ImpactFood/Prey
Magallana gigas is a food source for the naitve Mulberry Whelk Mulberry whelk) (Tenguella marginalba), which shows no preference between M. gigas and the native Sydney Rock Oyster (Saccostrea glomerata) (Wright et al. 2018).
MED-VIINoneEcological ImpactCompetition
Ezget-Balic et al. (2021) found significant overlap in feeding between M. gigas, and native Ostrea edulisand recommeded agianst the introduction of M. gigas to Lim Bay, Croatia.
MED-VIINoneEcological ImpactPredation
Ezget-Balic et al. (2021) found that n M. gigas had significant predaiton on and native Ostrea edilis larvare, and recommeded agianst the introduction of M. gigas to Lim Bay, Croatia.
AKAlaskaEconomic ImpactFisheries
Crassostrea gigas (Pacific Oyster) is cultured in Alaska waters, but does not reproduce. Culture is dependent on hatcheries (Hines et al. 2000; Hines et al. 2001).
WAWashingtonEcological ImpactCompetition
Competition between the introduced Pacific Oyster (Magallana gigas) and the native Olympia Oyster (Ostrea lurida) is expected to be minimal, since M. gigas tends to settle, and is cultivated in intertidal areas, while the native oyster tends to grow in lower intertidal and subtidal areas. However, where they do overlap, M. gigas grows much faster, and has a higher filtration rate (Ruesink et al. 2005). Competition for space occurs when M. gigas displaces native Eelgrass (Zostera marina), in culture operations (Wagner et al. 2012).
WAWashingtonEcological ImpactFood/Prey
Juvenile M. gigas were a preferred food of the native Red Rock Crab (Cancer productus) in Puget Sound. Impacts on oyster populations were complicated by the fact that the crabs also fed on introduced predatory snails Japanese and Atlantic Oyster Drills (Pteropurpurea inornata and Urosalpinx cinerea) (Grason and Miner 2012).
WAWashingtonEcological ImpactHabitat Change
Intensive oyster production has greatly altered Willapa Bay. Most of the production takes place in the intertidal zone, which was formerly mudflat. The native Olympic Oyster, O. lurida, now rare, was primarily subtidal. Oyster growth in the intertidal zone has created large areas of hard, stuctured habitat, which supports greatly increased densities of epibenthic invertebrates, including mussels, scaleworms, and tube-dwelling amphipods (Ruesink et al. 2005; Ruesink et al. 2006; Hosack et al. 2006). However, the large accumulations of shell which M. gigas creates in the intertidal zone has a negative effect on the native oyster by attracting large numbers of settling larvae of O. lurida, to the interitdal zone, where their survival is poor, acting as a recuriment sink (Ruesink et al. 2005)., On San Juan Island, Washington, intertidal M. gigas altered rocky shore communities by providing a light-colored substrate, decreasing substrate temperatures from a maximum of 56°C to 41°C. On average, oysters were 3.3°C cooler than surrounding rocks, and supported higher densities of limpets (4 species, Lottia strigatella, L. pelta, L. scutum, and L. digitalis). The most abundant limpet, L. strigatella was 3X more abundant on oysters than on surrounding rocks (Padilla 2010).
WAWashingtonEcological ImpactHerbivory
The greatly increased oyster biomass has resulted in an increase in filtration rate of about 25%, from 0.8 to 1.3% of the bay's volume. This is an underestimate, since it is based on harvested biomass, and excludes feral populations of M. gigas. However, oyster-rearing habitat consitutes only a small portion of Willapa Bays area (Ferraro and Cole 2007).
WAWashingtonEcological ImpactParasite/Predator Vector
Parasite-Predator vector- The introduction of M. gigas has been a possible/probable vector for a number of oyster foulers or predators in Willapa Bay, including Pteropurpura (=Ocinebrellus) inornata (Japanese Oyster Drill), the parasitic copepod Mytilicola orientalis (widespread), the bryozoan Schizoporella japonica, and the tunicate Botrylloides violaceus (Carlton 1979; Cohen et al. 2001)., Parasite-Predator vector- The introduction of M. gigas has been a possible/probable vector for a number of oyster foulers or predators in Puget Sound, including Pteropurpura (=Ocinebrellus) inornata (Japanese Oyster Drill), the flatworm Pseudostylochus ostreophagus, the parasitic copepod Mytilicola orientalis (widespread), the bryozoan Schizoporella japonica, and the tunicates Botrylloides violaceus, Didemnum vexillum and Styela clava (Carlton 1979; Cohen et al. 1998; Cohen et al. 2001)., Parasite-Predator vector- The introduction of M. gigas has been a possible/probable vector for a number of oyster foulers or predators in northern Puget Sound, including Pteropurpura (=Ocinebrellus) inornata (Japanese Oyster Drill), the flatworm Pseudostylochus ostreophagus, the parasitic copepod Mytilicola orientalis (widespread), the bryozoan Schizoporella japonica, and the tunicates Botrylloides violaceus, Didemnum vexillum and Styela clava (Carlton 1979; Cohen et al. 1998; Cohen et al. 2002).
WAWashingtonEconomic ImpactFisheries
Willapa Bay is a major oyster-growing area, producing 10% of the US oyster crop, through intensively managed culture (Ruesink et all. 2006). A negative impact of this aquaculture operation is the use of the pesticide carbaryl to kill the mud shrimps Neotrypaea californiensis and Upogebia pugettensis, which interfere with oyster culture by burrowing and suspending sediment. The pesticide also kills juvenile Dungeness Crabs (Metacarcinus magister), English sole (Parophrys vetulus), and other commerical and sport fishery species, as well as raising general environmental concerns (Feldman et al. 2000)., Magallana gigas has been reared in Puget Sound since 1902 in commercial operations (Carlton 1979). Commercial rearing includes bottom and raft culture in many of the Bay's inlets. However, pollution limits the extent of oyster culture. The fishery is largely dependent on hatcheries for reproduction, but some natural settlement occurs (Carlton 1979; Quayle 1969; Pauley et al. 1988; Cohen et al. 2001)., Bellingham, Padilla and Samish Bays are areas of long-standing oyster culture and harvesting (Carlton 1979; http://www.taylorshellfishfarms.com/ourStore-oysters-samish-bay)., Grays Harbor is a major oyster-growing area, producing 10% of the US oyster crop, through intensively managed culture. A negative impact of this aquaculture operation is the use of the pesticide carbaryl to kill the mud shrimps Neotrypaea californiensis and Upogebia pugettensis, which interfere with oyster culture by burrowing and suspending sediment. The pesticide also kills juvenile Dungeness Crabs (Metacarcinus magister), English sole (Parophrys vetulus), and other commerical and sport fishery species, as well as raising general environmental concerns (Feldman et al. 2000).
OROregonEcological ImpactParasite/Predator Vector
Parasite-Predator vector- The introduction of M. gigas has been a possible/probable vector for a number of oyster foulers or predators in Coos Bay including the bryozoan Schizoporella japonica, and the tunicates Botrylloides violaceus, Didemnum vexillum and Styela clava (Carlton 1979; Cohen and Carlton 1995; USGS Nonindigenous Aquatic Species Program 2010)., Parasite-Predator vector- The introduction of M. gigas has been a possible/probable vector for a number of oyster foulers or predators in Yaquina Bay including the parasitic copepod Mytilicola orientalis, the bryozoan Schizoporella japonica, and the tunicates Botrylloides violaceus, and Styela clava (Carlton 1979; Cohen and Carlton 1995; USGS Nonindigenous Aquatic Species Program 2010)., Parasite-Predator vector- The introduction of M. gigas has been a possible/probable vector for a number of oyster foulers or predators in Umpqua Bay including the bryozoan Schizoporella japonica, and the tunicates Botrylloides violaceus, Didemnum vexillum and Styela clava (Carlton 1979; Cohen and Carlton 1995; USGS Nonindigenous Aquatic Species Program 2010).
OROregonEconomic ImpactFisheries
Culture of M. gigas continues in Coos Bay to the present (Oregon Department of Fish and Wildlife http://www.dfw.state.or.us/mrp/shellfish/bayclams/about_oysters.asp), Magallana gigas (Pacific Oyster) are currently cultured in Yaquina Bay (Oregon Department of Fish and Wildlife 2011 http://www.dfw.state.or.us/mrp/shellfish/bayclams/about_oysters.asp)., nan, Magallana gigas (Pacific Oyster) are currently cultured in Tillamook Bay (Oregon Department of Fish and Wildlife 2011; http://www.dfw.state.or.us/mrp/shellfish/bayclams/about_oysters.asp)., Culture of M. gigas continues in Winchester Bay (a subestuary) to the present day (Oregon Department of State Lands 2011, http://www.oregon.gov/DSL/SSNERR/docs/EFS/EFS34aquaculture.pdf?ga=t)
CACaliforniaEcological ImpactParasite/Predator Vector
Parasite-Predator vector- Although M. gigas has not become definitely established in central California, its introduction has been a possible/probable vector for a number of oyster foulers or predators, including Pteropurpura (=Ocinebrellus) inornata (Japanese Oyster Drill) in Tomales Bay, the parasitc copepod Mytilicola orientalis (widespread), the mussel Musculista senhousia, the bryozoan Schizoporella japonica, and the tunicates Botrylloides violaceus, Didemnum vexillum and Styela clava (Carlton 1979; Cohen and Carlton 1995; Wasson et al. 2001; de Rivera et al. 2005)., Parasite-Predator vector- The introduction of M. gigas has been a possible/probable vector for a number of oyster foulers or predators in Humboldt Bay, including the parasitc copepod Mytilicola orientalis (widespread), the bryozoan Schizoporella japonica, and the tunicates Botrylloides violaceus, Didemnum vexillum and Styela clava (Carlton 1979; Boyd et al. 2002)., Parasite-Predator vector- Although M. gigas has not become definitely established in San Francisco Bay, its introduction has been a possible/probable vector for a number of oyster foulers or predators, including, the parasitc copepod Mytilicola orientalis (widespread), the mussel Musculista senhousia, the bryozoan Schizoporella japonica, and the tunicates Botrylloides violaceus and Styela clava (Carlton 1979; Cohen and Carlton 1995)., Parasite-Predator vector- Although M. gigas has not become definitely established in Morro Bay, its introduction has been a possible/probable vector for a number of oyster foulers or predators, including the parasitc copepod Mytilicola orientalis (widespread), the mussel Musculista senhousia, the bryozoan Schizoporella japonica, and the tunicates Botrylloides violaceus, Didemnum vexillum, and Styela clava (Carlton 1979; Needles 2007), Parasite-Predator vector- Although M. gigas has not become definitely established in Elkhorn Slough, its introduction has been a possible/probable vector for a number of oyster foulers or predators, including the parasitc copepod Mytilicola orientalis (widespread), the mussel Musculista senhousia, the bryozoan Schizoporella japonica, and the tunicates Botrylloides violaceus and Styela clava (Carlton 1979; Wasson et al. 2001; de Rivera et al. 2005), nan, Parasite-Predator vector- Although M. gigas has not become definitely established in Tomales Bay, its introduction has been a possible/probable vector for a number of oyster foulers or predators, including Pteropurpura (=Ocinebrellus) inornata (Japanese Oyster Drill), the parasitc copepod Mytilicola orientalis (widespread), the mussel Musculista senhousia, the bryozoan Schizoporella japonica, and the tunicates Botrylloides violaceus, Didemnum vexillum, and Styela clava (Carlton 1979; Cohen and Carlton 1995).
CACaliforniaEconomic ImpactFisheries
Commercial oyster operations, using M. gigas began in Tomales Bay in 1928, and continue to the present. Major locations of oyster rearing included Morro Bay, Elkhorn Slough, Drakes Estero, and Tomales Bay (Barrett 1963; Carlton 1979; Conte 1996). Culture of M. gigas continues in Morro Bay, Drakes Estero and Tomales Bay (Conte 1996). In San Francisco Bay, commercial Pacfiic Oyster rearing occurred form 1932 to 1939. Oyster culture here was intially dependent on seed imported from Japan, but now uses seed produced in US hatcheries (Barrett 1963, Conte 1996). California Pacific Oyster growers produced 1.5 million pounds of shucked meat in 1995. About 90% of Calfornia's production occurred in Drakes Estero and Humboldt Bays (Conte 1996)., Magallana gigas is reared in extensive aquaculture operations in Humboldt Bay. These began in 1953 and continue to the present. About 90% of Calfornia's production occurred in Drakes Estero and Humboldt Bays (Conte 1996)., Commercial rearing of M. gigas took place in San Francisco Bay from 1932 to 1939, when the company involved went out of business (Barrett 1963)., Culture of M. gigas in Morro Bay started in 1932 and continues to the present (Barrett 1963; Conte 1996; Morro Bay National Estuary Program 2005 http://www.mbnep.org/index.php)., Culture of M. gigas continued in Elkhorn Slough from 1929 to the 1980s (Barrett 1963; Conte 1996; Wasson et al. 2001), Commercial culture of M. gigas began in Drakes Estero in 1932 and continues to the present. Oyster culture here was intially dependent on seed imported from Japan, but now uses seed produced in US hatcheries (Barrett 1963, Conte 1996). Drakes Estero is one of the two most important oyster-growing sites in California About 90% of production occurred in Drakes Estero and Humboldt Bays (Conte 1996)., Commercial oyster operations, using M. gigas began in Tomales Bay in 1928, and continue to the present. Oyster culture here was intially dependent on seed imported from Japan, but now uses seed produced in US hatcheries (Barrett 1963; Conte 1996)., Commercial rearing of M. gigas occurred in San Francisco Bay from 1932 to 1938 (Barrett 1963, cited by Carlton 1979)

Regional Distribution Map

Bioregion Region Name Year Invasion Status Population Status
NWP-4a None 0 Native Established
NWP-3a None 0 Native Established
NWP-3b None 0 Native Established
NWP-4b None 0 Native Established
NWP-2 None 0 Native Established
NA-ET2 Bay of Fundy to Cape Cod 1949 Non-native Failed
NA-ET3 Cape Cod to Cape Hatteras 1935 Non-native Failed
CAR-I Northern Yucatan, Gulf of Mexico, Florida Straits, to Middle Eastern Florida 1941 Non-native Failed
NEP-III Alaskan panhandle to N. of Puget Sound 1902 Non-native Established
NEP-II Alaska south of the Aleutians to the Alaskan panhandle 1985 Non-native Stock
NEP-IV Puget Sound to Northern California 1928 Non-native Established
NEP-V Northern California to Mid Channel Islands 2000 Non-native Unknown
NEP-VI Pt. Conception to Southern Baja California 2000 Non-native Established
MED-II None 1964 Non-native Established
MED-III None 1988 Non-native Established
MED-VII None 1966 Non-native Established
MED-IV None 1978 Non-native Established
MED-IX None 1972 Non-native Established
NEA-V None 1971 Non-native Established
NEA-IV None 1966 Non-native Established
NEA-II None 1965 Non-native Established
NEA-III None 1989 Non-native Established
SA-I None 1982 Non-native Established
WA-IV None 1990 Non-native Unknown
WA-V None 1955 Non-native Established
SP-XXI None 1938 Non-native Established
AUS-IX None 1947 Non-native Established
AUS-VIII None 1960 Non-native Established
AUS-X None 1967 Non-native Established
AUS-XI None 1984 Non-native Established
AUS-VII None 1985 Non-native Unknown
AUS-IV None 1947 Non-native Unknown
NZ-IV None 1961 Non-native Established
SEP-B None 1997 Non-native Unknown
AR-V None 2007 Non-native Established
NEP-VII None 1973 Non-native Unknown
P130 Humboldt Bay 1953 Non-native Unknown
M130 Chesapeake Bay 1980 Non-native Failed
M040 Long Island Sound 1979 Non-native Failed
M010 Buzzards Bay 1976 Non-native Failed
P170 Coos Bay 1948 Non-native Failed
P090 San Francisco Bay 2000 Non-native Unknown
P010 Tijuana Estuary 2005 Non-native Established
P030 Mission Bay 2005 Non-native Established
P023 _CDA_P023 (San Louis Rey-Escondido) 2000 Non-native Established
P040 Newport Bay 1932 Non-native Established
P070 Morro Bay 1932 Non-native Failed
P080 Monterey Bay 1929 Non-native Failed
P100 Drakes Estero 1932 Non-native Failed
P110 Tomales Bay 1928 Non-native Failed
P112 _CDA_P112 (Bodega Bay) 1932 Non-native Failed
P210 Yaquina Bay 1906 Non-native Established
P230 Netarts Bay 1948 Non-native Unknown
P240 Tillamook Bay 1940 Non-native Unknown
P270 Willapa Bay 1928 Non-native Established
P290 Puget Sound 1902 Non-native Established
P293 _CDA_P293 (Strait of Georgia) 1905 Non-native Established
P284 _CDA_P284 (Hoh-Quillayute) 2002 Non-native Established
P286 _CDA_P286 (Crescent-Hoko) 2001 Non-native Established
P050 San Pedro Bay 2000 Non-native Established
P061 _CDA_P061 (Los Angeles) 1932 Non-native Failed
P095 _CDA_P095 (Tomales-Drakes Bay) 1955 Non-native Failed
N180 Cape Cod Bay 1949 Non-native Failed
M100 Delaware Inland Bays 1962 Non-native Failed
M070 Barnegat Bay 1935 Non-native Failed
M128 _CDA_M128 (Eastern Lower Delmarva) 1997 Non-native Failed
M120 Chincoteague Bay 1997 Non-native Failed
N040 Blue Hill Bay 1949 Non-native Failed
N050 Penobscot Bay 1975 Non-native Failed
N070 Damariscotta River 1975 Non-native Failed
NZ-VI None 2001 Non-native Unknown
SA-II None 2006 Non-native Established
P180 Umpqua River 1948 Non-native Failed
SP-XII None 1975 Non-native Failed
B-II None 2000 Non-native Established
B-I None 2005 Non-native Established
P292 _CDA_P292 (San Juan Islands) 1942 Non-native Established
MED-VIII None 1989 Non-native Established
MED-VI None 2007 Non-native Established
MED-V None 2001 Non-native Established
WA-I None 1991 Non-native Failed
EA-V None 1971 Non-native Unknown
SP-VII None 1969 Non-native Failed
SP-XVI None 1972 Non-native Failed
SP-IV None 1967 Non-native Failed
SP-XIII None 1972 Non-native Failed
SP-VIII None 0 Non-native Failed
SP-V None 1972 Non-native Failed
CAR-II None 1980 Non-native Failed
SEP-H None 1979 Non-native Failed
EAS-I None 1980 Non-native Failed
MED-I None 1966 Non-native Unknown
SEP-C None 1997 Non-native Unknown
CAR-IV None 1980 Non-native Failed
SP-IX None 1980 Non-native Failed
EAS-VI None 2003 Non-native Unknown
P280 Grays Harbor 1930 Non-native Established
P297 _CDA_P297 (Strait of Georgia) 1926 Non-native Established
P296 _CDA_P296 (Strait of Georgia) 1926 Non-native Established
SEP-I None 1980 Non-native Failed
CAR-VII Cape Hatteras to Mid-East Florida 1999 Non-native Failed
S010 Albemarle Sound 2001 Non-native Failed
S020 Pamlico Sound 2001 Non-native Failed
S030 Bogue Sound 2001 Non-native Failed
S040 New River 1999 Non-native Failed
S045 _CDA_S045 (New) 2001 Non-native Failed
NEP-VIII None 0 Non-native Unknown
P022 _CDA_P022 (San Diego) 2014 Non-native Established
SA-III None 0 Non-native Failed
P020 San Diego Bay 2013 Non-native Established
B-III None 2017 Non-native Unknown
SA-I None 1981 Non-native Established
B-IV None 2019 Non-native Unknown

Occurrence Map

OCC_ID Author Year Date Locality Status Latitude Longitude
27873 Fairey et al. 2002 2001 2001-10-10 Mission Bay Epifaunal 03 Non-native 32.7619 -117.2357
27956 Fairey et al. 2002 2001 2001-07-11 Los Angeles Epifaunal 03 Non-native 33.7684 -118.2782
32191 Introduced Species Study 2011 2011-04-20 Los Angeles-Long Beach Coast Guard Pier Non-native 33.7233 -118.2685
32401 California Department of Fish and Wildlife 2011 2011 2011-04-21 Long Beach Downtown Marina - ISS Non-native 33.7594 -118.1866

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