Chesapeake Bay Introduced Species Database

Crassostrea gigas

Common name(s):
Pacific Oyster
The Pacific Oyster is native to the Indo-West Pacific and is the most widely transplanted shellfish in the world, introduced to at least 42 countries. Incredibly there are no established populations in western Atlantic waters, in spite of illegal or unofficial introductions in Atlantic waters near Chesapeake Bay and Delaware Bay. But the introduction of Pacific Oysters was considered as a possible means of replacing or supplementing native stocks of the Eastern Oyster (Crassostrea virginica), which has been devastated by disease and overharvest. Both the Pacific Oyster and the Chinese River Oyster (C. ariakensis) were investigated for possible introduction until 1998 following research in the Bay, which including the stocking of sterile oysters. But initial studies found that the Chinese River Oyster had better growth and survival under East Coast conditions than the Pacific Oyster, and so further research and political interest shifted to the Chinese River Oyster. Ironically, early plantings of the Pacific Oyster in the 1950s in Delaware Bay are one of the possible means of introduction of MSX (Haplosporidium nelsoni), one of the diseases that lead to the decline of Eastern Oysters. The Pacific Oyster was, however, successfully introduced to Puget Sound WA in 1902 to replace the Olympic Oyster (Ostreola conchaphila), which was devastated by overfishing.
Image courtesy of Paul Fofonoff.

Chesapeake Bay Status:

First Record
Regular Resident

Source Region
Native Region
Eastern Pacific Western Pacific

Vector(s) of Introduction

History of Spread:

Crassostrea gigas (Pacific Oyster) is native to the Indo-West Pacific from Pakistan to Japan and Korea, and the Phillipines, Borneo, and Sumatra (Carriker and Gaffney 1996). It is the most widely transplanted shellfish in the world, introduced to at least 42 countries (Food and Agricultural Organization 1998). Small illegal or unofficial introductions have occurred in Atlantic waters near Chesapeake Bay, but no established populations of this oyster are known in western Atlantic waters. However, introduction of C. gigas has been considered as a possible means of replacing or supplementing native stocks of C. virginica (Eastern Oyster), which has been devastated by diseases (Andrews 1980; Baker 1992; Mann et al. 1991). By 1998, research and political interest had shifted to Crassostrea ariakensis, which showed better growth and survival under East Coast conditions (National Research Council 2003).

In the Eastern Atlantic, C. gigas was imported to Marennes, France in small quantities in 1966. This was followed by a disease epizootic in C. angulata (Portuguese Oyster), then the predominant commercial species (itself imported to supplant the overfished Ostrea edulis, European Flat Oyster). Consequently, large imports of C. gigas were made to replace the lost C. angulata stocks (Andrews 1980; Gizel and Heral 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 is rare in British waters, owing to low water temperatures (Walne and Helme 1979).

In North America, C. gigas was first introduced to Puget Sound WA in 1902, following overfishing of the native Olympic Oyster ( Ostrea lurida) and unsuccessful stocking of C. virginica (Eastern Oyster). Early transplants were unsuccessful due to mortality in shipping, but after numerous subsequent imports, large-scale cultivation was underway in WA by 1928 (Chew 1979). In British Columbia, imports began in 1912, but large-scale natural spawning was not seen until 1932 (Quayle 1969). This species is now the basis of the West Coast oyster industry, with commercial harvests taking place from southern British Columbia to Tomales Bay CA (Chew 1979; Quayle 1969).

On the Atlantic Coast of North America, a number of plantings of small numbers of C. gigas have been made, either as authorized experiments, unofficially or illegally. Most of the latter two types of introductions are poorly documented.

Gulf of Mexico - An introduction of C. gigas to LA waters failed, reportedly due to heavy Polydora spp. infestations (Kavanaugh 1941).

Mid Atlantic Bight - Davis (personal communication, cited by Dean 1979) noted that 'numerous shipments were introduced into Long Island Sound at one time or another' (Dean 1979). A bushel of C. gigas was planted in Barnegat Bay NJ in the early 1930's, but failed to grow (Andrews 1980). 'An oysterman from Delaware saw impressive specimens of C. gigas at the Seattle Worlds Fair in 1962, and he had some sent to his home state for planting. The oysters were confiscated by a biologist who held them in trays in open waters in Rehoboth Bay, Del. for several years without serious mortality or apparent successful reproduction (Andrews 1980). 'Recently (1970's), C. gigas from the West Coast of North America was planted in Maryland waters by a seafood dealer, which resulted in a specific law prohibiting the species. The oysters were removed as soon as possible by scuba diving.' (Andrews 1980).

Although none of these documented introductions quite match in timing, introductions of Crassostrea gigas are considered a likely route for introduction of Haplosporidium nelsoni (MSX) to the Atlantic Coast of the United States (Andrews1980; Burreson et al. 2000; Kern 1998). The disease first appeared in lower Delaware Bay in 1958 (Ford and Haskin 1982). Morphologically similar organisms have been identified in C. gigas from Korea, Japan, and CA (Friedman 1996; Katkansky and Warner 1970; Kern 1976b) . Genetic comparisons between the Korean organism and Western Atlantic H. nelsoni suggest that the two organisms may be identical (Burreson et al. 2000).

Buzzards Bay, Cape Cod Bay - Six bushels of C. gigas seed were introduced to Barnstable Harbor in 1949. The oysters grew, some surviving for 5 years, but no spawning was observed (Dean 1979). In 1977, growth studies with C. gigas from CA were conducted in Fresh Pond, Falmouth ME, a tidal lagoon adjacent to Buzzards Bay. (The outlet of the pond was blocked during this experiment.) Spawning was observed in June 1977, but no settlement occurred (Hickey 1979).

Gulf of Maine - Growth studies on juvenile C. gigas in coastal ME waters were made from 1971 to 1973, but were stopped based on concern about ecological impacts (Dean 1979). Introduction of C. gigas is still a topic of study and dispute there.

The potential introduction of C. gigas to Chesapeake Bay began to be studied in the late 1970's as sharp decreases in oyster harvests were taking place, especailly in VA, leaving oyster packers in that state with a diminishing share of the market, as Gulf Coast and West Coast producers became increasingly important (Andrews 1980; DuPaul 1992). A comparison with other known species of Crassostrea (10- spp.) indicate that C. gigas had the widest temperature and salinity ranges for growth and reproduction. In addition, as a widely cultured species, its requirements for optimum growth were well-known (Mann et al. 1991). It was believed to be largely resistant to H. nelsoni and Perkinsus marinus (Dermo) (Andrews 1979b; Andrews 1980). Numerous culture experiments have been undertaken with diploid and triploid (sterile) C. gigas in order to assess the disease resistance of the Pacific Oyster and its adaptability to the Chesapeake Bay environment. Experiments in quarantined flumes indicate that C. 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). 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). By the late 1990s, the poor survival and performance of C. gigas in experimental trials in Chesapeake Bay, led to a loss of interest in this species. Research and political interest shifted to Crassostrea ariakensis, which appeared better adapted to local conditions. (National Research Council 2003)

However, legally sanctioned C. gigas introductions were prevented because of substantial risks to native C. virginica populations, as well as poor performance by the introduced oyster under Chesapeake bay conditions. Potential risks include (1) accidental introduction of epifaunal biota, pests, and parasites (Andrews 1980; Galtsoff 1932; Grizel and Heral 1991); (2) competition with C. virginica (Andrews 1980; Galtsoff 1932); (3) hybridization or genetic exchange (Andrews 1980; Gaffney and Allen 1992). These impacts will be discussed in more detail in the 'Community Ecology' section. Parasite and disease introductions can be minimized by following the ICES (International Council for Exploration of the Seas), using stock reared for several generations under quarantined conditions (Carlton 1992; Kern 1998. The other two types of impacts are more difficult to assess.

Although C. gigas shows strong disease resistance, trials in Chesapeake Bay suggest that this oyster was not well adapted to the local environment. In quarantined flumes, C. gigas had high non-disease mortality in summer (Barber and Mann 1994), and heavy Polydora spp. infestations (Burreson and Mann 1994; DeBrose and Allen 1996). While the species' survival ranges for temperature and salinity is broad, substantial recruitment requires salinities above 20 ppt (Mann et al. 1991). Limiting C. gigas to the lower Bay. C. gigas reared in MD waters (Deal Island, 9-16 ppt) did not grow and had meat of poor quality (Krantz 1992). Finally, C. gigas is generally regarded as inferior to C. virginica in texture and flavor (DuPaul 1992).

In 1993, an experimental planting of 300 triploid C. gigas was made in the York River VA (Mann and Burreson 1994). The oysters were removed when 19% of them were found to have reverted to a diploid/triploid state. The cause and significance of this reversion are currently under study (Gottlieb and Schweighofer 1996). Further introductions are unlikely until this problem is resolved. Even in VA, which was likely to benefit most from C. gigas introductions, there was broad support among oyster producers and packers only for the introduction of sterile animals (DuPaul 1992). Deliberate, legally sanctioned establishment of reproducing populations thus does not appear to be an immediate prospect, although illegal planting remains a possibility. After 1998, when triploid C. ariakensis showed good survival and rapid growth in Chesapeake Bay, interest in C. gigas diminished (National Research Council 2003).

History References - Andrews 1979b; Andrews 1980; Baker 1992; Barber 1996; Barber and Mann 1994; Baker 1992; Burreson et al. 2000;; Carlton 1992; Carriker and Gaffney 1996; Chew 1979; Dean 1979; DeBrose and Allen 1996; DuPaul 1992; Food and Agricultural Organization 1998; Friedman 1996; Gaffney and Allen 1992; Galtsoff 1932; Gottlieb and Schweighofer 1996; Grizel and Heral 1991; Hickey 1979; ; Katkansky and Warner 1970; Kavanaugh 1941; Kern 1976b; Kern 1998; Krantz 1992; Lipton et al. 1992; Mann and Burreson 1994; Mann et al. 1991; Quayle 1969; Walne and Helme 1979

Invasion Comments:

Population Status - Crassostrea gigas (Pacific Oyster) has had several failed, poorly documented introductions in the Chesapeake Bay region, as well as at least one legally sanctioned experimental introduction of sterile individuals (Mann and Burreson 1994). However establishment of reproducing populations, or planting of sterile triploid oysters on a commercial scale has not been accomplished in Chesapeake Bay or elsewhere on the Atlantic Coast of North America (Gottlieb and Schweighofer 1996; Mann et al. 1991)

This data was last modified on Friday, March 18th, 2011.
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