Invasion History

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

General Invasion History:

Magallana sikamea was described from the Ariake Sea, on the southern coast of Kyshu, Japan. Molecular surveys have extended its range through the East China Sea to the south coast of Korea (Hong et al. 2012), Taiwan (Chuang et al. 2014) China and Hainan Island (Wang et al. 2013). Its recent (2011) discovery in the Seto Inland Sea could be the result of natural dispersal or human transplantation (Hamaguchi et al. 2013). This species has been spawned in hatcheries and cultivated on the West Coast of the US and Mexico without any documented natural reproduction (Hedgecock et al. 1993; Coan et al. 2000; Washington Sea Grant 2002; Caceres-Martinez et al. 2012). Plantings of this oyster in Atlantic France, Brazil, and Tasmania have not resulted in reproduction or in successful commercial culture (Simoes Ramos et al. 1986; English et al. 2000; Goulletquer et al. 2002).

North American Invasion History:

Invasion History on the West Coast:

Dates of the introduction of Magallana sikamea to the West Coast of the US are uncertain, because this oyster was long regarded as a variety or subspecies of the Pacific Oyster (M. gigas). Websites of some oyster farms state that culture started in the 1940s, but Hedgecock et al. (1993) trace the two major cultured stocks to two separate importations in the 1970s. One was by the Oregon Oyster Company, which reared the oysters at the Hatfield Marine Science Center in Newport, Oregon (OR). Some oysters from this importation were later reared by Taylor Shellfish Inc. in Puget Sound, Washington (WA). This stock included oysters with M. sikamea morphology and genotypes, but also many hybrids with M. gigas morphology. A second stock was imported around the same time by the Coast Oyster Co. and initially reared in Humboldt Bay, California (CA). Of the 29 individuals examined, one was M. gigas by morphology and genotype. Reproduction of both stocks was/is dependent on hatcheries and apparently limited by low water temperature (Washington Sea Grant 2013). However, natural reproduction is not known even in the warm waters of Pacific Mexico, where M. sikamea is cultured (Cáceres-Martinez et al. 2012). Currently, the Kumamoto Oyster is less widely cultured on the West coast than M. gigas, but it is highly regarded for good flavor and a good quantity of meat despite its small size. It also benefits from the absence of spawning during the summer months, when other oysters are spawning and less desirable (Washington Sea Grant 2013). In the USA, the Kumamoto Oyster is currently cultured in Puget Sound, WA; Yaquina Bay, OR; Humboldt Bay, CA; Tomales Bay, CA; and Morro Bay, CA (Hedgecock 1993; Moore et al. 2014). It is also reared in Bahia San Quintin, Mexico (Cáceres-Martinez et al. 2012). There is no reported evidence for reproduction of M. sikamea in North American waters.

Invasion History Elsewhere in the World:

In 1947, 5000 Magallana sikamea were sent to Pittwater, Tasmania from Kumamoto, Japan, together with a much larger shipment of Pacific Oysters. In the 1990s, no evidence of M. sikamea alleles was found in the population, which was apparently all C. gigas (English et al. 2000). An introduction in La Tremblade, France on the Bay of Biscay, in 1994, did not result in an established population (Goulletquer et al. 2002). We found no mention of this oyster being cultured in France. Another experimental trial was made with this oyster in Todos Santos Bay, Brazil (Simoes Ramos et al. 1986), again with no reports of subsequent culture.


Magallana sikamea resembles other oysters in having unequal valves and an irregular shape. It is closely related to the Pacific Oyster C. gigas, but has a very deep left valve (unattached to a surface), with three or more broad radial ridges. The right valve is flattened, but usually corrugated. The shell looks triangular in side view. The shell is relatively smooth, with obscure lamellae on the margin and broad radial ribs. The adductor scar is dark purple. This oyster is relatively small, but deeply cupped reaching a maximum size of about 60 mm. Description based on Coan (2000) and Coan and Valentich-Scott (2007).

Magallana sikamea was formerly considered a subspecies of M. gigas, but is now considered a full species. Because oysters can be broadly distributed across substrates and growth conditions, molecular methods are needed for certain identification. Hybridization with M. gigas has occurred among cultured stocks on the West Coast of the US (Hedgecock et al. 1993). The two species can hybridize, but only C. gigas sperm and M. sikamea eggs produce viable offspring; the inverse cross is unsuccessful (Banks et al. 1995). In Asian waters, where many species of Crassostrea co-occur, molecular studies have expanded the known range of M. sikamea (Hedgecock et al. 1999; Reece et al. 2001; Hong et al. 2012; Wang et al. 2013; Chuang et al. 2012).

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). 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). Currently, the genus name Magallana is largely used in European literature. Recent genetic analysis by Salvi and Mariottini (2020) supports the transfer of the Inod-West Pacific 'Crassostrea' to the new genus Magallana.


Taxonomic Tree

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


Ostrea gigas var. sikamea (Amemiya, 1928)
Crassostrea gigas 'kumamoto' (None, None)
Magallana sikamea (Salvi & Marriotini, 2016)

Potentially Misidentified Species

Crassostrea virgnica
Eastern Oyster

Magallana gigas
Pacific Oyster

Magallana ariakensis
Suminoe Oyster, cultured on the West Coast, with experimental introductions of triploids on the East Coast



Magallana sikamea (Kumamoto Oyster) was long considered a subspecies of the Pacific Oyster (M. gigas, found in warmer waters of southern Japan and China. It differs in temperature and salniity requirements for reproduction, prefeering temperatures of 24-28 C and 20-25 (PSU). The temperature requirements limit its establishment in the wild on the West Coast (Robinson 1992).

In China, it was found on rocky shores anx hard structures in the low-to-mid intertidal zone (Wang et al. 2013).


General HabitatRockyNone
General HabitatOyster ReefNone
General HabitatMarinas & DocksNone
Salinity RangePolyhaline18-30 PSU
Salinity RangeEuhaline30-40 PSU
Tidal RangeSubtidalNone
Tidal RangeLow IntertidalNone
Vertical HabitatEpibenthicNone

Tolerances and Life History Parameters

Maximum Temperature (ºC)28Robinson 1992, highest tested
Minimum Reproductive Temperature20Robinson 1992
Maximum Reproductive Temperature28Highest tested (Robinson 1992)
Minimum Reproductive Salinity20Robinson 1992;
Maximum Reproductive Salinity35Xu et al. 2011
Maximum Length (mm)60Coan et al. 2000
Broad Temperature RangeNoneWarm temperate-Subtropical
Broad Salinity RangeNonePolyhaline-euhaline

General Impacts

Magallana sikamea (Kumamoto Oyster) does not have documented breeding populations in North America, but is reared in culture. Despite its small size, it has a niche market in the United States for its cupped shape and unique flavor (Wang et al. 2013).

Regional Impacts

P290Puget SoundEconomic ImpactFisheries
Succesful hatchery-based culture (Washington Sea Grant 2002)
NEP-IIIAlaskan panhandle to N. of Puget SoundEconomic ImpactFisheries
Succesful hatchery-based culture (Washington Sea Grant 2002)
P210Yaquina BayEconomic ImpactFisheries
Succesful hatchery-based culture (Robinson 1994)
P130Humboldt BayEconomic ImpactFisheries
Succesful hatchery-based culture (Hedgecock et al. 1993; Moore et al. 2014)
NEP-VNorthern California to Mid Channel IslandsEconomic ImpactFisheries
Succesful hatchery-based culture (Hedgecock et al. 1993; Moore et al. 2014).
P110Tomales BayEconomic ImpactFisheries
Succesful hatchery-based culture (Hedgecok 1992; Moore et al. 2014)
P070Morro BayEconomic ImpactFisheries
Succesful hatchery-based culture (Hedgecock et al. 1993; Moore et al. 2014)
NEP-VIPt. Conception to Southern Baja CaliforniaEconomic ImpactFisheries
Succesful hatchery-based culture (Hedgecock et al.1993; Moore et al. 2014).

Regional Distribution Map

Bioregion Region Name Year Invasion Status Population Status
NEP-III Alaskan panhandle to N. of Puget Sound 1991 Def Failed
P290 Puget Sound 1991 Def Failed
NEP-IV Puget Sound to Northern California 1991 Def Failed
P143 _CDA_P143 (Smith) 2005 Def Failed
P130 Humboldt Bay 1991 Def Failed
NEP-V Northern California to Mid Channel Islands 2005 Def Failed
P110 Tomales Bay 2005 Def Failed
P070 Morro Bay 0 Def Failed
NEP-VI Pt. Conception to Southern Baja California 1970 Def Failed
NWP-3a None 0 Native Estab
NWP-3b None 2011 Crypto Estab
NWP-2 None 0 Native Estab
NEA-V None 1994 Def Failed
AUS-IX None 1947 Def Failed
P210 Yaquina Bay 0 Def Failed
SA-III None 1980 Def Failed
P270 Willapa Bay 0 Def Failed

Occurrence Map

OCC_ID Author Year Date Locality Status Latitude Longitude


Banks, M. A.; Goldrick, D. J.; Borgeson, W.; Hedgecock, D. (1994) Genetic incompatibility and genetic divergence of Pacific and Kumamoto Oysters, Crassostrea gigas amd C. sikamea), Marine Biology 121: 127-135

Cáceres-Martínez, Jorge; Vásquez-Yeomans, Rebeca; Guerrero-Rentería, Yanet (2012) Early gametogenesis of Kumamoto oyster (Crassostrea sikamea ), Hidrobiológica 22(2): 181-184

Calder, Dale R. (2019) On a collection of hydroids (Cnidaria, Hydrozoa) from the southwest coast of Florida, USA, Zootaxa 4689(1): 1-141

Carriker, Melbourne R.; Gaffney, Patrick M. (1996) The Eastern Oyster Crassostrea virginica, Maryland Sea Grant, College Park MD. Pp. <missing location>

Chávez-Villalba, Mazón-Suástegui, José M.;; Maeda-Martínez, Alfonso N. ,García-Morales, Ricardo; Lodeiros, César (2021) Tropical and subtropical Ostreidae of the American Pacific: fisheries, aquaculture, management, and conservation, Journal of Shellfish Research 40(2): 239-253

Chávez-Villalba, Jorge; Arreola-Lizárraga, Alfredo; Burrola-Sánchez, Sara; Hoyos-Chairez, Francisco (2009) Growth, condition, and survival of the Pacific oyster Crassostrea gigas cultivated within and outside a subtropical lagoon, Aquaculture 300: 128-136

Chuang, Shih-Chang; Hsiao,Sheng-Tai; Huang, Min-Yu; Wu, Chi-Lun (2012) New record of Kumamoto Oyster Crassostrea sikamea (Amemiya, 1928) in Matsu, Taiwan, Journal of Taiwan Fisheries Research 22(1): 15-22

Coan, Eugene V.; Valentich-Scott, Paul (2007) The Light and Smith Manual: Intertidal Invertebrates from Central California to Oregon, University of California Press, Berkeley CA. Pp. 807-859

Coan, Eugene V.; Valentich-Scott, Paul; Bernard, Frank R. (2000) <missing title>, Santa Barbara Museum of Natural history, Santa Barbara CA. Pp. <missing location>

English, L. J.; Maguire, G. B.; Ward, R. D. (2000) Genetic variation of wild and hatchery populations of the Pacific oyster, Crassostrea gigas Thunberg, in Australia, Aquaculture 187: 283-298

Goulletquer, Philippe; Bachelet, Guy; Sauriau, Pierre; Noel, Pierre (2002) Invasive aquatic species of Europe: Distribution, impacts, and management., Kluwer Academic Publishers, Dordrecht. Pp. 276-290

Hamaguchi, Masami; Shimabukuro, Hiromori; Kawane, Masako; Hamaguchi, Tomoki (2013) A new record of the Kumamoto oyster Crassostrea sikamea in the Seto Inland Sea, Japan, Marine Biodiversity Records 6: e16

Hedgecock, D.; Li, G.; Banks, M. A.; Kain, Z. (1999) Occurrence of the Kumamoto oyster Crassostrea sikamea in the Ariake Sea, Japan, Marine Biology 133: 65-68

Hedgecock; Dennis; Banks, Michael A.; McGoldrick, Daniel J. (1993) The status of the Kumamoto Oyster Crassostrea sikamea in U. S. Commercial broodstocks, Journal of Shellfish Research 12(2): 215-222

Hegazi, Muhammad Mosaad (2006) Distribution of the invasive species Caulerpa prolifera along the coasts of the suez canal, egyp, Catrina 1(2): 31-35

Hong, Jae-Sang; Sekino, Masashi; Sato, Shinichi (2012) Molecular species diagnosis confirmed the occurrence of Kumamoto oyster Crassostrea sikamea in Korean waters, Fisheries Science 78: 259-267

Moore, James D.; Juhasz, Christy I.; Robbins, Thea T. (2011) A histopathology survey of California oysters, California Fish and Game 97(2): 68-83

Reece, K. S., Bushek, D., Hudson K. L. & Graves, J. E. (2001) Geographic distribution of Perkinsus marinus genetic strains along the Atlantic and Gulf coasts of the USA., Marine Biology 139: 1047-1055

Robinson, Anja (1992) Gonadal cycle of Crassostrea-gigas Kumamoto (Thunberg) in Yaquina Bay, Oregon and optimum conditions for broodstock oysters and larval culture, Aquaculture 106(1): 89-97

Simoes Ramos, Maria Indaya; Nascimento, Iracema Andrade; de Loyola e Silva, Jayme (1986) The comparative growth (and) survival of Pacific Oyster (Crassostrea gigas) Thunberg, G. gigas Kumamoto) and Mangrove Oyster (C. rhizophorae) in Todos o Santos, Brazil, Ciencia e Cultura 38(9): 1604-1615

Wang, Haiyan; Qian, Lumin; Wang, Aimin; Guo, Ximing (2013) Occurrence and distribution of Crassostrea sikamea (Amemiya 1928) in China, Journal of Shellfish Research 32(2): 439-446

Washington Sea Grant (2013) <missing title>, Washington Sea Grant, <missing place>. Pp. <missing location>

Xu, Fei; Guo, Ximing; Li, Li; Zhang, Guofan (2011) Effects of salinity on larvae of the oysters Crassostrea ariakensis, C. sikamea and the hybrid cross, Marine Biology Research 7(8): 796-803