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:

Meretrix lusoria is native to estuaries and coastal waters of Asia from China (Hainan to the Bohai Sea), Korea, and Japan (as far north as Mutsu Bay, on the tip of Honshu; Chen et al. 2009; Chung 2007; Yamakawa et al. 2008). It co-occurs with several very similar species, particularly M. petechialis, which was introduced from China into Japan, to supplement declining stocks of M. lusoria, now rare in most Japanese coastal waters (Yamakawa and Imai 2012). Meretrix clams are heavily fished, and frequently raised in aquaculture in Asian waters (Yamakawa et al. 2008; Zhang et al. 2012). Several unsuccessful attempts were made to introduce Meretrix lusoria to West Coast waters (Carlton 1979). At least one introduction was made in Puerto Rico (USGS Nonindigenous Aquatic Species Program 2008; NOAA and Puerto Rico DRNA 2009). An introduction of M. meretrix was made in Kaneohe Bay, Hawaii, in 1926 and 1939, but did not reproduce (Carlton and Eldredge 2009).

North American Invasion History:

Invasion History on the West Coast:

Meretrix lusoria was planted in Humboldt Bay, California in 1957 and Grays Harbor, Washington (WA) around 1959. Experimental studies of this clam, which may have included laboratory work and/or plantings occurred at the Washington State Shellfish Laboratory in Quilcene, WA, on the Hood Canal, around this time (Hanna 1966; Carlton 1979).

Invasion History Elsewhere in the World:

An introduction of M. lusoria to Puerto Rico is reported to have occurred in Isleta Marina, Fajardo, Puerto Rico in 1990 (USGS Nonindigenous Aquatic Species Program 2009; NOAA and Puerto Rico DRNA 2009).


Clams of the genus Meretrix belong to a complex of many similar species, whose taxonomy is disputed. At least nine species are known from the Indo-West Pacific (Academy of Natural Sciences of Philadelphia 2012), and several of these are morphologically very similar. These clams also show considerable intraspecific variation in shell morphology and coloration. Chen et al. (2009) using sequences from mitochondrial cytochrome c oxidase subunit I gene (COI), concluded that M. lusoria and M. petechialis were juvenile synonyms of M. meretrix. However, Yamakawa et al. (2008) using allozymes and Yamakawa and Imai (2012) and Zhang et al. (2012) both using COI gene sequences, found M. lusoria and M. petechialis to be distinct, though very closely related. Zhang et al. (2012) found that M. meretrix clustered separately from M. lusoria and M. petechialis. Consequently, the specific identification of the 'Meretrix lusoria' introduced to the West Coast and Puerto Rico is uncertain.

Meretrix spp. has a triangular-oval shell, with a strongly rounded ventral margin, but fairly straight dorsal sides, peaking at the umbo. The umbo is slightly anterior of the midpoint of the shell and the anterior side of the shell drops more steeply than the posterior. The pallial sinus is shallow. Shell length in M. lusoria reaches at least 96 mm (Chung 2007). The shell has fine concentric growth lines and a relatively smooth surface. Color is highly variable, from white and brown concentric bands to fine reddish-brown or dark-brown mottling, forming dotted lines, and W-shaped markings (Yamakawa et al. 2008; description from photos in Zhang et al. 2012). Chinese and Japanese guidebooks and experts should be consulted for identification of these clams.


Taxonomic Tree

Kingdom:   Animalia
Phylum:   Mollusca
Class:   Bivalvia
Subclass:   Heterodonta
Order:   Veneroida
Superfamily:   Veneroidea
Family:   Veneridae
Genus:   Meretrix
Species:   lusoria


Cytherea formosa (G.B. Sowerby II, 1851)
Cytherea graphica (Lamarck, 1818)
Meretrix virgatula (Tomlin, 1923)
Venus lusoria (Röding, 1798)

Potentially Misidentified Species

Meretrix attenuata

Meretrix casta

Meretrix lamarckii

Meretrix lyrata

Meretrix meretrix
Australia, Yemen, India, Malaysia to China and Japan

Meretrix ovum

Meretrix petechialis
Very similar to M. lusoria, native to China-Korea, introduced to Japan, and hybridizes with M. lusoria.

Meretrix planisulcata

Meretrix sp.
Genetically detected undescribed species from Taiwan, introduced to Japan (Yamakawa and Imai 2013)



Meretrix lusoria is a mid-sized bivalve which inhabits sandy to silty bottoms of estuaries, from the mid-intertidal to about 20 meters depth (Chung 2007). Its habitats have water temperature ranges of approximately 12-30ºC and salinity ranges of 15-30 PSU (Chung 2007; Nakamura et al. 2010). Meretrix lusoria has separate sexes. Maturity occurs at 17-22 mm length and spawning occurs at 25-30ºC (Chung 2007; Nakamura et al. 2010). The larvae are planktonic and develop optimally at 27-35°C and 19-32 PSU (Numaguchi and Tanaka 1987).





Trophic Status:

Suspension Feeder



General HabitatUnstructured BottomNone
Tidal RangeSubtidalNone
Tidal RangeLow IntertidalNone
Vertical HabitatEndobenthicNone

Tolerances and Life History Parameters

Broad Temperature RangeNoneWarm temperate-Tropical
Broad Salinity RangeNonePolyhaline-Euhaline

General Impacts

Meretrix lusoria and other clams of the genus are important shellfish species in Asian waters. Meretrix lusoria has become rare in Japanese coastal waters, due to pollution, overfishing, and other unknown factors (Yamakawa et al. 2008; Zhang et al. 2012). The closely related M. petechialis, introduced from China, potentially could adversely affect M. lusoria through predation and competition (Yamakawa and Imai 2012). Attempts to introduce M. lusoria to the West Coast of the US were unsuccessful, as were introductions of M. meretrix in Hawaii (Carlton 1979; Carlton and Eldredge 2009). We have no information on success of an M. lusoria introduction in Puerto Rico (NOAA and Puerto Rico DRNA 2009). No impacts have been reported from Meretrix spp. introductions to the West Coast, Hawaii, and Puerto Rico.

Regional Distribution Map

Bioregion Region Name Year Invasion Status Population Status
NWP-3a None 0 Native Estab
NWP-2 None 0 Native Estab
NWP-3b None 0 Native Estab
NEP-IV Puget Sound to Northern California 1957 Def Failed
NEP-III Alaskan panhandle to N. of Puget Sound 1966 Def Failed
P290 Puget Sound 1966 Def Failed
P130 Humboldt Bay 1957 Def Failed
P280 Grays Harbor 0 Def Failed
CAR-IV None 1990 Def Unk
NWP-4a None 0 Native Estab
NWP-4b None 0 Native Estab

Occurrence Map

OCC_ID Author Year Date Locality Status Latitude Longitude


Academy of Natural Sciences of Philadelphia 2002-2024a Malacology Collection Search. <missing URL>

Academy of Natural Sciences of Philadelphia 2006-2014b OBIS Indo-Pacific Molluscan Database. <missing URL>

Carlton, James T. (1979) History, biogeography, and ecology of the introduced marine and estuarine invertebrates of the Pacific Coast of North America., Ph.D. dissertation, University of California, Davis. Pp. 1-904

Carlton, James T.; Eldredge, Lucius (2009) Marine bioinvasions of Hawaii: The introduced and cryptogenic marine and estuarine animals and plants of the Hawaiian archipelago., Bishop Museum Bulletin in Cultural and Environmental Studies 4: 1-202

Chen, Ai-hui; Zhao-xia, Li; Gong-neng, Feng (2009) Phylogenetic relationships of the genus Meretrix(Mollusca: Veneridae) based on mitochondrial COI gene sequences, Zoological Science 30(3): 233-239

Chung, Ee-Yung (2007) Oogenesis and sexual maturation in Meretrix lusoria (Röding 1798) (Bivalvia: Veneridae) in western Korea, Journal of Shellfish Research 26(1): 71-80

Hanna, G. Dallas (1966) Introduced mollusks of Western North America, Occasional Papers of the California Academy of Sciences 48: <missing location>

Harvard Museum of Comparative Zoology 2008-2021 Museum of Comparative Zoology Collections database- Malacology Collection. <missing URL>

Nakamura, Yasuo; Nakano, Tadashi; Yurimoto, Tatsuya; Maeno, Yukio; Koizumi, Takayoshi; Tamaki,Akio (2010) Reproductive cycle of the venerid clam Meretrix lusoria in Ariake Sound and Tokyo Bay, Japan, Fisheries Science 76: 931-941

NOAA; Departamento de Recursos Naturales y Ambientales (Puerto Rico Department of Natural and Environmental Resources) (2009) <missing title>, NOAA; Puerto Rico DRNA, San Juan PR. Pp. <missing location>

Numaguchi, K.; Tanaka, Y. (1987) Effects of temperature and salinity on growth of early young hard clam Meretrix-lusoria, Bulletin of National Research Institute of Aquaculture 11: 35-40

U.S. National Museum of Natural History 2002-2021 Invertebrate Zoology Collections Database.

USGS Nonindigenous Aquatic Species Program 2003-2024 Nonindigenous Aquatic Species Database.

Yamakawa, Ayako Yashiki; Yamaguchi, Masashi; Imai, Hideyuki (2008) Genetic relationships among species of Meretrix (Mollusca: Veneridae) in the Western Pacific Ocean, Pacific Science 62: 385-394

Yamakawa, Ayako Yashiki; Imai, Hideyuki (2012) Hybridization between Meretrix lusoria and the alien congeneric species M. petechialis in Japan as demonstrated using DNA markers, Aquatic Invasions 7(3): 327-336

Yamakawa, Ayako Yashiki; Imai, Hideyuki (2013) PCR-RFLP typing reveals a new invasion of Taiwanese Meretrix (Bivalvia: Veneridae) to Japan, Aquatic Invasions 8: in press

Zhang, Su-Ping; Wang, Hong-Xa; Xu, Feng-Shan (2012) Taxonmomic study of Meretrix (Bivalvia: Veneridae) from China's Seas, Acta Zootaxonomica Sinica 37(3): 473-479