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Exotic Introductions into BC Marine Waters:
Major Trends

Mudflat snail (Batillaria attrementaria), photo by Brian Klinkenberg.


Michael Waldichuk, Philip Lambert, and Brian Smiley

Extracted from Biodiversity in British Columbia 1994,
with permission (see below for details).

Editor's Note: This is an historical article and many studies on introduced species have been conducted since 1994.

The entry of exotic species into Canada's Pacific marine ecosystem has been, as far as we know, related almost entirely to the introduction and maintenance of Japanese and Atlantic oysters for commercial production.  The transplant of the hardy Japanese (now called Pacific) oyster (Crassostrea gigas) as early as 1914 led to this species becoming the mainstay of the oyster industry in British Columbia.  However, the Pacific oyster cannot successfully sustain populations in coastal BC waters because water temperatures are usually too low for reproduction.  Pacific oyster seed (spat) is, therefore, being imported regularly from Japan. 

It is mainly in association with the imported oyster spat that six species of bivalves, seven species of snails (gastropods), four polychaete worm species and assorted other invertebrates have accidentally been introduced into BC coastal waters (Table 1).  Most have remained fairly localized in their distribution, which is particularly fortunate in the case of the gastropod species that prey on oysters.  These nuisance species include:  the Japanese drill (Ocenebra japonica [now Ceratostoma inornatum]) introduced into Canada and U.S. Pacific waters as early as 1928; Purpura (Mancinella) clavigera found in Ladysmith Harbour in 1951; and Batillaria cumingi (now Batillaria attramentaria ), a Japanese oyster seed in Boundary Bay, Ladysmith, Crofton, Fanny Bay and Comox. 

Gastropod predators introduced into Boundary Bay with the Atlantic oyster include the eastern oyster drill (Urosalpinx cinerea) and the eastern mud snail (Nassarius obsoletus)--both of which survived in Boundary Bay but apparently had not spread to other parts of the coast by 1964 (Quayle, 1964).  This latter species now occurs from B.C. to central California (Ricketts et al., 1985). 

Some species inadvertently introduced with foreign oysters have spread widely and contributed to commercial production in British Columbia.  The soft-shell clam (Mya arenaria) generally is believed (not unanimously) to have been introduced with plantings of Crassostrea virginica in San Francisco Bay around 1807, and then migrated northward.  The Manila (or Japanese) little neck clam (Tapes philippinarum [now Venerupis philippinarum]) was first observed in Ladysmith Harbour in 1936, apparently introduced with Japanese oyster seed.  It reproduced and spread rapidly and, by 1941, became included with the native Little Neck Clam (Protothaca staminea) in the commercial catch.  The so-called Japweed seaweed (Sargassum muticum) is now also believed to have been introduced with Japanese oyster seed.  Now part of the B.C. coastal ecoystem, this seeweed is used by herring as a substrate for egg laying, but is a nuisance to oyster growers and boaters.  Another immigrant from Japan, the parastic copepod, Mytilicola orientalis, now occurs in the intestines of oysters and muscles from B.C. to California (Rickets et al. 1985).

Attempts to introduce the Atlantic lobster (Homarus americanusi) to Canada's Pacific coast date back to the late 19th century.  Intensive experimentation on such a transplantation was conducted during the 1960's in Fatty Basin on the west coast of Vancouver Island;  all transplant attempts failed.

Table 1. Marine Plants and Animals Introduced into BC.

(Published reference given in brackets)


Gelidium vagnum (Renfrew et al. 1989)

Sargassum muticum (DeWreede 1983)

Lomentaria hakodatensis (South 1969)

Vascular Plants

Zostera japonica (Harrison et al. 1982)


Microciona prolifera (Kozloff 1987)

Halichondria bowerbanki (Kozloff 1987)


Haliplanella luciae (Carl and Guiguet 1957)

Flat Worms

Pseudostylochus ostreophagus (Quayle 1964)


Polydora ligni (Hobson and Banse 1981)

Streblospio benedicti (Hobson and Banse 1981)

Pionosyllis uraga (Fournier and Levings 1982)

Tharyx tesssalata (Fournier and Levings 1982)


Mya arenaria (Quayle 1964)

Musculus senhousia (Bernard 1983)

Tapes philipinarum (Quayle 1964; Bourne 1982)

Gemma gemma (Bernard 1983)

Teredo navalis (Quayle 1964)

Trapezium liratum (Quayle 1964)

Crassostrea gigas (Quayle 1964)

Crassostrea virginica (Quayle 1964)


Ocenebra jaonica (Quayle 1964)

Nassarius obsoletus (Quayle 1964)

Purpura clavigera (Quayle 1964)

Cerastostoma inomatum (Quayle 1988)

Urosalpinx cinerea (Quayle 1964)

Batillaria cumingi (Quayle 1964)

Crepidula fornicata (Kozloff 1987)


Homarus americanus

Mytilicola orientalis

Limnoria tripunctata


Salmo salar (Carl and Guiget 1957)

An unsuccessful attempt was made in 1905 to introduce Atlantic salmon (Salmo salari) into B.C. coastal waters.  However, some individuals of this species, presumably escapees from salmon farms, have recently been caught by commercial fishers.

To our knowledge, there has not yet been a comprehensive study of introductions associated with ships in Vancouver or Seattle harbours. Carlton (1985) reviewed the introduction of foreign organisms world-wide, via the ballast tanks of freighters.  In San Francisco harbour, he found that almost 100 exotic marine invertebrates had been introduced from other parts of the world, presumably as fouling organisms on hulls of ships, in their ballast tanks, or with oyster introductioins (Carlton 1979).  We do not have comparable data for B.C. waters, but we do know that wood-boring animals introduced to these waters by vessels and other means include the Atlantic shipworm (Teredo navalis) and the crustacean woodborer (Limnoria tripunctata) (Carl and Guiget, 1957).

[Editor's Note: research on this is now underway via the Canadian Aquatic Invasive Species Network.]

Japanese drill (Ceratostoma inornatum), photo by Aaron Baldwin.

Management Responses

Introduction of exotic species is controlled by regulations under the Fisheries Act.  The oyster seed inspection system was properly organized and working by 1940.  The introduction of exotic species with oyster seed appears to have been well controlled since then, but most introductions had already occurred prior to 1940. 

Carlton (1989) writes about the conventions governing the introduction of exotic marine species through shipping practises, especially the dumping of ballast and the use of antifouling agents on hulls.  According to him there is a series of international policies and conventions with clauses that pertain to the control of introductions.  These policies and conventions include the 1973 Code of Practice of the International Council for the Exploration of the Sea, the 1973 position paper of the American Fisheries Society, the 1984 recommendation of the Council of Europe, and the Convention on the Law of the Sea.  Carlton (1989) maintains that, although these clauses have brought international attention to the problem of alien introductions, most biologists have never heard of them and most of them are not really enforceable.


Introduced species have out-competed some local populations of native species, but no indigenous marine species seem to have become extinct as a consequence of introductions.  However, in the southern end of San Francisco Bay, introduced species dominate benthic communities.  We should expect similar introductions to occur in Vancouver because it is an international port. So far, introduced populations seem to be confined to bays and harbours and not to open coast, but they should be monitored for changes.  In general, human-caused extinctions have been comparatively rare in the sea, except for large birds and mammals (Vermeij 1986). 


Colin Levings, Fisheries and Oceans Canada, reviewed the manuscript.

Original citation for this article: Waldichuk, M., P. Lambert and B. Smiley. 1994. Exotic Introductions into BC Marine Waters.  Pp. 220-223.  In Biodiversity in British Columbia, edited by L. Harding and E. McCullum. Ottawa: Environment Canada.   Reproduced with the permission of the Minister of Public Works and Government Services Canada, 1998, and with permission of Environment Canada.


Bernard, F. R. 1969.  Parasitic copepod Mytilicola orientalis in British Columbia Bivalves.  J. Fish. Res. Bc. Canada 26: 190-191.

Bernard, F. R. 1983.  Catalogue of the Living Bivalvia of the Eastern Pacific Ocean:  Bering Strait to Cape Horn.  Department of Fisheries and Oceans.  Ottawa.  102 p.  (Canadian Special Publications of Fisheries and Aquatic Sciences 61).

Bourne, N. 1982.  Distribution, reproduction and growth of Manila Clam, Tapes philippinarum (Adams and Reeves), in British Columbia.  J. Shellfish Res. 2:  47-54.

Carl, G. C. and C. J. Guiget.  1957.  Alien Animals in British Columbia.  K. M. MacDonald, Queen's Printer, Victoria, BC.

Carlton, J. T.  1985.  Transoceanic and interoceanic dispersal of coastal marine organisms:  the biology of ballast water.  Oceanography and Marine Biology:  An Annual Review  23:  313-371.

to be continued.....

Please cite these pages as:

Author, date, page title. In:   Klinkenberg, Brian. (Editor) 2023. E-Fauna BC: Electronic Atlas of the Fauna of British Columbia []. Department of Geography, University of British Columbia, Vancouver. [Date Accessed]

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