Taxonomy

Crassostrea gigas | Portuguese Oyster

Distribution

Status

Conservation status

Not Assessed

Native status

Non-native

First reported in the wild

1973

Invasiveness

Invasive species - risk of High Impact

Irish status

Present in the wild

Introduction pathways - 1

Release in Nature

Introduction pathways subclass - 1

Aquaculture/Mariculture

Invasive score

19

NAPRA Ireland risk assessed

No

Species Biology

Identification

Filter feeding, marine bivalve, similar in apperance to the European oyster (Ostrea edulis), it has two elongated valves of varying shapes and sizes, 8-31cm in length, attached to the substrate by one of valve (Gollasch & Minchin, 2009).

Ecology

As filter feeders oysters remove particles of organic matter from the water column and producing pseudofaceaes that then settles on the surrounding substrate (Forrest et al., 2009). This can lead to an increase in organic and silt content of the underlying sediment, while also reducing the depth of the oxygenated layer, though these effects are thought to be small scale and isolated to the area immediately surrounding the oyster cultivation (Nugues et al., 1996). Generally filter feeding organisms are thought to impact negatively on macroalga through habitat alteration and competition and phyto- and zoo-plankton through predation, while benefitting mobile species (Thomsen et al., 2014).

Habitat

Marine

Reproduction

Broadcast spawners with planktonic larvae.

Pathway and vector description

Pacific oyster farming began in Ireland in 1973 and has since expanded (Minchin, 2007). 'Feral' populations of oysters have begun to spread from farm locations but exact extent of the spread and whether it is localised to areas with aquaculture is unknown (Kochmann et al., 2013).

Mechanism of impact

Competition, Bio-fouling, Other

Broad environment

Marine

Habitat description

Marine benthic organism that attaches to any hard surface, found from the lower intertidal down to 40m (Gollasch & Minchin, 2009).

Species group

Invertebrate

Native region

Temperate Asia

Similar species

European oyster (Ostrea edulis) 

Distribution

World distribution(GBIF)

Irish distribution

Established - Widespread. Widely cultivated in Ireland (Minchin, 2007) but it is unclear how widespread recruitment to the 'feral' population of Pacific oysters, is other than in Lough Foyle where the cultivated oysters have been demonstrated to be genetically distinct from the wild oysters (Kochmann et al., 2012).

Native distribution

Native to the Pacific North west (Gollasch & Minchin, 2009).

Temporal change

Date of first record category

1971-1980

Fifty year date category

1951-2000

Records submitted to Data Centre in 2024

The following map is interactive. If you would prefer to view it full screen then click here.

How can you help

Report any sightings to the National Biodiversity Data Centre.

Further information

Delivering Alien Invasive Species In Europe (DAISIE) project list this as one of the 100 Worst Invaders in Europe.

References

Publications

Forrest, B. M., Keeley, N. B., Hopkins, G. A., Webb, S. C., & Clement, D. M. (2009). Bivalve aquaculture in estuaries: review and synthesis of oyster cultivation effects. Aquaculture, 298(1), 1-15.

Gollasch, S. & Minchin, D. (2009). Crassostrea gigas (Thunberg), Pacific (giant) oyster (Ostreidae, Mollusca). In: Handbook of Alien Species in Europe DAISIE, Drake, J.A. (ed) . Springer Series in Invasion Ecology, Springer.

Kochmann, J., Carlsson, J., Crowe, T. P., & Mariani, S. (2012). Genetic evidence for the uncoupling of local aquaculture activities and a population of an invasive species—a case study of Pacific oysters (Crassostrea gigas). Journal of Heredity, 103(5), 661-671.

Minchin, D. (2007) A checklist of alien and cryptogenic aquatic species in Ireland. Aquatic Invasions, 2(4), 341-366.

Nugues, M. M., Kaiser, M. J., Spencer, B. E., & Edwards, D. B. (1996). Benthic community changes associated with intertidal oyster cultivation. Aquaculture Research, 27(12), 913-924.

Thomsen, M.S., Byers, J.E., Schiel, D.R., Bruno, J.F., Olden, J.D., Wernber, T., & Silliman, B.R. (2014) Impacts of Marine invaders on bioidversity depends on trophic position and functional similarity. Marine Ecology Progress Series, 495:39-47.


CABI Datasheet

DAISIE Factsheet

Global Invasive Species Database

Images