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Pacific oyster, Crassostrea gigas
Overview
.
Short description of Crassostrea gigas, Pacific oyster
Variable and irregular in appearance. Off-white to yellow or bluish grey in colour, often
with deep purple patches. Grows up to 30 cm in length with a teardrop shape and
rough shell. The right valve is deeply cupped with six or seven bold ribs; the left valve
is flat or slightly convex.
Description of Crassostrea gigas, Pacific oyster status in GB
Farmed at several locations around the GB coast and estuaries. Escapees have
established populations in various locations in the south of England.
Author's name:
Natalie Sweet
Last updated:
January 6th, 2012
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H a b i t a t s u m m a r y : Crassostrea gigas, Pacific oyster
Lives permanently attached to any hard substrate in intertidal and shallow subtidal
zones of estuaries and coastal waters. In muddy or sandy areas Pacific oysters will
settle on small rocks, shells or other oysters and can create reefs by cementing their
shells to each other, forming dense layers.
Overview table
Environment:
Marine and Freshwater
Species status:
Non-Native
Native range:
Malesia, Kazan-retto, Nansei-shoto,
Ogasawara-shoto
Functional
type:
Filter-feeder
Status in
England:
Non-Native
Status in
Scotland:
Non-Native
Status in
Wales:
Non-Native
Location of
first record:
River Blackwater, Essex
Date of first
record:
1926
Invasion history: Crassostrea gigas, Pacific oyster
Origin
Native to Japan and North-East Asia.
First Record
Pacific oysters were deliberately introduced to GB from Canada during the 1960s for
commercial purposes. The first record from the wild was 1965.
Pathway and Method
Imported into GB from Canada for commercial aquaculture. Natural spatfall now occurs
in several GB sites. Some spat settlement in the southwest of England may have come
from French stock, with possible vectors including transport by current systems,
discarded food waste, transport on ship's hulls and intentional (illegal) introductions.
Species Status
Farmed populations occur throughout England, Scotland, Wales and Ireland, and are
widespread in Europe. It was initially presumed that temperatures in GB waters would
not be suitable for Pacific oysters to successfully spread, settle and spawn in GB
waters, but escapees have established feral populations in south-east and south-west
England and Wales. There are extensive beds of naturally recruited Pacific oysters in
some southern estuaries of England and sparse settlements are known from the north
coast of Wales near Conwy.
Ecology & Habitat: Crassostrea gigas, Pacific oyster
Dispersal Mechanisms
Pacific oyster larvae are planktonic for three to four weeks, during which period they
are dispersed by tidal currents; larvae are documented to travel up to 1000 km on
ocean currents although such distances are unlikely in GB waters. Dispersal of larvae
may allow new populations to colonise areas too cold for successful reproduction.
Reproduction
Pacific oysters change sex during life, most commonly maturing first as males before
subsequently transforming into females. Spawning is temperature dependant and
breeding occurs during summer months at temperatures of around 18 °C. Each
individual may release 50 to 60 million eggs up to a maximum of 100 million eggs
although juvenile mortality is high. Fertilisation takes place externally and larvae are
planktonic for three to four weeks before settling; the lower shell valves are cemented
onto hard substrate.
Known Predators/Herbivores
Pacific oyster larvae are consumed by filter feeding animals. Juveniles are eaten by a
variety of species including worms, snails, starfish, fishes, birds and crabs. Adults are
less vulnerable to predation, but may be preyed upon by birds, starfish and large
crustaceans.
Resistant Stages
None known.
Habitat Occupied in GB
Pacific oysters inhabit intertidal and shallow subtidal estuarine and coastal waters,
settling on hard substrate. Where rocky substrate is scarce the oysters settle on any
available hard substrate including rocks and other shells, and can form dense reefs by
cementing their shells to each other.
Distribution: Crassostrea gigas, Pacific oyster
Native range Japan and Northeast Asia. In GB the Pacific oyster is farmed at several
locations around GB coasts and estuaries. Escapees have established populations in
estuaries in the south-west and south-east of England, and sparse settlements are
known from the north coast of Wales near Conwy.
I m p a c t s : Crassostrea gigas, Pacific oyster
Environmental Impact
In North America the Pacific oyster is known to settle in dense aggregations, excluding
other intertidal species. In the Dutch Wadden Sea and more recently in the GB the
oysters have started to form reefs consisting of dense layers which can alter the
natural state of the ecosystem, posing a potential threat to native species and altering
habitats, some of which are protected under European law. In the Wadden Sea it has
been suggested that these reefs could cause major shifts in benthic filter feeding
populations, which could have detrimental knock-on effects on bird populations.
Health and Social Impact
The sharp oyster shells pose a hazard to humans; the formation of reefs on mudflats
may render the intertidal zone unsuitable for human leisure activities.
Economic Impact
The Pacific oyster is presently the most widely grown bivalve in aquaculture around
the world. In 2006 1400 tonnes were produced in the GB. However, where oysters
establish wild populations economic losses may occur through the loss of mussel and
other bivalve fisheries.
References & Links: Crassostrea gigas, Pacific
oyster
Identification
Miossec, L., Le Deuff, RM., and Goulletquer, P. (2009) Alien species alert: Crassostrea
gigas (Pacific oyster). ICES Cooperative Research Report No. 299.
Biology, ecology, spread, vectors
Child, A.R., Papageorgiou, P., & Beaumont, A.R. (1995) Pacific oysters Crassostrea
gigas (Thunberg) of possible French origin in natural spat in the British Isles. Aquatic
Conservation: Marine and Freshwater Ecosystems, 5 , 173-177.
Minchin, D. & Gollasch, S. (2008) Crassostrea gigas. Delivering Alien Invasive Species
Inventories for Europe. [online] Available from:
http://www.europe-aliens.org/pdf/Crassostrea_gigas.pdf
Management and impact
Couzens, G. (2006) The distribution and abundance of the non-native Pacific oyster,
Crassostrea gigas, in Devon – a result of climate change? Shellfish News, 2 2, 5-7.
Guy, C. & Roberts, D. (2010) Can the spread of non-native oysters (Crassostrea gigas)
at the early stages of population expansion be managed? Marine Pollution Bulletin, 6 0,
(7), 1059-1064.
Maggs, C., Mineur, F., Bishop, J. & McCollin, T. (2010) Non-natives in MCCIP Annual
Report Card 2010-11, MCCIP Science Review, 11pp. Available from:
http://www.mccip.org.uk/arc
Miossec, L., and Goulletquer, P. (2007) The Pacific cupped oyster Crassostrea gigas:
from an introduced species for aquaculture to an invasive species for the ecosystem. In
5th International Conference on Marine Bioinvasions, 21 – 24 May 2007, Cambridge,
MA, Abstract Book. MIT Sea Grant College Program, Cambridge, MA.
Padilla, D.K. (2010) Context-dependant impacts of a non-native ecosystem engineer,
the Pacific oyster Crassostrea gigas. Integrative and Comparative Biology, 5 0, (2),
213-225.
Sewell, J., Lindsley-Leake, S., Tyler-Walters, H. (2010) Non-native species Risk
Assessment for the Pacific oyster Crassostrea gigas. A report to GB Non-Native Species
Secretariat and Defra.
General
Minchin, D. & Gollasch, S. (2008) Crassostrea gigas. Delivering Alien Invasive Species
Inventories for Europe. [online] Available
f r o m :http://www.europe-aliens.org/pdf/Crassostrea_gigas.pdf