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Mediterranean invasive species factsheet

MOLLUSCS

Reproduction Common name: Pacific oyster

Radial folds No teeth
identification

Scientific Name:
Crassostrea gigas
Picture

Key identifying features
Brief history
The Pacific oyster shell is extremely rough and
irregular and usually elongated, although its shape
can be variable. Adults can be larger than 40 cm but
the usual size is 10–15 cm. The two valves are
unequal in size and shape, with large, irregular,
rounded radial folds. The upper flat valve is smaller
than the lower cup-shaped valve. It is typically whitish
grey with veins of purple and greenish brown. The
shell interior is pure white with a smooth, shiny summer. Fertilization is external and the larval cycle
surface. ranges from 3 to 4 weeks. Oyster spat that has settled
on hard substrate becomes reproductive after a year.

Field identification signs and habitat
This species occurs on rocky and muddy bottoms
from the intertidal zone down to a depth of about 15
m in shallow, sheltered bays. It can be found in
estuaries and coastal sites as it tolerates a wide
range of water temperatures (4–35 °C) and salinities
(10–40 psu).

Reproduction
Pacific oysters can be hermaphrodites or change sex
during their lives. Spawning depends on water
temperature and generally occurs at around 18 °C in
Crassostrea gigas. Photo: L. Schroeder - www.PNWSC.org

Crassostrea gigas. Photo: B. Weitzmann Crassostrea gigas. Photo: A.M. Arias

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