Hopp til hovedteksten
The Pacific oyster
Print friendly version

The Pacific oyster

The Pacific oyster is easily differentiated from the indigenous European flat oyster by its shape and shell structure. The European flat oyster has a rounded flat shell with a fine, “flaky” surface. The Pacific oyster is usually longer, has a cupped lower shell and a rough surface, often with radial brownish or violet lines.

The Pacific oyster originates from South-East Asia. It has been introduced to many areas outside its native range as an aquaculture animal. The Pacific oyster is robust and adaptive and has established self sustaining populations in several areas where it has been introduced. It settles mainly in the littoral zone and tolerates periods out of the water at low tide. Dense populations can form oyster banks or reefs, changing the ecosystems. Such dense populations have become established in the Netherlands, Germany and the Danish Wadden Sea. The Pacific oyster is considered invasive, and further spread is not desired.

The Pacific oyster in Norway

The pacific oyster is spreading in Scandinavia. Scientists in Norway, Sweden and Denmark are collaborating to describe the spreading and the effects on the environment. It has been present in Denmark for some time. Since 2006, Pacific oysters have been found at numerous coastal sites along the Swedish west coast, the south coast of Norway and at some sites north to Hordaland County. The Institute of Marine Research needs information from the public, in order to map the distribution, density of populations and the dynamic of the spreading.

Pacific and flat oysters

Pacific (left) and flat (right) oysters

Facts about The Pacific oyster

Latin / scientific nameCrassostrea gigas
Family: Ostreidae
Life span: More than 20 years, more than 25 cm shell height and maximum weight more than 1,5 kilos
Habitat: attached to hard substrate, usually on rocks, gravel or mussel shells from the littoral zone, down to a few meters depth
Spawning: during summer, dependent on warm water. Fertilization in the water, larvae are planktonic for several weeks until they settle. 
Food: Filter phytoplankton, bacteria, other microbes and detritus from the water