Common Oyster

• Every oyster is born male and can change sex several times in its life.
• It broods its larvae for 7 to 10 days inside its own mantle cavity before releasing them.
• Its European populations have been in steep historical decline.
• It is the European flat oyster, the native oyster, and its reefs once covered enormous areas of Europe's coasts. Today they have disappeared from more than 85% of their historical area and are considered one of the most degraded marine habitats in Europe.
• The cause is a combination of historical overfishing, the parasitic disease bonamiosis and competition from the introduced Pacific oyster.
• It is an alternating hermaphrodite and broods its larvae inside the mantle cavity for a few days before releasing them, something the Pacific oyster does not do: it sheds its larvae straight into the water.
• Its reefs were ecosystem engineers: they filtered the water, created three-dimensional structure and harboured a biodiversity comparable to that of a temperate coral reef.
• Today it is the object of major restoration projects in the United Kingdom, the Netherlands, Germany and Spain, with reintroduction of oysters and of shell substrate.
• In the 19th century it was food for the poor in London and Paris, so abundant was it; its status as a luxury is a direct consequence of its collapse.

Skeleton type

Invertebrate - external calcareous bivalve shell (mollusc)

Habitat & environment

Estuaries and shallow coastal waters with hard mud and rock substrates, from Norway to Morocco, the Mediterranean included

Birth weight

A veliger larva brooded inside the mother's mantle cavity before release

Size at birth

A veliger larva released after 7-10 days brooded by the mother, settling 8-26 days later

Sexual maturity

8-10 months (though field studies put full maturity as late as 3-5 years)

Gestation / incubation

7-10 days brooded in the mother's mantle cavity before the larvae are released

Litter / clutch size

Up to 2,000,000 eggs in a large female

Sources consulted: JungleDragon; GBIF; Animalia.bio; Earthpedia; MarLIN; Smithsonian NEMESIS; PMC (genomic prediction growth traits study); Wikipedia (Ostrea edulis)