Pacific Oyster

• It was introduced into Europe from the 1970s onwards to replace the European flat oyster, decimated by disease, and has since naturalised and formed wild beds in the North Sea and the Atlantic.
• Its reefs act as ecosystem engineers: they bind the sediment and create shelter for dozens of species, though they displace the native fauna where the oyster is invasive.
• A single individual can filter several litres of water an hour.
• It is the most globalised bivalve in the world: it has been introduced from its original range in East Asia to more than fifty countries, and in at least seventeen it has formed self-sustaining populations.
• In the Wadden Sea it was introduced for aquaculture in the 1980s and escaped almost immediately, colonising the native mussel beds en masse. Today the two live side by side in dense mixed beds without the mussel having disappeared.
• It was thought that north of France the water was too cold for it to reproduce on its own. That was wrong: warming and a greater tolerance than assumed have carried it as far as Sweden and Norway.
• It is an ecosystem engineer: its reefs are complex structures of sharp-edged individuals cemented together, which damp down wave action and create habitat.
• Its scientific name is disputed: many authors now place it in the genus Magallana.

Skeleton type

Invertebrate - external calcareous bivalve shell (mollusc)

Habitat and environment

Hard intertidal and shallow substrates of estuaries and bays

Sexual maturity

Under 1 year

Litter / clutch size

Between 50 and 100 million eggs per female and spawning

Sources consulted: Thunberg (1793); Ruesink et al. (2005); Reise et al. (2017); ICES Journal of Marine Science (2021); ScienceDirect (Hughes 1989); Science Advances, How colonial animals evolve; Wikipedia, Zooid