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Oyster

Oyster ©Paul Naylor

Oyster

Scientific name: Ostrea edulis
Native Oysters are a staple of our seas and our plates - but our love of their taste has lead to a sharp decline all around the UK.

Species information

Statistics

Length: up to 11cm Average Lifespan: 6 years

Conservation status

Classified as a Priority Species under the UK Post-2010 Biodiversity Framework and a Feature of Conservation Importance for which Marine Conservation Zones can be designated.

When to see

January to December

About

Common oysters, also known as Native oysters, live on the seabed in shallow coastal waters and estuaries and will form dense beds where conditions are favourable. Oysters are filter feeders, filtering plankton and detritus from the surrounding water column. They are a type of bivalve (meaning two shells); but their 2 shells are not identical. One shell is rounded and the other is flat, like a lid. Oysters start life as males, but can change sex regularly throughout their lives depending on the temperature of the water. Native Oysters don't produce commercially viable pearls.

How to identify

A large, flattened, clam-like shell. The outside of the oyster is rough, scaly and dark grey with obvious concentric growth lines. The inside of the shell is smooth and pearly white.

Distribution

Unfortunately, years of unsustainable trawling and the spread of a deadly disease has left this once common species in a poor state. Historically it was widely distributed around UK coasts, however, currently, the oyster has a limited distribution with a few strongholds in, the Thames estuary, the Solent, the River Fal and the south-east. It is rare to find an alive native oyster except for near commercial oyster sites.

Habitats

Did you know?

Our native oysters have been an important food source for centuries - the Romans even exported them back to Italy! They are supposedly an aphrodisiac - though there's little scientific evidence to back this up.

How people can help

Native oysters are still harvested in various places around the UK - though it's best to avoid dredged oysters and go for those caught using traditional row and sail boats. Many farmed Pacific oysters are now "triploid" - meaning they are sterile and won't impact on wild populations. It's not entirely failsafe - but they are a more sustainable option. For more information on making good seafood choices, check out Cornwall Wildlife Trust's Cornwall Good Seafood Guide: www.cornwallgoodseafoodguide.org.uk. If you are a diver and encounter native oysters, please let your local Wildlife Trust know.