Natural oyster reefs along European coasts have nearly vanished, with only a few small patches remaining due to overfishing, dredging, and pollution.

However, a recent study by British scientists reveals these reefs were once vast, reaching heights comparable to houses and covering an area of 1.7 million hectares (4.2 million acres) from Norway to the Mediterranean—an expanse larger than Northern Ireland.

To reconstruct the historical spread of the European flat oyster (Ostrea edulis), researchers analysed records from the 18th to early 20th centuries, including government documents, fishery reports, nautical charts, and scientific articles.

They uncovered detailed accounts of extensive reefs in 1,196 locations, including the UK, France, Ireland, Denmark, Spain, Germany, and the Netherlands. In one striking report, oyster reefs in the Black Sea reached up to seven meters in height.

Ruth Thurstan from the University of Exeter, co-lead author, expressed amazement at the scale of these reefs.

“I knew that oysters used to be caught in huge quantities, so we suspected that these reefs could be large, but to find information that evidenced such coverage of reefs, amazed me.

“Few people in the UK today will have seen a flat oyster, which is our native species. Oysters still exist in these waters but they’re scattered, and the reefs they built are gone. We tend to think of our seafloor as a flat, muddy expanse, but in the past many locations were a three-dimensional landscape of complex living reefs.”

The reefs once created biodiverse ecosystems that supported nearly 200 species, such as the common stingray, the short-snouted seahorse, and the European sturgeon. They also stabilised shorelines, cycled nutrients, and filtered water.

Thurstan said: “There are a handful of remnant reefs in a few parts of Europe, including the coast of Brittany and the west coasts of Ireland and Scotland. But these are at most a few square metres in extent, as opposed to square kilometres in the past. The significant ecological functions these reefs used to provide no longer exist, which is what we mean by functionally extinct.”

Some historical records reveal the sorrow of those witnessing the reefs’ destruction. One writer in 1852 reported: “In the Wash, about 50 years ago, were enormous oyster beds; one extending nearly the whole length of the Wash and continuing outside about 50 miles.”

A description of a “great” reef three miles off the Isle of Man read: “It took 20 boats seven years to dredge away these oysters. The oysters were thick on that bed … One boat has got 30,000 oysters in a week.”

An account from France describes oyster fishing in 1909: “From 10 April to 24 April, fishing took place. The number of oysters caught was 16 million.”

Though oyster restoration efforts are underway, scientists argue that they need significant expansion to be effective.

Philine zu Ermgassen, an honorary researcher at the University of Edinburgh, noted the reefs’ loss was swift, despite their slow formation. “These were huge areas that were thickly crusted with oysters and crawling with other marine life. There has been a fundamental restructuring and flattening of our sea floors.”

 

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