Only a handful of natural oyster reefs of no more than a few square meters cling precariously along European coasts after being obliterated by overfishing, dredging and pollution.
A study led by British scientists has discovered just how extensive they once were, with reefs as high as a house covering at least 1.7m hectares (4.2m acres) from Norway to the Mediterranean Sea, an area greater than Northern Ireland.
The study involved dozens of researchers poring over government records, nautical charts, fishery reports, customs documents, naturalists’ reports, scientific journals and newspapers from the 18th, 19th and early 20th centuries to piece together the distribution of the European flat oyster (Ostrea edulis).
They found vivid – and poignant – stories of often sprawling reefs in 1,196 locations overseas including the UK, France, Ireland, Denmark, Spain, Germany and the The Netherlands. One report from a scientific paper mentioned oyster reefs reaching 7 meters high in the Black Sea.
Ruth Thurstan of the University of Exeter, the co-lead author of the report, said she was “blown away” by the scale of the reefs. “I knew that oysters used to be caught in large quantities, so we suspected that these reefs could be large, but to find information proving 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 are scattered, and the reefs they built are gone. We tend to think of our ocean floor as a flat, muddy expanse, but in the past many places were a three-dimensional landscape of complex living reefs.”
The reefs have created rich ecosystems, providing a habitat for nearly 200 fish and crustacean species, including the common stingray, the short-nosed seahorse and the European sturgeon. They also played an important role in stabilizing shorelines, nutrient cycling and water filtration.
Thurstan said: “There are a handful of remnant reefs in some parts of Europe, including the coast of Brittany and the west coast of Ireland and Scotland. But it is at most a few square meters in extent, as opposed to square kilometers in the past. The significant ecological functions that these reefs once provided no longer exist, which is what we mean by functionally extinct.”
Some of the accounts the researchers found make for sad reading as people realize what is being lost. One writer in 1852 reported: “In the Wash about 50 years ago there were enormous oyster beds; one extending almost the entire length of the Wash and continuing about 50 miles outward.”
A description of a “huge” reef three miles off the Isle of Man reads: “It took 20 boats seven years to dredge these oysters away. The oysters were thick on that bed… One boat has 30,000 oysters in a week.”
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An account of France described oyster fishing in 1909: “From April 10 to April 24 there were catches. The number of oysters caught was 16 million.”
Oyster restoration projects are underway, but the researchers say they need to be scaled up.
Philine zu Ermgassen, an honorary researcher at the University of Edinburgh, said the destruction of the slow-forming reefs was rapid. “These were large areas that had thick crusts of oysters and crawled with other marine life. There has been a fundamental restructuring and flattening of our sea floors.”
The report, The world was our oyster: records reveal the vast historical extent of European oyster reef ecosystemsis available online.
