Pictured: European flat oysters (Ostrea edulis). "Our findings present a sobering reminder of the scale of work to be achieved if we are to restore even a small fraction of what has been lost from our seas," say researchers.
Photo: Stephane Pouvreau / Ifremer / University of Exeter.
Once thriving along the shores of Europe, oyster reefs have largely vanished, according to new research published in the scientific journal Nature Sustainability. The study, led by the University of Exeter and the University of Edinburgh, highlights the extent of these lost ecosystems, which once spanned over 1.7 million hectares (4.2m acres) – an area larger than Northern Ireland – stretching from Norway to the Mediterranean.
Based on historical documents from the 18th and 19th centuries, researchers uncovered that European flat oysters (Ostrea edulis) formed massive reefs, creating complex habitats teeming with biodiversity. These oyster reefs supported nearly 200 species of fish and crustaceans, played a vital role in stabilizing shorelines, and filtered up to 200 liters of water per adult oyster each day.
The study, involving over 30 European researchers from the Native Oyster Restoration Alliance, provides the first quantitative description of Europe’s historical oyster reefs.
“Oyster reefs were once a three-dimensional, thriving landscape on the seafloor,” said Dr. Ruth Thurstan of the University of Exeter, in a news release. “Human activities have affected the ocean for centuries. This makes it difficult to discover what our marine ecosystems used to look like, which in turn hampers conservation and recovery."
“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 – now completely lost from our collective memory," added Thurstan, who also forms part of the Convex Seascape Survey, an ambitious five-year project investigating ocean carbon storage.
Oysters, once economically and culturally significant across Europe, were extensively documented in historical records. From nautical charts to interviews with fishermen, researchers pieced together descriptions of vast oyster reefs, with the largest concentration found in the North Sea, along the coasts of countries like France, Denmark, Germany, the Netherlands, Ireland, and the UK.
Dr. Philine zu Ermgassen from the University of Edinburgh noted that the reefs were slow to develop, as oysters built up on the shells of previous generations, but their destruction through overfishing was rapid.
“This has caused a fundamental restructuring and ‘flattening’ of our seafloors – removing thriving ecosystems and leaving an expanse of soft sediment behind," Ermgassen explained.
“Thanks to this historical ecology research, we are now able to quantitatively describe what oyster reefs looked like before they were impacted, and the spatial extent of the ecosystems they formed. These were huge areas that were thickly crusted with oysters and crawling with other marine life.”
While isolated oysters still exist, the expansive reefs that supported rich marine life are mostly gone. However, ocean restoration projects across Europe, such as The Wild Oysters Project in the UK, offer hope, the researchers suggest.
While these initiatives are key to restoring oyster habitats, the researchers emphasize that large-scale restoration efforts, supported by governments and policymakers, are essential for meaningful progress.
In the full scientific article, the researchers note that this data is important for informing policy on ocean restoration, instead of basing targets on "remnant populations": "Our findings demonstrate that restoring even a fraction of these past habitats requires both ambitious policy agreements and a step-change in our understanding of the long-term nature of human-induced ecosystem degradation and the scales of historical loss in marine ecosystems," the researchers argue.
"In addition to informing restoration targets, our findings present a sobering reminder of the scale of work to be achieved if we are to restore even a small fraction of what has been lost from our seas," they conclude.
Source: "Records reveal the vast historical extent of European oyster reef ecosystems" by Thurstan et al., Nature Sustainability (2024).