European oyster reefs that once grew to the size of football pitches and collectively covered an area of over 1.7 million hectares – larger than Greater London – have been reduced in modern history to mere shadows of their former glory; the thriving ecosystems they once provided “lost to living memory,” according to researchers from the Zoological Society London.

In fact, so damaged have these reefs, native to Europe, become by human impacts that they are now considered ‘collapsed’ ecosystems on the scale of measurement used by the IUCN Red List Ecosystem criteria.

These once thriving marine environments, historically considered to be the European continent’s equivalent to a tropical coral reef with a diverse, abundant, and flourishing community of fish, crabs, starfish, and birds – such as the distinctive oystercatcher – were vital habitats for many species while providing food for people, stabilising shorelines, cycling nutrients, and filtering water.

Nowadays – and in comparisons drawn via newly compiled historical data providing an image of oyster reefs of the past – they present a far sorrier state. In fact, current definitions of the oyster reef habitat specify simply a ‘handful of oysters on the seafloor’ as their defining feature.

Due, primarily, to overexploitation compounded by poor water quality and disease, the seafloor now presents a flat, barren expanse of sediment with low diversity. European oyster reefs are now so scattered and degraded that – with the exception of a few locations in Norway and Sweden – they are largely found in isolation or in tiny clumps.

“The ecosystem has been lost from living memory and the benefits it provided have only just been realised now it’s almost too late,” said Alison Debney, Zoological Society London conservation lead, wetland ecosystem restoration, and co-founder of the Native Oyster Network UK & Ireland.

“The stark contrast between the modern day flat seabed and historical data must act as a wake-up call for action to restore the once-thriving marine environments.”

In Europe, most oyster populations exist in densities of less than one individual per square metre. Where they are found grouped together, these oyster clumps cover less than 0.1 hectare.

While efforts in recent years have been made to restore the health of European oysters beds, a lack of “ecologically meaningful data” and an “accurate definition” of what a thriving oyster reef would have once looked like has, until now, hampered advances somewhat. 

“Piecing the historical data together with data from current restoration and recovery efforts, we were able to define the original structure and function of the native oyster reef ecosystem. We were shocked by our findings,” said Dr Philine zu Ermgassen of the University of Edinburgh.

“We knew from other regions that oyster reefs were important and we have long known that they are highly degraded in Europe but pulling all this information together in a structured way, as required by the IUCN Ecosystem Red Listing Framework, brought to light the critical role that oyster reefs once served.”

But while the IUCN ecosystem red listing delivers bad news, specialists from across Zoological Society London (ZSL), as well as a number of specialist universities maintain that it is not yet too late to reverse these fortunes and bring oyster reefs back to their historical vibrancy.

It’s believed that reviving the oyster ecosystem would trigger a “cascade of recovery” for other species, too – present a beacon of hope in the face of ecosystem collapse. But, this won’t be a quick turnaround as oyster reefs are notoriously slow to generate, with layers of new oysters building up on the dead shells of their predecessors.

“This IUCN Red List of Ecosystems assessment of Europe’s native oyster reefs has revealed the true scale of what we have lost. But it also points to solutions,” said Marcos Valderrábano, programme manager Red List of Ecosystems, IUCN.

“This assessment serves as a wake-up call to protect and restore ecosystems that are not only vital to biodiversity but also provide invaluable services to people and the planet.”

The motivation to do so ought to be high. Restoration of native oyster reefs and other coastal habitats can have multiple benefits, including boosting local economies through job creation, increasing the security of coastal livelihoods by improving fish and shellfish stocks, and boosting the tourism and recreation industries.

There are currently 18 native oyster restoration projects underway across the UK and Ireland, all of which are members of the Native Oyster Network UK & Ireland, which works closely with the Native Oyster Restoration Alliance – a sister network – supporting efforts across Europe. Meanwhile, partnership projects such as The Wild Oyster Project through which ZSL is working with local efforts and coastal communities in North Wales and Northeast England, play a vital role in local restoration. 

But local efforts like these need the support of larger infrastructure that takes innovative approaches to restoring oyster reef ecosystems if the scale of restoration required is to be reached. To this end, the Nature Restoration Law – part of the EU Biodiversity strategy for 2030 – commenced on 18th August, 2024 with a binding target to restore 30% of degraded ecosystems, particularly those with the most potential to capture and store carbon and prevent and reduce the impact of natural disasters.

“To restore or create more than 500,000 hectares of a range of wildlife-rich habitats outside of protected sites by 2042. This is a call to countries to urgently prioritise and make sufficient resources available to restore this ecosystem at an ecologically meaningful scale,” said Ermgassen.

“Current recovery efforts will be insufficient. We need to look back in time to work out a true but ambitious baseline for what healthy oyster reef ecosystems looked like to restore them to their vital ecosystem services potential – not base it on modern understanding, which has felt the impact of added pressures like over-fishing and other human impacts.

“While UK and EU Restoration efforts are a commendable starting point, a cross-sector approach is needed to halt destructive activities. Small-scale restoration projects are valuable, but true ecosystem recovery requires systemic processes and sustainable financing.”

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