South Tyneside Reef Cubes Help Restore Native Oyster Reefs

Scientists have discovered that purpose-built reef cubes fitted with native oysters can secure new reefs in exposed coastal waters, where previous restoration attempts have failed.

The research changes the outlook for restoring lost oyster reefs in open seas, where rough conditions once dispersed restoration materials before reefs had the chance to establish.

Reef cubes on the seabed

Around 1.8 kilometres off South Tyneside on England’s north-east coast, 20 cubes weighing 6 metric tonnes each now support 4,000 native oysters.

Celine Gamble, project manager at the Zoological Society of London (ZSL), helped design the concrete reef so it could remain stable offshore.

A coarse surface is important because oysters attach more readily to uneven ground, while the openings in every block provide refuge for fish and crustaceans.

The cubes are not a substitute for a complete oyster reef, but they could overcome the initial challenge of establishing one in open water.

Why oyster reefs disappeared

Living oyster reefs have been missing from this coastline for more than a century. Throughout England, native oyster populations declined by roughly 95 per cent after overfishing removed beds faster than the slow-growing shellfish could recover.

Pollution, damaged habitats, disease and dredging then left the remaining oysters isolated, preventing the formation of the dense reefs required for recovery.

By the time scientists began to document the decline closely, the shell ridges that had once raised the seabed had largely been levelled.

What oysters contribute

While feeding through its gills, an adult oyster can filter up to 200 litres of seawater each day. This continuous filtering removes suspended particles, allowing more light to reach the seabed where young marine organisms settle.

As their shells accumulate, oysters create a firm, three-dimensional habitat that gives shrimp, crabs and small fish protection from predators.

Their ability to clean water and create shelter explains why restoration teams focus on rebuilding reefs rather than simply scattering individual oysters across mud.

Oyster reef designed for rough water

Engineers gave each concrete-like cube a mass of about 6 metric tonnes, making it difficult for waves and storm surge to push the structures along the seabed.

Ridges across their outer surfaces imitate natural rock, offering oysters improved attachment points and providing other animals with more places to conceal themselves.

Wide holes through the centres allow water to flow freely while forming small spaces in which fish and lobsters can take shelter.

Since the cubes remain in position once installed, the reef can develop around a fixed structure rather than a shell bed vulnerable to drifting.

Shells, spat and seabed

Alongside the cubes, teams placed spat - juvenile oysters already attached to shells - throughout the site. They also distributed recycled scallop shells as cultch, meaning loose shells that provide baby oysters with a hard surface to attach to.

Oysters cannot create reefs on unstable soft sediment alone, as these tiny creatures need solid ground before they can build up in layers. Additional shells are especially valuable during the early years, when each surviving patch can help form the next layer.

Volunteers helped create the oyster reefs

Before any cube was lowered into the sea, over 90 local volunteers cleaned oysters at North Shields Fish Quay near Newcastle.

Thorough cleaning lowered the risk that unwanted species could be transported to the reef location alongside the oysters.

Almost 100 further volunteers attached oysters to the cubes with glue, making the marine engineering project a community-led restoration effort.

Their work removed a practical constraint, as thousands of oysters needed to be prepared swiftly before the deployment date.

Lessons from 2023

A previous deployment in 2023 placed 10,000 mature oysters off Whitburn, on a nearby section of coast south of the current site.

Severe weather subsequently scattered some of the oysters and shells, demonstrating how rapidly open-coast restoration can break down before the animals become established.

Although the setback did not end the project, it made structural stability the main design priority for the teams.

This year’s cubes directly respond to that experience, and whether they succeed will depend on their ability to endure the first severe season.

Europe’s wider oyster reef decline

Beyond Britain, researchers recently concluded that Europe’s native oyster reef ecosystem had collapsed under an international framework used to assess ecosystem collapse.

Historical evidence indicates that these reefs once covered more than 4.2 million acres, rather than existing as the small remnants seen today.

The disappearance of reef structure was significant because layered shell mounds altered currents, retained marine life and lifted the seabed into productive habitat.

On that scale, the South Tyneside cubes are modest, yet they address the missing structure reefs require to become established.

What success looks like

At first, success may appear unremarkable: the cubes remain in place, the oysters survive, and the shells start to bind together into a single reef.

Fish, sponges and crustaceans should soon begin to arrive as the textured surfaces offer both food and cover.

“They may be small, but oysters can play an important role in keeping our seas clean and healthy,” said Gamble.

Definitive evidence will take time, since a reef can only be considered successful once it withstands storms and begins producing young of its own.

Where this could lead

Off England’s north-east coast, the cubes are examining whether lost reefs can be restored by combining ecology and engineering.

Should the blocks remain secure and the oysters breed, later projects could expand this approach along rough coastlines where loose shells do not work.