A PIONEERING experiment is testing whether one of the North Sea’s most important ecosystem-building shellfish can be brought back to the seabed of Dogger Bank
The first 15,000 horse mussels have been placed on the sea floor in what could become an important step towards restoring one of the North Sea’s lost habitats.
The mussels have been deployed at four locations as part of an experimental restoration project led by the Doggerland Foundation and supported by the Endangered Landscapes & Seascapes Programme.
During a recent expedition involving the Doggerland Foundation, ARK Rewilding Netherlands, Blue Marine Foundation and Atlantic Technological University, the team tested several different ways of establishing the mussels on the seabed.
The trial sites will be monitored over the coming years to discover whether the mussels survive, reproduce and, eventually, begin building new reefs. If they do, the results could help inform much larger-scale restoration across the Dogger Bank.
Covering approximately 2.5 million hectares across UK, Dutch, German and Danish waters, its shallow seas are among the most productive areas of the North Sea.
They provide spawning, nursery and feeding grounds for fish, seabirds and marine mammals. But the seabed has undergone centuries of pressure, particularly from bottom trawling, which has severely degraded habitats including the shellfish reefs that once formed an important part of the ecosystem.
Horse mussels are native to Dogger and, given suitable conditions, can form extensive reefs. Once large numbers establish themselves, their shells create a complex three-dimensional structure on the seabed.
Those structures provide crevices and sheltered spaces in which other marine organisms can live, feed, reproduce and take refuge.
Roos Bol of ARK Rewilding Netherlands describes the horse mussel as “a true ecosystem builder”.
“Under the right conditions, they build new reefs shell upon shell, containing all kinds of crevices, nooks and crannies – perfect for various animal species to live in, shelter, lay eggs on and feed,” she said.
The mussels also filter particles from the water and can help stabilise sediment around the reefs.
The 15,000 mussels have been placed using three different methods. Some have been put into steel cages, others into cotton bags, while some have simply been released loose onto the seabed.
The four trial sites will allow researchers to compare the different approaches and determine which gives the mussels the greatest chance of becoming established.
Can the reefs of Dogger Bank return?
There is already experience of restoring oyster reefs, but applying similar principles to horse mussels in the open North Sea presents a very different challenge.
Emilie Reuchlin, Director of the Doggerland Foundation, said the project has been building its understanding of the restoration possibilities for several years.
“With the release of 15,000 horse mussels, we can observe what these shellfish actually need to form reefs,” she said.
“This experiment is a first step towards scaling up in the coming years.”
The project team plans to return to the trial sites in spring to assess how the mussels have established themselves.
Monitoring will then continue for several years. Researchers will be looking for evidence that the mussels have survived, reproduced and begun creating the structures that could eventually develop into functioning reefs. That evidence will determine whether restoration can be expanded across the Dogger Bank.
Reuchlin says the potential prize is considerable.
“We have experience with oyster reef restoration, but for the first time in the North Sea, we are going to attempt to restore horse mussel reefs,” she added.
“If these horse mussels can survive and reproduce here, the future prospect of a healthy Dogger Bank with a rich and vibrant seabed comes back into view after centuries of decline.”
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