Horse mussels (Modiolus modiolus) can be primarily found in the North around the British Isles. The species is able to live for several decades and its beds are known to provide an important foundation for barnacles, tube worms and soft corals, while sheltering small sea creatures and shellfish such as scallops.
Horse mussels tend to live between depths of five and 280m where they attach to rocks or partly bury themselves in sediments. While they can live singly or in small clumps, they most often form large beds and reefs.
In the 1990s, MPAs were introduced to counteract the declining numbers of the species. However, a new study has found that the species is still at risk due to a widespread failure to protect the gaps between the MPAs where their beds lie.
The study which was published in the journal Frontier in Marine Sciences saw a team of scientists from Heriot-Watt University and Fisheries and Oceans Canada sample horse mussel beds around Scotland to analyse their DNA to find out how genetically connected the populations are.
“We wanted to find out whether these areas are actually doing their job of protecting the horse mussels and how they operate as a network,” said Dr Jo Porter who worked on the study.
She added: “This is especially important because, like many protected marine species, the larvae spend time travelling in the plankton before they settle. What we discovered is that the spaces and connections between MPAs are essential for the mussel beds. Some of the horse mussel beds wouldn’t be able to survive without the network, they are dependent on the unprotected spaces in between.”
After analysing the samples, the team of scientists established that one of the UK’s largest horse mussel beds, the Noss Head horse mussel bed which covers 385 hectares, relies on larvae coming from as far as Shetland, suggesting that the different beds are more connected than previously thought.
Dr Porter said: “Marine protected areas are an excellent tool for protecting marine species, but we know hardly anything about how they are connected, despite many governments committing to so-called networks. Horse mussels are just the tip of the iceberg – there are many other species that are hugely important for conservation and biodiversity that are protected by marine protected areas. But, as with horse mussels, they could be far more vulnerable than we think, despite occurring in protected areas.”
As Scotland’s horse mussel beds seem to be an interconnected population system, the new research shows that more research needs to be done to find out how MPAs function exactly.
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Photography courtesy of Heriot-Watt/PA & Pexels.