Horse mussels need more protection in UK waters, scientists warn

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A species of snail that can reach the length of a British shoe size may be at risk due to unprotected areas of sea near its bed, according to a new study.

Horse mussels, some of which are around 20cm long, can live for decades and are found around the British Isles, with most being seen in the North.

Marine experts have described their beds as “biodiversity hotspots”, providing foundations for soft corals and barnacles, shelter for many small sea creatures and habitat for seashells.

They have been known to be in decline since the 1990s and Marine Protected Areas (MPAs) have been introduced to protect their numbers.

But a new study by scientists at Heriot-Watt University shows the species is at risk due to a “failure” to account for gaps between the protected areas of the sea where their beds are located.

Dr Jo Porter, based at the Orkney campus of Heriot-Watt, worked on the research with Dr Clara Mackenzie from Fisheries and Oceans Canada, scientists and nature managers, to sample schools of horse mussels around Scotland and analyze their DNA.

Horse mussels, some of which are around 20cm long, can live for decades and can be found around the British Isles (Heriot-Watt/PA)

She said: ‘We wanted to know if these areas are actually doing their job of protecting horse mussels and how they network together.

“This is particularly important because, like many protected marine species, the larvae spend time traveling through plankton before settling.

“What we have found is that spaces and connections between MPAs are essential for mussel beds.

“Some of the horse mussel beds could not survive without the network, they depend on the unprotected spaces in between.”

The team analyzed the genetic markers of certain mussel DNAs, assessing how genetically connected and diverse the populations were: low genetic connectivity and diversity could make them less resilient to environmental change.

Divers have gone to depths of over 40m to take samples from some of Scotland’s 12 MPAs where horse mussels are found.

Their research showed that the horse mussel bed at Noss Head, which covers 385 hectares and is one of the largest horse mussel beds in the UK, could be at risk if other beds of the species are not properly protected.

Indeed, their genetic sampling suggested that the bed depends on larvae from as far away as Shetland.

Dr Porter said the findings argue for more research into how MPAs work.

“Marine protected areas are a great tool to protect marine species, but we know next to nothing about how they are connected, despite many governments engaging in so-called networks,” she said. .

“Horse mussels are just the tip of the iceberg – there are many other species of huge conservation and biodiversity importance that are protected by marine protected areas.

“But, as with horse mussels, they could be much more vulnerable than we think, despite being in protected areas.”

Dr Mackenzie added: “Our findings suggest that horse mussel beds in Scotland are an interconnected system of populations.

“It is imperative that conservation decisions consider the complexity of these relationships, rather than simply protecting representative sites.”

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