THEY are the long-lived giants of their species, bottom-dwelling behemoths which can live for forty years or more.
Now scientists are shedding fresh light on the life cycles of the shoe-sized horse mussel, and have uncovered connections between habitats which have never been observed before.
A new report published by Scottish Natural Heritage (SNH) uses state-of-the-art modelling to examine how horse mussel beds around the coasts are linked, as well as examining similar connections between flame shell mussel beds in different locations.
Researchers found that west coast mussel beds could be connected to other beds as far as Orkney and Noss Head, as larvae ride the prevailing ocean currents and create intermediate beds as “stepping-stones” along the way.
READ MORE: Scallop dredging devastates rare flame shell reef in the Highlands
Meanwhile flame shell beds - found mostly on the west-coast of Scotland and in Orkney’s Scapa Flow - were found to be generally weakly connected, making them more vulnerable to any local damage.
A flame shell mussel. Pic: Ben James/SNH
Both species are found in Scotland’s network of Marine Protected Areas (MPAs) and the study modelled the links between populations in both protected and unprotected areas for the first time.
The modelling - a joint initiative between SNH, Marine Scotland Science and Heriot Watt University - suggested that horse mussels and flame shells could reach and form beds in a number of new areas in Scottish waters. Seabed surveys in these areas may confirm the model predictions.
Horse Mussels are similar to the blue mussels found on seashores but grow much larger, and can reach more than 15cm in length and live for over 45 years.
They live individually or in clumps, or may form raised beds with several hundreds of mussels per square metre.
Horse mussels live below the low water mark, with beds found at depths from 5 to 220 metres, although most known beds are between 20-50 metres.
READ MORE: Revealing the secrets of mussels as big as size nine shoes
The beds provide a foundation for soft corals, tubeworms, barnacles, sea firs, sea mats and seaweeds, as well as shelter for brittlestars, crustaceans, worms, molluscs and many other small animals.
Flame shells, bivalve molluscs with a fringe of orange tentacles, live hidden on the seabed in nests which they build from shells, stones and other materials. Hundreds of nests can combine to form a dense bed, which stabilises the seabed and provides substrate for sea firs, sea mats, sea squirts and seaweed, as well as shelter for many other creatures, such as crabs, scallops and brittle stars.
The habitat is found mainly on the west coast of Scotland, often in tidal narrows and the entrances to sea lochs, with the largest known flame shell bed in Loch Carron. There is also a flame shell bed in Scapa Flow on Orkney.
In recent years both have come under threat due to dredging that scours the seabed in the search for fresh mussels.
In July Marine Scotland said it was looking into claims an industrial vessel was last week scraping the bottom of Loch Broom near the Summer Isles.
A diver inspects damage to the mussel beds in Loch Carron. Pic: Chris Rickard
This followed an incident last year where dredging was banned from Loch Carron in Wester Ross following an investigation into claims the beds had been damaged by scallop dredging.
SNH and Marine Scotland are working on a project to improve protection of sensitive habitats - including known horse mussel beds and flame shell beds - outside the MPA network.
The research will help to identify locations where additional protection could improve connectivity between these habitats. The methodology could also be used in future to predict changes in the network due to climate change.
READ MORE: Mussels ‘stressed’ by under sea noise, Scottish research suggests
Flora Kent, SNH Marine Ecology Adviser, said: “Horse mussels and flame shells are two amazing species that greatly increase the richness of our seas. The habitats they form provide vital shelter and structure for a range of other marine species, but they are also sensitive to disturbance.
“The new methods used in this study have, for the first time, given us a really fascinating insight into how different populations are connected all around our coasts, both inside and outside of protected areas.
“By revealing these links, the results help us to understand where additional protection could enhance this connectivity and improve the biodiversity of our seas.”
Alejandro Gallego, Marine Scotland Oceanography Group Leader, added: “This work is a good example of how numerical models of our shelf seas can be applied to understand important ecological processes in the marine environment and provide evidence to develop the marine management policies that enhance the protection of these important and sensitive species”
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