Horse mussel beds are listed as priority marine habitats, and are a Priority Marine Feature in Scottish waters.
The horse mussel is a large mussel growing to 22 cm (9ins).
In Scottish Gaelic, the species is called ‘clabaidh-dubha’ (‘clabby doos’), meaning ‘big black mouths’.
It is found growing on hard substrates including shells and stones. By the time they reach about 4 cm long, at an age of 4 years, individuals are too large and tough to be predated upon by starfish, whelk and crabs.
Horse mussels can form dense raised beds down to around 100m depth, providing refuge for a wide variety of species. This is just one of several ecosystem services that horse mussel beds provide, including water filtration and locking up carbon.
The mussels are extremely long-lived (up to 50 years) and are therefore very slow to recover from damage or disturbance.