The waters of Noss Head, just north of Wick in Caithness are designated as a Marine Protected Area for the largest horse mussel bed in Scotland, which lies at sea depths of 35 to 45 metres.

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Horse mussels are similar to the blue mussels of shallow waters and rocky shore, but are much larger – from 10-20 cm long – with a very thick blue-black shell that has a glossy brown covering. They are long-lived, many survive for more than 25 years and some may be over 50 years old. The young mussels are eaten by crabs and starfish, but once the mussels grow to more than 6 cm long, they are relatively safe from predators. The horse mussel beds become home to many other animals, including soft corals, tubeworms, barnacles, sea firs, and sea mats. Brittlestars, crabs, worms, molluscs and many other small animals find shelter in the nooks and crannies of the shells.