A diving expedition is under way to uncover the secrets of giant horse mussels on Scotland's seabed.

Researchers from Edinburgh's Heriot-Watt University have headed to Scapa Flow, Orkney, to examine the habitat of the mussels, which can grow to almost 10in-long, equivalent to a size nine shoe, and can live for up to 50 years.

The team hopes to conduct 100 dives over the next two weeks.

William Sanderson, from the university's school of life sciences, said: "Due to their longevity, they're not really edible. They are rumoured to be quite tough and probably have quite a lot of muck in them, but their age is also a fantastic way for us to discover clues about the environmental quality of their habitat and what we can do to protect these cold water reefs from damage."

It is hoped that information gathered on the expedition will help scientists develop ways to monitor the environmental quality of the mussel beds. They will look at ways to restore damaged beds and examine how the creatures give shelter and nutrition to other sea life.