Divers unveil hidden life of Fair Isle's sea caves

Divers have documented the hidden habitats of the sea caves of a remote island for the first time in a project to increase understanding about them.

Marine surveys were carried out in about 70 caves on Fair Isle, with dive teams battling difficult weather conditions to carry out full biological surveys of four.

Images captured beneath the waves show the characteristic sea cave habitats and the species discovered, including the beadlet anemone, corals, sponges and the baked bean sea squirt.

Fair Isle, situated between Shetland and Orkney, is home to Scotland’s only Demonstration and Research Marine Protected Area (MPA), designated in 2016.

A starfish was found hanging on a mat of colonial baked bean sea squirts. PA Media

The data gathered will help to map the sea caves around Fair Isle in more detail and increase knowledge about habitats and species in the community-led MPA, as well as sea caves around Scotland’s coastline more widely.

The surveys were commissioned by NatureScot and carried out this summer by a team of divers from Heriot-Watt University.

Carol Hume, NatureScot marine protected areas adviser, said: “With so many challenges facing a survey of this kind – not least the weather and remoteness of this special Scottish island – we were really delighted to reach Fair Isle and complete work with the survey team.

“To have gathered information for around 70 sea caves is a fantastic achievement and, along with four biological surveys, has given us a much greater understanding of these hidden habitats within the MPA.

“While the sea caves have been explored by local residents and divers, this is the first extensive and systematic documentation.

“It was an extremely special survey to be part of and we were hugely welcomed by the local community, for which we’re really grateful.”

The caves surveyed included one on the west of the island known as Diamond Cave which is 200 metres long.

Dr Dan Harries, a marine ecologist at Heriot-Watt University, said: “The coastline of Fair Isle is breathtakingly spectacular and it was a privilege to document the sea caves and their inhabitants.

“The majority of the sea caves were very shallow, so their walls were heavily scoured: the sand and stones on the bottom swirl around the cave during heavy seas, scrubbing off any life that might cling to the walls.

A squat lobster was found beside a closed beadlet anemone. PA Media

“The caves with deeper floors are where richer communities had established themselves. Some cave walls were decorated with the sponges including the delicate ‘lace sponge’, others with dense thickets of oaten pipe hydroids, which are related to jellyfish and corals.

“The deeper caves were also home to the aptly-named baked bean sea squirt, which looks exactly as you might imagine.”

The Fair Isle Demonstration and Research MPA is a community-led designation, with the aim of supporting research to expand understanding of the local marine environment, implement impactful conservation measures and illustrate the influence of small communities on policy development.

Stewart Thomson, a member of the Fair Isle community, said: “As a participant in the Fair Isle Marine Environment and Tourism Initiative (FIMETI), and a one-time scuba diver, I was very interested in the cave survey team’s visit in August.

“I was pleased that the island was given a talk demonstrating what they were finding and explaining how and why the various organisms and animals choose to live in such seemingly challenging habitats; and stressing their importance in the wellbeing of marine life.”