A Tour of the Unexpected Deep Sea Life on the UK's Tallest Underwater Mountain

While the UK is surrounded by water, its cold seas aren't exactly renowned for interesting flora and fauna. But the first visual survey of an underwater mountain off to the west of Scotland revealed some unexpected species in the less than hospitable waters.

Sure, there are no brightly-coloured tropical fish, but the video above released by researchers at Heriot-Watt University, who took a robot submarine to the Hebrides Terrace Seamount in the Atlantic, shows populations of corals, some of which they'd usually expect to find in shallower depths. You can see the camera pan in excitedly to the muted tones of corals on the reef, with the odd fish here and an appearance by an octopus around the 3:40 mark.

The Hebrides Terrace Seamount climbs to 1400m above the seafloor, which makes it comparatively taller than Ben Nevis, Britain's tallest mountain on land. It's still pretty deep under the surface, though; the team's vehicle went down to 1695m in the mission. And that's why the discovery of the corals was surprising—the environment at that depth isn't particularly accommodating, with a release from Heriot-Watt explaining that the water down there is more corrosive to corals.

In a paper published in the Nature journal Scientific Reports, the researchers reported a total of 109 identified megafaunal taxa, the most commonly observed being the largest known single-cell organism, Syringammina fragilissima. The summit of the underwater mountain was sparse in terms of species numbers, but the flanks were home to a surprisingly vibrant underwater community.

But the happy surprise of the discovery may soon take an unhappy turn. We know that as carbon emissions increase, so does the acidity of the Earth's oceans—and that has the effect of literally dissolving some species. Marine biologist J Murray Roberts, one of the study's authors, told the BBC the same might happen here. "Carbon dioxide release is changing the chemistry of our oceans, and forecasts in the Atlantic are that the corals will be exposed to more acidic seawater and that their skeletons will dissolve away," he said.

So while the corals on the seamount are clinging on for now, their existence—and that of all the other species that depend on them—is only going to get more difficult.

For now, this is precisely what makes them particularly interesting to study, with the researchers explaining they "may provide an important warning gauge of climate change, because they are already growing close to their limits."

"Now we need to get back to these sites to work out how these corals are able to survive in these harsh conditions," Roberts said in a statement.

Meanwhile, there's one piece of good news: at least the site is now recognised as a protected area, having joined the list of Scotland's Marine Protected Areas only less than two weeks ago.