Researchers with the British Antarctic Survey looked at a 500-square-metre patch of sea floor in 1997, and found the boulders were crusted with a colourful, diverse patchwork of creatures called "moss animals," a group of invertebrates that live like corals, but are not closely related them. Like corals, they are filter-feeding animals that live in colonies, and can have hard or soft bodies.
But when researchers returned in 2013, only a single species – a fast-growing moss animal called Fenestrulina rugula that Barnes describes as "a classic weed" — was visible on most rocks, they reported in the journal Current Biology this week. Other species had become extremely rare.
"The structure of biodiversity has fundamentally changed," said David Barnes, lead author of the study. "Although the same species are still there, most of them are now so vanishingly rare, that they effectively play no part in the system."
The culprit? Icebergs.
As the glaciers retreat and the ice shelves collapse on the West Antarctic Peninsula, they break off into floating chunks of ice, some of them extremely massive.
Fifty years ago, icebergs couldn't move around much because most years, the sea surface was frozen for much of the year. But recently, Barnes said, most years, the sea is frozen for less than 50 days a year. That leaves the icebergs free to drift and blow in the wind until they crash boulders on the sea floor, pounding and scraping away everything that lived on them.
"It's catastrophic, really," Barnes said. "They kill 99 per cent of things they come in contact with."
Because most of an iceberg is underwater and some icebergs are massive, they can cause destruction as deep as 600 metres below the surface, Barnes added. That means the area of the sea floor that icebergs are stripping of its biodiversity could be vast.
Barnes is concerned because high biodiversity helps protect ecosystems against disturbances such as invasive species.
The low biodiversity left behind by the icebergs mean "the system could now be very fragile and fall over," he said.
When asked if he thought something similar could happen in the Arctic, Barnes said, "Absolutely."
He suggested that similar, sudden losses of biodiversity could be happening along other coastlines around the world as a result of other effects of climate change.
Barnes's team is now collaborating with other researchers to see whether icebergs are destroying biodiversity on the sea floor in other parts of the Antarctic.