Antarctic icebergs
June 17, 2014

Antarctic Species Decline When More Icebergs Are Around

April Flowers for - Your Universe Online

Summer and winter on the Antarctic shore are drastically different. Winters are dark and frozen, while summers are characterized by bright, clear waters, thick with algae and drifting icebergs.

Over the last 20 years of warming, however, the region has experienced massive losses of sea ice in the winter that has allowed icebergs to roam freely for most of the year. A new study from the British Antarctic Survey demonstrates how boulders on the shallow seabed which were once encased in a rich assemblage of species competing fiercely for limited space are now, for the large part, home to a single species.

The findings, published in Current Biology, reveal that climate-linked increase in iceberg activity has left all other species so rare as to be almost irrelevant.

"The Antarctic Peninsula can be considered an early warning system — like a canary in a coal mine," said David Barnes of the British Antarctic Survey in a recent Cell Press statement. "Physical changes there are amongst the most extreme and the biology considered quite sensitive, so it was always likely to be a good place to observe impacts of climate change — but impacts elsewhere are likely to be not too far behind. A lot of the planet depends on the near-shore environment, not least for food; what happens there to make it less stable is important."

Previous research revealed an increased mortality in the pioneer species, Fenstrulina rugula. F. rugula belongs to a group called moss animals, and is a rather unremarkable suspension feeder. Despite frequent diving in the area, a 2013 survey dive showed large areas nearby where no live animals could be found at all. This is the first time such a thing has been reported.

The current research team demonstrates the first assemblage-level changes coincident with increased scouring. They found that not even one species present in 1997 had completely disappeared. Many, however, have become so rare that they play little to no role in the community. By the 2013 survey dive, 96 percent of all interactions involved just one species, F. rugula, resulting in one of the simplest seabed systems found anywhere on the planet. No clear winner or loser could be determined in almost all of the competitive interactions because F. rugula individuals battle against each other.

The team was surprised that such a large effect could be observed so quickly because climate change is supposedly a long-term, evolving process. Barnes says the changes at the Antarctic shores are more than likely just the beginning.

"Warming is likely to increase ice scour mortality and reduce assemblage complexity and could aid establishment of nonindigenous species," the team concluded. "We expect the deeper seabed to become richer in benthic colonization with more ice shelf collapses and fast ice losses, but hard surfaces in the shallows are likely to become deserts dominated by rapidly colonizing pioneers and responsive scavengers—with little role for spatial competition or even predation in shaping the structure of such assemblages."