A single degree of warming in the shallow waters off the Antarctic Peninsula could significantly benefit some species at the expense of others, a new study has found.
In what is claimed to be the "most realistic ocean warming experiment to date" researchers placed heated panels on the sea floor and monitored the growth of sediment-dwelling species on the panels over nine months.
While the panels only warmed the water a few millimetres above the panel surface, it was enough to trigger major changes in the seabed communities, the scientists reported in the journal Current Biology.
"There was one species that really dominated that cover … that really took off with the warming, and managed to cover over the panels," said the study's lead author Gail Ashton, from the British Antarctic Survey and the Smithsonian Environmental Research Center.
"Even just looking at the panels there was a visible difference that's really quite surprising."
The panels were either left at the ambient water temperature, or increased by 1 or 2 degrees Celsius; representing the predicted water temperature increases for the region over the next 50 and 100 years.
A rise of 1C nearly doubled the growth of Fenestrulina rugula; a tiny filter-feeding marine invertebrate.
"You can imagine that one species taking over the whole space and rarer species wouldn't be able to compete with that," Dr Ashton said.
Another species — the marine worm Romanchella perrieri — showed a 70 per cent increase in territory compared to the panels that were kept at ambient temperature.
Results of 2 degree shift less clear-cut
At 2C above ambient water temperature, the winners and losers were less clear-cut, and there was more variation in growth patterns on the panels.
"So have we maybe just pushed some of the individuals within the species to the level where they can't cope; some are able to maintain that increased growth whereas others just aren't able to cope with that change," Dr Ashton said.
The 2C difference with the surrounding water temperature may also have been too much of a shock, in an environment where the water temperature varies by no more than 4C over the year.
"It points to the fact that we need to better understand how organisms from different latitudes are going to respond," she said.
"Some of our temperature curves and predictions in terms of chemical reactions and biological processes just seem to be inherently different at very cold temperatures."
Commenting on the study, marine biologist Jonny Stark from the Australian Antarctic Division said he was surprised at the changes in growth rates even at just 1C above current temperatures.
But he suggested the 1C-2C increase might represent the upper limit that these organisms can cope with.
"On a lot of the Antarctica coast, you might only get less than 1C or 2C of temperature change over a year, so a lot of species have evolved in that context and don't have a lot of resilience or ability to cope with changes outside that range," Dr Stark said.
He pointed out that while this study limited the temperature change to a small increase, other studies suggest higher temperatures have more serious effects.
"It could place a lot of these animals at the upper end of their envelope of tolerance," he said.
"Beyond that, we're not really sure what would happen. You could see some catastrophic differences."