Hot spots in a frigid ocean

Climate change will dramatically alter life in the oceans, scientists say, but there is so much still to learn about marine ecosystems that it is hard to know exactly how. Recently, researchers with the British Antarctic Survey offered a glimpse of that future with the results of an unusual study years in the making. The study was published in the journal Current Biology.

The cold, dry ecosystems on Antarctica itself cannot support anything bigger than an insect. But the Antarctic Ocean swirling around the continent paradoxically teems with life. Climate change is a big concern here, because heat-trapping gases such as carbon dioxide are having their biggest effects near the poles. Computer models predict that in 50 years the Antarctic Ocean will warm by about 1.8°F, and by 3.6°F within a century. “We’re going to start to see changes there first,” said Gail V Ashton, an author of the study and a marine ecologist now at the Smithsonian Environmental Research Centre, USA. Trying to predict those changes, scientists have been gathering various sorts of clues. Some look at the natural ranges of Antarctic species, observing the highest temperatures they tolerate. Others put animals into laboratory tanks and manipulate the aquatic environment.

In recent years, scientists like Rebecca have attempted another kind of experiment: heating the ocean itself. The research typically involves putting heated panels underwater, close to shore, and then observing how the temperature increases affect the growth of tiny animals on the sea-floor. Each panel warmed the water, but just a layer eight-hundredths of an inch deep. One set of panels had enough power to increase the temperature by 1.8°F; another set heated the water by 3.6°F. For control purposes, a third set of panels was left unheated. Gail donned scuba gear and dove periodically to track the progress of the experiment. At the end of the experiment, Gail and her team hoisted the panels from the sea-floor. Back at the station, she inspected the marine life under a microscope.

When the experiment began, Gail had been sceptical that she would see much change. Some of her more optimistic colleagues had pointed out that biochemical reactions can occur faster at higher temperatures. They thought animals on the warm panels might grow 10% faster. It did not take many dives for Gail to realise the animals were growing even faster. One species of worm grew 70% faster on a panel heated by 1.8°F, compared with its growth on unheated panels.

The results on the panels heating water by 3.6 °F were even more puzzling. On some, animals grew more; on others, less. Even within each species, Gail and her colleagues found that individuals varied a lot in how well they fared.