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THE waters around Antarctica may be teeming with a far greater diversity of
larvae than biologists realised. Researchers diving under the ice have
discovered 10 times as many different types of larvae as were previously known
to be there. They could provide a barometer to gauge the effects of climate
change, the scientists say.

Many bottom-dwelling marine animals, such as starfish, have larvae that drift
in the plankton. According to a rule proposed by the Danish marine biologist
Gunnar Thorson in 1950, the diversity of these drifting larvae should decline
from the tropics to the poles as waters get colder. Polar invertebrates are more
likely to produce larvae that stay on the bottom, as food supplies for drifting
larvae disappear in dark polar winters.

However, Damon Stanwell-Smith and his colleagues at the British Antarctic
Survey in Cambridge have found an unprecedented diversity of larval life
drifting in the chilly waters of the Weddell and Scotia Seas, where Thorson’s
rule predicts there should be only a few different species. Their two-year
survey around the South Orkney Islands netted 131 different types of planktonic
larvae in an area where just 12 were known before. “Nobody has sampled all year
round and nobody has looked at larvae in detail,” explains Lloyd Peck, who
supervised the study. “Biodiversity is as high as in temperate and maybe even
tropical latitudes.”

Stanwell-Smith collected the larvae while diving around Signy Island, towing
a plankton net by hand with the help of another diver. The team took samples
every two weeks, even during winter when the sea was covered by ice. They then
grouped the larvae into different types on the basis of their shapes.

In a forthcoming issue of Philosophical Transactions of the Royal Society
B, the team will propose that ideas about the pattern of larval
biodiversity on our planet need to be revised. “All the work taught in
university courses is based on three or four surveys by Thorson in the 1930s and
1940s in the North Atlantic,” says Peck.

A clear picture of larval biodiversity will help biologists assess any
effects resulting from climate change. “If we’re going to see big losses in
species from climate change, the Antarctic is the place to look,” says Peck. “In
an environment where animals are adapted to low, very constant temperatures,
they will be vulnerable to small temperature changes.” Peck believes a slight
but sudden rise in temperature could have a catastrophic effect on the larvae,
as there is probably only a narrow range of temperatures in which they develop
normally.

“Our ideas about polar marine systems are changing very fast,”says David
Barnes, an Antarctic marine biologist at University College of Cork in Ireland.
“There’s a lot more going on in winter than people knew about, probably because
nobody really bothered to look.”