The lightless depths of the Antarctic’s Southern Ocean harbour an unexpectedly diverse "treasure trove" of marine life, including more than 700 previously unknown species, according to a study released on Wednesday.
A series of expeditions over three years collected samples of fauna living up to six kilometres below the surface of the Weddell Sea, a poorly understood region that supplies much of the deep water circulating in the world’s oceans.
Angelika Brandt, a marine biologist at the Zoological Museum of Hamburg and lead author of the study, said the consortium of international researchers were greatly surprised by what they found.
"We were astonished by the number of new species, and expected to find the same patterns" of low biodiversity reported in the oceans around the North Pole, she told AFP in an interview.
Most of the new life forms discovered were isopods, a vast order of crustaceans ranging in size from microscopic to nearly 30 centimetres long.
Of 674 species catalogued, more than 80 percent had never been previously identified. The expeditions also turned up 160 species of snail-like gastropods and bivalves, along with 76 types of sponges, 17 of them new to science.
"What was once thought to be a featureless abyss is in fact a dynamic, variable and biologically rich environment," said Katrin Linse, one of 21 co-authors of the study, published in the British journal Nature.
"Finding this extraordinary treasure trove of marine life is our first step to understanding the complex relationships between the deep ocean" and the distribution of fauna, she added.
Brandt was especially struck by a tiny amoeboid, epistominella exigua, that seems to thrive at depths below 6000 metres as well as in much shallower waters, showing "a previously unsuspected ability to adapt to a wide range of pressures".
Earlier studies had predicted that the Antarctic depths would be as bereft of marine life as the deep Arctic seas. There are two possible explanations for the dramatic difference between the polar ecosystems, explained Brandt.
One is that the Arctic is very young. "In the Antarctic, marine life has had at least 20 million years available for evolution, whereas the time was much shorter in the Arctic," she said.
The other reason, which does not exclude the first, relates to the Southern Sea’s critical role in the circulation of deep water through the world’s oceans.
The movement of massive quantities of water through the areas investigated "might nourish animals better than in any other deep sea," she said.