Marine census: Surprising number of creatures bipolar

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Enough with the supposed underwater deserts, say polar census workers.

Arctic and Antarctic waters may look scarily hostile for living things. But a preview of a massive count of sea life reports some 13,000 kinds of animals living at one pole or the other, or, in a surprising number of cases, at both.

An international research collaborative called the Census of Marine Life released a glimpse of its findings on February 15, due out in finished form in 2010. Starting in 2000, hundreds of academic and government researchers have been  working to fill in the considerable gaps in information about what has been, is now or will probably be living in the world’s oceans. Including exploration inspired by the International Polar Year, which ends in March 2009, Census scientists have made more than a dozen expeditions to explore life at each pole.

So far Antarctic tallies for the Census have reached some 7,500 animal species, a thousand or two more than were known before, says Julian Gutt of the Alfred Wegener Institute for Polar and Marine Research in Bremerhaven, Germany. He coordinated the science on nerve-testing, round-the-clock research marathons in the Antarctic.

For the Arctic, expeditions have logged around 5,500 kinds of sea animals, including some 235 that appear to be the same as residents at the opposite end of the planet, says Russ Hopcroft of the University of Alaska Fairbanks. He didn’t get much sleep either, as co-leader of more than a dozen research trips into the Arctic.

For the bipolar species, “this number has been much larger than we expected,” Hopcroft says. Some of them, such as gray whales and the seabirds, move around easily, and some, such as one of the little Crustacea called copepods, show up just about anywhere there’s seawater. But others, such as two snail-like species that have become almost as filmy as jellyfish and flutter through seawater instead of crawling, are not known from anywhere in between the poles.

One of these bipolar pteropods, Clione limacina, “looks really cute,” Hopcroft says. But its rounded end hides chainsaw-fierce tentacles that it buzzes into the small shell cavity of another bipolar pteropod, Limacina helicina, for food.

News of so many possible shared species between the poles interests Amélie Scheltema, a systematist studying mollusks. “Genetic work is going to have to be done though,” she cautions, to see whether the populations just look alike but actually function as separate species. (Hopcroft and Gutt agree, and molecular work is on the way.)

Gutt also says he’s looking forward to asking deeper questions about species diversity, such as whether it’s favored or suppressed by the fast-changing vs. the barely changing parts of the polar environments.