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Animals without oxygen, underwater

Three species found possibly living where they should not.

12:00am, April 28, 2010

Scientists recently found three animal species living two miles below the surface of the Mediterranean Sea. They’re multicellular, which means their bodies have many cells. They’re also tiny — each about the same size as a large grain of sand — and look like tiny umbrellas with legs. But they are animals.

The most exciting thing about these creatures, say the scientists, is that they apparently don’t need oxygen to live. What biologists know about life so far is that only single-celled organisms can live in places that have no oxygen, and that multicellular organisms can visit these places, but not live there. These newly found creatures could change that idea.

Some species of the animal loriciferan (one shown) may live entirely without oxygen.

Some species of the animal loriciferan (one shown) may live entirely without oxygen.

R. Danovaro

“This discovery is truly exceptional,” Gonzalo Giribet told Science News. Giribet is a biologist at Harvard University and was not part of the discovery.

The three species are types of loriciferan. They live in a part of the world called L’Atalante Basin. The basin is a super-salty “brine lake” that is at the bottom of the Mediterranean Sea and about 120 miles west of the island of Crete. It may seem strange to think of a lake under a sea, but the water in the lake is so salty that it can’t mix with the seawater above it.

Saltwater is denser than freshwater. This means that if you had one cup of saltwater and one cup of freshwater, the saltwater would be heavier. (Try it!) In the basin where the loriciferan live, the water is even saltier than normal seawater — which means it settles onto the ocean floor.

Ordinary seawater has oxygen in it — which allows animals like fish to live — but the super-salty waters of L’Atalante Basin don’t have oxygen. During three research expeditions in 1998, 2005 and 2008, scientists brought up samples from the basin and found the loriciferans. Though small, the critters are classified as animals.

Finding animals down there was so surprising that the scientists couldn’t believe it. At first, “we thought they were cadavers,” Roberto Danovaro told Science News. Danovaro worked on the recent study and is a scientist at the Polytechnic University of Marche in Ancona, Italy.

To find out whether the animals could actually live in the basin — and to be sure the animals weren’t actually cadavers, or the bodies of dead animals, that had floated into the brine from somewhere else — Danovaro and his colleagues brought up more samples from the ocean floor. They placed the samples in small containers filled with nitrogen, which kept out oxygen. Studying the animals in the new samples showed that the loriciferans appeared to be alive.

The researchers did more tests, and found that some of the animals had eggs — which suggests they were reproducing. Also in the samples were old skins, suggesting that the animals had lived there long enough to grow. Finally, pictures taken with a powerful microscope revealed that the insides of the animals appear to be adapted to live in an environment that has no oxygen.

These clues suggest the animals don’t need oxygen, but the evidence is indirect, which means that scientists still have not observed how the animals live without oxygen. This means more studies are needed, but the scientists think they’re on the right track. And if they’re right, biologists will need to rethink what they know about where animals live.

Going Deeper:

Milius, Susan. 2010. “Multicelled animals may live oxygen-free,” Science News, April 9. http://www.sciencenews.org/view/generic/id/58154/title/Multicelled_anima...

Fox, Douglas. 2009. “Invisible fossils of the first animals,” Science News for Kids, February 4. http://sciencenewsforkids.org/articles/20090204/Feature1.asp

Ornes, Stephen. 2008. “Life trapped under a glacier,” Science News for Kids, April 29. http://sciencenewsforkids.org/articles/20090429/Note2.asp

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