What's going on down there? 2,000 ocean scientists do the biggest, wettest census ever

Science News,  Feb 17, 2007  by Susan Milius

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When Hopcroft goes on a cruise, he makes special efforts to collect frail plankton with filmy tissues. Jellyfish may be the most widely known examples, but plenty of other kinds of sea animals, such as salps, have jellylike bodies. To find them, Hopcroft drags an extrafine mesh, extra gently, through the water.

His photographs of a typical catch show translucent shapes shimmering under artificial lights. The creatures range from a few millimeters to a few centimeters in length and may be shaped like barrels, bells, or bananas with wings. Few people have seen even c preserved specimens, Hopcroff says, and even fewer have seen them moving naturally.

The winged-banana group consists of snails that gave up crawling for a life of swimming through open water. The snail foot evolved into various gauzy flaps, some paired like wings. Some of the snails breaststroke through the water, others undulate their panels in birdlike flying motions, and still others row themselves along.

D'Or speculates that marine snails in general "may turn out to be the beetles of the ocean." In species number, beetles far overwhelm other land animals. Census participant Philippe Bouchet of the National Museum of Natural History in Paris sampled coral reefs near three New Caledonian islands. He found several thousand species of microsnails at each site, and as few as 20 percent of the species overlapped between islands.

EVEN SMALLER STUFF For single-celled life, the oceans appear even more diverse. According to genetic analysis of samples from the Atlantic and the Pacific Oceans at various depths, 1 liter of sea water can contain more than 20,000 kinds of bacteria. Mitchell Sogin of the Marine Biological Laboratory at Wood's Hole, Mass., and his colleagues reported this tally in the Aug. 8, 2006 Proceedings of the National Academy of Sciences.

In more news of single-celled organisms, researchers announced last year a new species of what might be know as a giant microbe. It's the newest example of a group of deep-ocean creatures, known as xenophyophores, that live inside gritty particle casings. The casings of specimens of the new species range from shirt-button to coat-button size.

This encased single cell was the discovery of the European project HERMES, which shares personnel with census projects. During a cruise of the Nazare Canyon off the coast of Portugal, the ship had lowered a device that grasps a chunk of the sea bottom. After sampling at a depth of 4,300 m, scientists found flat disks of xenophyophores on the surface of their recovered block of ocean floor.

"They're quite thin, like a crepe,' says Andrew Gooday of the University of Southampton in England. The disks also break easily, so Gooday had to nudge a bit of paper under the casings to remove them from the chunk's surface.

The 50 or so known species of xenophyophores have a wide variety of shapes. They can look like flat plates, tubes, rocklike lumps, and even thin, floppy sheets that Gooday says remind him of "a piece of damp cloth." The largest species form cases some 10 centimeters in diameter. Figuring out the dimensions of the cell inside is tricky, since it threads throughout a network of passageways. Some of the space inside also goes to storage for pellets of the cell's waste.