The darkest reaches of the ocean have long been thought of as a desolate biome. But as researchers send equipment down to document these mysterious depths, they are quickly learning not only that it is teaming with life, but also that it boasts surprising diversity.

More than 340 scientists from around the world have been working over the past nine years to complete the Census of Marine Life, a project that has sent out dozens of expeditions to document ocean life at all levels of the sea. Final results from the survey will be announced next October, but preliminary results about the deep-sea findings are being released early.

With some 17,650 creatures found living below 200 meters, where photosynthesis stops, (and another 5,722 living below 1,000 meters), the researchers compare the surprising amount of marine diversity with that found in tropical rainforests. Of course, in a rainforest, "it's visually overwhelming," says Robert Carney of Louisiana State University in Baton Rouge and co-leader of the Consortium for Ocean Leadership's Census project, Continental Margin Ecosystems (COMARGE). Even a mere scoop of mud from the ocean floor can contain a wealth of animals that are just millimeters long.

Slide Show: Unusual Deep-Sea Species Documented

Traditional theories of evolution and ecological niches might predict low species diversity in deep, dark marine habitats. Carney notes, however, the sheer number of newly discovered species there "is just counter to what we know about diversity." Some of the reasons for that may include the fact that many of the species are probably very old and their environments have remained stabler than others on the planet, allowing new species to evolve even as they themselves are not driven to extinction.

Beyond the curiosity-driven research that the census has enabled, the researchers also hope the data will be put to more immediate, practical use. "It's the world's largest environment," Carney says of the ocean floor. "We have a very rich system that we really have to deal with."

Even though much of the deep ocean seems out of reach to humanity, it is not entirely untouched by us, notes Odd Aksel Bergstad of the Institute of Marine Research in Norway. The oil industry is now drilling down thousands of meters and even fishing has become more of a deep-sea industry. "The management needs a better scientific basis for making the right decisions," he says.

The impacts of deep-ocean projects might be out of sight, but for researchers working on the census, they are not out of mind. Carney, who has been studying bottom-dwelling life since 1967, says, "It used to be that deep-sea searching was a fairly esoteric area of academia." But now, he notes, scientists in this arena are increasingly responsible for policy recommendations. "Because of the remoteness of the system, if you make a mistake, it's going to be a very difficult mistake to correct," he says. "The greatest threat to the ocean is ignorance of the system."