The results are now being seen as an important resource for assessing the impact of oil in the Gulf of Mexico as well as global climate change, ocean acidification, dredging, and the taking of 100 million tons of marine life every year by voracious humans.
"Imagine if we had no idea of what was there before," said Earle, referring to the Deepwater Horizon spill. "How could we possibly imagine the consequences?"
Ten years ago, Earle said, she and most of her colleagues thought that a census of this magnitude could not be taken.
"This is revolutionary," she said. While most people see marine life as "what's cooked on a plate," she said, "the Census of Marine Life helps us see the oceans with new eyes."
Partial results of the census were published Monday by the Public Library of Science in the public-access journal PLoS One; more results will be released in October. Monday's results included information on 185,000 species as well as patterns of diversity over 25 regions around the world.
A dozen papers explain which species are unique to certain regions, which are found around the globe, and which have invaded new territory thanks to human intervention.
The census project began to take shape in the late 1990s, when the United Nations was attempting to establish a treaty to protect global biodiversity.
To look into the situation in U.S. waters, the National Research Council turned to Grassle, a leader in the discovery of a hidden world of life in the sunless environment of deep-sea hydrothermal vents.
It took some serious perseverance on Grassle's part to get the project started, said marine biologist Ron O'Dor, chief scientist for the census. "He's a calm and hard-to-excite man, but he's very determined and he's also pretty good at finding money."
After two years of trying in vain to find government funding for the census, Grassle got private support from the Sloan Foundation.
Over time the project drew in more than 2,700 people from 80 countries, O'Dor said. Getting the job done required icebreakers in the Arctic and Antarctic, and unmanned submersibles in the deepest midocean trenches, more than six miles below the surface.
Some of the most interesting results came from sonar used to track the populations of fish swimming at various depths, O'Dor said. "That revealed more information about what goes on in the water column than has ever been known before."
O'Dor said he expected a full tally of about 250,000 species to be entered into the database - publicly accessible at www.coml.org - by October.
The rate at which the scientists are still finding new organisms led to the estimate that for every species logged into the database there are four more unknown lurking in the depths.
O'Dor said the census gave scientists a much better "before" picture of the Gulf of Mexico than they had of Prince William Sound before the Exxon Valdez spill in Alaska in 1989. And it will help them evaluate other ongoing environmental threats, from dredging to overfishing, he said.
In a phone interview from his office in New Brunswick, N.J., Grassle said he originally set out to do a complete census of fishes. But so much of the ocean's diversity was made up of other organisms, he said, "it became clear we should be dealing with all the ocean creatures."
The census brought together different areas of study - suddenly shore people were talking to deep-sea people, he said, and marine-mammal people were talking to marine microbiologists.
Grassle said the oceans were changing in alarming ways. Cod and other large fish are dwindling, while smaller species such as jellyfish, less desirable for food, are increasing. The effects of global warming are beginning to appear in the distribution of plants and animals, he said.
Earle, the oceanographer, said that understanding marine life was critical.
"The ocean is the cornerstone of Earth's life support system," she said. "Life in the ocean is vital for generating oxygen, stabilizing the carbon cycle, and otherwise keeping the planet's environment suitable for human life."
It's "stunning" to find how much has changed because of human impact, Earle said, citing a study released last week that suggested a 100-year decline in the world's population of phytoplankton, photosynthetic organisms that make up the base of the marine food chain.
At the current rate, she said, "things are going extinct faster than we can get to know them."
Contact staff writer Faye Flam
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