In the realm of research, finding out what you don't know is almost as important as knowing what you do. In marine biology, however, both of these knowledge bases have been rather murky.

The international Census of Marine Life, a $650 million, 10-year-long endeavor, has started to fill in the large blanks, illuminating new swaths of the mysterious deep along the way. A report on the project's findings was released today at a news conference in London.

Although the combined efforts of the more than 2,700 researchers involved in the study were not quite enough to count every fish in the sea, the scientists have added the names and descriptions of more than a thousand new species to the ever-growing list of known ocean life forms.

The catalogue itself feels like one of the biggest accomplishments to those involved in the work. "We actually have a list of the known named species," says Jesse Ausubel, co-founder of the census project and an environmental scientist at the Alfred P. Sloan Foundation. That might sound basic, but as he points out, when the census started in 2000, those in the field could do little more than guess how many known species there were in the seas.

In addition to the approximately 1,200 species from the census that have been formally described, researchers involved in the work estimate that there are another 5,000 previously unknown species that were collected are still awaiting formal description. But after sifting through new and old lists, members of the research team were able to peg the total number of known marine species at about 250,000—around 20,000 more than typical estimates a decade ago. And many of those species are now searchable in the new Ocean Biogeographic Information System (OBIS) and the extensive World Register of Marine Species (WoRMS), databases with information about at least half of the known species—from killer whales to novel nematodes.

View a slide show of 12 species—some new and others familiar—encountered during the Census of Marine Life

The baseline species counts established by the census have already come in handy. The survey for the Gulf of Mexico region was completed in 2009, listing more than 8,000 forms of life in the region where the oil spill occurred. Current and future studies of the area where the oil rig exploded in April will be able to take into account the recent pre-spill data to help assess the incident's ecological impact.

In 2000, the group was "interested in the known, unknown and unknowable," Ausubel says. To that end, part of the census's mission was to figure out what areas of the world's oceans had not been explored. "The Romans had terra incognita," he says, and now modern marine scientists will have a better idea of which remote regions have yet to be probed. "There are still huge areas to explore, but at least we sort of know what they are," Ausubel says.

Seas of the small
Most of marine biomass belongs to microbes, which comprise as much as 90 percent of total sea life mass, according to the new report. Ann Bucklin, a professor of marine sciences at the University of Connecticut and co-chair of the census's zooplankton project, and her colleagues worked to catalogue what she calls "the hidden diversity."

Whereas many estimates about zooplankton had been based on biomass or functional groups, she has been trying "to put species back in the equation," she says. Armed with a DNA barcode scanner and what she describes as "monster butterfly nets" to capture some of the smallest sea creatures thousands of meters below the surface, their group was able to rapidly sample and document new species and their distributions. "We saw animals alive that no one has ever seen," she says. Pulling up the nets filled with so many rare denizens of the super-deep, she says, was "mesmerizing." She recalls, "We had people jumping up and down saying, 'I've never seen a sample like this.'"

High-throughput DNA sequencing allowed the researchers to get a quick read on genetic material across a large sea sample. But these technological advances are no replacement for traditional taxonomy, Bucklin says. "We still need taxonomists to be able to describe these species and help us understand what's new," she says. However, with only 23 taxonomists on the steering committee in her field—and few students pursuing the work nowadays—she is afraid that "we are losing that expertise…the accumulated knowledge of what's a species."

After cataloging, Bucklin is looking forward to moving beyond the baseline. "We're finding huge numbers of new rare species distributed throughout the ocean," she says, noting that the census data have emphasized that "species are everywhere—and they're rare everywhere." And she wants to know why biodiversity is important. The multitude of species is "beautiful," she says, but "I want to know what they're doing…why in the grand scheme of things" it makes a difference if there are 14 species of plankton in an area rather than seven.

An ocean of data
One of the most difficult aspects of the endeavor, Ausubel says, was keeping all of the teams and researchers focused on the collective goal—and coordinating the flood of data. He compares the experience to "a funny movie from the 1930s where you have a switchboard" and are trying to stay afloat amid a constant rush of new input. His work sometimes came down to a comical roll call, he says, in which he had to ask, "Okay, cephalopod people, what's your number? Sponge people, what's your number? Annelid people, what's your number?" 

In addition to new data coming in from sampling and surveying, he points out, there were also noticeable changes occurring during the decade of the census. The most apparent changes, he says, were in the polar regions, where ice has been retreating. In Antarctica, he notes, "we were there to observe large herds of sea cucumbers moving into areas that had been ice-covered" in previous years.

Climate change, however, is currently only third on the list of the biggest current threats to marine life, Ausubel says. "The number-one threat is direct removal of marine life"—overfishing—he says. The second most severe is destruction of habitat, such as development-driven changes in costal areas and wetlands. But changing climate will be of increasing importance in years to come, and its specific impacts remain unknown. "Climate change will reorganize life in the oceans," Ausubel says, quickly adding, "We don't know how."

Despite many disheartening long-term trends, including coral reef loss and continued overfishing, some success stories have also become evident. "Some of the marine mammals have certainly come back in considerable numbers," Ausubel says. The lesson to be learned, he notes, is that "if we leave areas alone for a reasonable amount of time," many of the species will rebound. However, protected areas rarely recover into an ecosystem that looks like it did before, and instead go through marked "regime changes," he notes.

If anything, the census has opened a proverbial new can of marine worms, leaving scientists anxious to go on with the work.

Many of the researchers are hoping to continue the effort into another decade and will be discussing the plan Thursday in London and again next fall at the World Conference of Marine Biodiversity in Aberdeen, Scotland.

"Are we done?" says Bucklin, reflecting on the marine census. "No. Are we close? No. But boy, did we get a hell of a lot done."