Massive Count a Drop in the Bucket

Decade-long Census of Marine Life leaves plenty to discover.

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By Susan Milius, Science News

A 10-year international project called the Census of Marine Life has come to an end with what has to be one of the strangest census reports ever.

At the project’s finale in London October 4, a summary of the collaboration by 2,700 scientists from more than 600 institutions around the world highlighted their own undercounts and the vast realms they missed. That, however, was the point.

“There’s a lot of ocean left to explore,” says environmental scientist Jesse Ausubel, a census cofounder and program officer of the Alfred P. Sloan Foundation. The water world covers the majority of the planet, feeds people far inland, offers exotic compounds for drugs and manufacturing, regulates the planet’s climate and provides half its oxygen, but has yet to be fully explored.

How many fish in the sea? The census didn’t try to count, since scientists haven’t even finished naming species of marine fish. According to the census summary, the tally of 16,764 marine fish species formally named as of early 2010 probably falls short by an estimated 5,000 species.

And fish aren’t the half of it. They’re perhaps 12 percent of the total of marine species, according to the census estimates. Fishes trail after crustaceans and mollusks in number of species, and researchers report evidence of major undercounts in the numbers of recorded species for these other groups too.

Overall at least 750,000 marine species, not including microbes, still await discovery, the census teams predict. In the seas, the mysteries easily outnumber known species, now estimated at 250,000.

For microbes, the census researchers report boggling diversity. Analyzing a liter of seawater revealed 38,000 kinds of microbes, and census DNA sequencing has turned up specimens of more than 100 phyla. Such breadth approaches three times the number of phyla known in the animal kingdom. Estimates for the total number of kinds of marine microbes run as high as a billion.

Undersampling afflicts oceans everywhere to some degree, the researchers conclude. Perhaps 80 percent of the nonmicrobial species around Australia have not been described. Even in the Mediterranean, 75 percent of deep-sea species do not yet have names.

Deep waters below 200 meters are so underexplored that their life forms constitute “biodiversity’s big wet secret,” says the census’s chief scientist, Ron O’Dor of Dalhousie University in Halifax, Canada. Fewer than 10 percent of records of marine life come from the zone of abyssal plains between 4,000 and 5,000 meters deep, yet that zone accounts for half the oceans’ area.

To count fish, or even guesstimate abundance of the small proportion of known marine species, “you need a spread sheet,” Ausubel says. “And you didn’t have one.” So a major goal of the census has been to organize records of marine life.

The Ocean Biogeographic Information System database now allows anyone to look up what species have been found where. More than 90,000 of the species also have their own Web page in the Encyclopedia of Life.

Even though census scientists highlight how much is left to discover, they did a lot of exploring in 10 years. Out of the 17 teams that make up the census, 14 emphasized field expeditions, logging more than 9,000 days at sea sampling such places as seamounts or the Mid-Atlantic Ridge. More than 6,000 potential new species turned up, with 20 percent already confirmed.

These new explorations made a particularly big difference to the knowledge of life at the poles, which aren’t easy or cheap places to study, Ausubel says. Sending a ship exploring in Antarctica costs about $125,000 a day.

Among all the discoveries from the field, “what surprised me is the beauty,” Ausubel says. Census projects encouraged photography, and the stream of pictures over the years has introduced a wide public to the charms of deepwater crabs or free-swimming sea cucumbers.

Census workers also looked into the dark side of ocean studies, assessing how human activities such as fishing have changed marine populations. Delving into documents from monasteries or old tax records, researchers pieced together trends. Effects show up as far back as Roman times, researchers found. O’Dor, however, points out that the census also documents recoveries from human impact. “Under the right circumstances, the ocean is resilient,” he says.