What is the Differential Undercount in the Census of Marine Life?

The first ever census of marine life has recently been completed, more than a decade after it was first conceptualized, and after the expenditure of $600 million and the participation of nearly 3,000 scientists. 

With sound, satellites, and electronics, some- times carried by marine life itself, the Census tracking of thousands of animals mapped migratory routes of scores of species and charted their meeting places and blue highways across the interconnected ocean. The tracking measured animals’ surroundings as they swam and dove and revealed where they succeed and where they die. The Census found temperature zones favored by animals and saw the immigration into new conditions such as melting ice.

The results remind us that we are not that dramatically different from other animals in many respects. Two things stand out among the findings. The first is that marine species have migrated all over the global waterways, and have populated all corners of the sea, just as humans have spread around to find the habitable portions of land. Indeed, some species are very nomadic:

The census also highlighted marine life that makes commutes that put a suburban worker's daily grind to shame. Before the census started, the migration of the Pacific bluefin tuna had not been monitored much. But by tagging a 33-pound tuna, scientists found that it crossed the Pacific three times in just 600 days, according to Stanford University's Barbara Block. A different species of tuna, the Atlantic bluefin, migrates about 3,700 miles between North America and Europe. Humpback whales do a nearly 5,000 mile north-south migration.

The second really interesting finding has to do with the genetic similarity of marine life:

The census found another more basic connection in the genetic blueprint of life. Just as chimps and humans share more than 95 percent of their DNA, the species of the oceans have most of their DNA in common, too. Among fish in general, the snippets of genetic code that scientists have analyzed suggest only about a 2 to 15 percent difference, said Dirk Steinke, lead scientist for marine barcoding at the University of Guelph in Canada.

As is true with censuses of humans, not every marine creature could be counted:

After all its work, the Census still could not reli- ably estimate the total number of species, the kinds of life, known and unknown, in the ocean. 

But that is hardly a criticism of an effort that has generated so much new information:

Now anyone can see the distribution of a species by entering its name at iobis.org, a Web site that accesses the names and “addresses” of species compiled in the Census’s global marine life database.