March 13, 2009 -- They are 8,000 miles apart, but the top and bottom of the Earth share a surprising number of species in common: 235 and counting.
"We think of the Antarctic and the Arctic as being united by ice but so far apart that we didn't think there was much commonality between them," said Russ Hopcroft, a zooplankton ecologist at the University of Alaska, Fairbanks. "The current count is 235 but will probably go up. That's remarkable, and it raises a lot of questions."
Hopcrofit is one of hundreds of researchers working to put together the first comprehensive list of which species live where in oceans around the world. The effort is part of a 10-year project called the Census of Marine Life. And the newly released comparison between polar regions was timed to coincide with the end of the International Polar Year.
One of the goals of the Census is to consolidate scattered tidbits and databases of what scientists already know. But researchers have also embarked on dozens of expeditions to collect new information --including a recent flurry of voyages to the poles.
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Those expeditions have uncovered some species that live elsewhere but had never before been discovered at the poles, along with other species that are totally new to science. On Hopcroft's last cruise to the Arctic, for example, he and colleagues used remotely operated vehicles to double the number of known species of sea gooseberries (a type of zooplankton) from five to 10.
So far, about 5,500 marine species have been catalogued in the Arctic and 7,500 in the Antarctic. The 235 species that appear on both lists range from whales to birds to microscopic invertebrates. Data analysis is ongoing, as is the search for more species.
"We are now reaching a stage of scientific consensus about this number," said Rolf Gradinger, a biological oceanographer at the University of Alaska, Fairbanks. "It will certainly still change over the next decades."
As counting continues, scientists are trying to explain how each of the 235 species got to both ends of the Earth.
Deep ocean currents probably transported small species that live on the seafloor, Gradinger said. Birds and whales, on the other hand, can migrate long distances on their own. And some species may date back to a time when the Earth was an entirely different place, before the continents shifted to their current locations and the climate became what it is today.
"It's more than just: Here's a number," Hopcroft said. "Knowing the size of the number and who are the animals on the list will allow us to pursue some more interesting questions."
With DNA analysis, for instance, scientists hope next to determine whether species that look the same actually are the same. The results of these studies could also reveal how long polar populations have been separated from each other, and how long it took them to split. In turn, that kind of information could help reveal fundamental facts about the history of the Earth, the oceans, and the environment.
"The polar seas are at the extreme ends of the entire range of marine habitats," Gradinger told Discovery News. "We need to know how many of these life forms are unique to the polar seas to understand the impact of changing environments and human exploitation in these seas."
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