Penguins and polar bears may stay at opposite poles, but scientists surveying marine life in the Arctic and Antarctic have found many other species – 235 so far – that live at both ends of the Earth.
The pole straddlers include crustaceans with sword-like antennae and swimming snails that look like tiny angels. There are also shrimp, worms and snails that spin a net of mucus to catch algae.
Over hundreds of centuries, populations of these small, cold-water creatures slowly drift back and forth between the poles via deep currents that act like conveyor belts, said Russell Hopcroft, a Canadian researcher involved in compiling the first marine-life census of the planet.
It involves 2,000 researchers from 82 countries in an unprecedented effort to document and track the life forms that inhabit the oceans. The census began in 2000, and will be released in October, 2010. On Sunday, the scientists announced what they have discovered during sometimes perilous voyages to the Arctic and Antarctic as part of International Polar Year, 2007-2008.
It is well known that some larger species, like grey whales and Arctic terns, travel back and forth between the Arctic and Antarctic.
But Dr. Hopcroft, who works at the University of Alaska, said he and his colleagues were surprised to find that so many other species live at both poles.
The northern and southern versions of these animals look the same, he said, although genetic tests may show them to be distinct.
Individual creatures don't make the pole-to-pole voyage. The journey is intergenerational and the round trip can take 600 to 1,600 years, Dr. Hopcroft said. The currents that carry them are one to two kilometres below the surface.
“It is not that the same individual moves from the pole to pole … but the population is continuous,” he said.
Last year, census researchers found that the world's deep-sea octopuses originate in the Antarctic.
They are now investigating whether many cold-water species evolved first in the deep, dark waters around the South Pole, and then spread to other parts of the world.
So far, they have identified 7,500 animal species that live in the Antarctic and 5,500 in the Arctic.
In some Arctic waters, they found that smaller marine species are replacing larger ones, which may have profound implications for the northern food chain.
Arctic clams, snails, crustaceans and plankton are generally bigger than close relatives that live in less icy waters, Dr. Hopcroft said.
It seems the larger, northern species are being pushed out. This means that predators, like birds or mammals, have to work harder to find more smaller shrimps or clams to eat.
Working conditions for the census scientists can be difficult. Biologists in the Antarctic faced waves that were 16 metres high.
In the North, they sometimes needed an armed lookout to keep an eye for polar bears.
They are mapping the range and distribution of animals in the oceans, the diversity of species, their abundance and how that has changed over time. They plan to produce a scientific volume, but also a coffee-table book and a children's version.
They consulted with monastic and government records to reconstruct walrus populations in the Russia's White and Barents seas.
They have used narwhals as mobile weather stations by attaching tracking devices to the animals, which have a single, unicorn-like tusk.
This gave them information on the distribution of narwhals, said Ron O'Dor, a Canadian biologist who is one of the senior scientists in charge of producing the census.
But it also provided data on temperature and salinity in parts of the Arctic Ocean the researchers haven't been able to reach.
“They go to places that no one else goes,” Dr. O'Dor said.
The researchers are now synthesizing the results of work done all over the world, including seafloors in the Antarctic that were exposed to light for the first time in 100,000 years after an ancient ice shelf collapsed and disintegrated.
Some of the most startling discoveries have been in the polar seas, including a pink octopus close to the North Pole and scores of strange jellyfish and gelatinous organisms that thrive without light beneath the Antarctic ice.
This year, there are plans for a cruise to the Beaufort Sea to investigate the role ice ridges could play as a refuge for marine life if the Arctic sea ice continues to shrink because of rising temperatures.
A trip to study the world's deepest known ocean volcanoes has also been scheduled. They are found more than 5,000 metres below the surface of the Caribbean Sea between Jamaica and the Cayman Islands.
A team will also head to largely unexplored areas of the Indian Ocean near Madagascar, where researchers expect to find hundreds of new species.
Local lobster fishermen have offered collectors strange mollusk shells that appear to be unique to the area.
