Dozens of species common to both polar seas — separated by nearly 11,000 kilometers have been discovered by researchers from the Census of Marine Life. "We think of the Arctic and Antarctic as similar habitats but they are separated by great distances. So finding species at both ends of the Earth — some of which don't have a known connection in between — raises a whole bunch of evolutionary questions,"
Researchers cautioned that more work needs to be done to confirm whether the species are indeed the same or differ genetically.
There are a number of possible explanations of how similar species live so far apart.
Some may have traveled along the deep-sea currents that link the poles. Although there was 12,000km separating the two habitats, it did not create a huge barrier for marine wildlife, as a mountain range does for terrestrial species. Temperature differences in the oceans did not vary enough to act as a thermal barrier.
There is continuity in the ocean as a result of the major current systems, which we call the 'conveyor belt'; a lot of these animals have egg and larvae stages that can get transferred in this water. The oceans are a mixing ground. There are all kinds of currents that allow things to move around.
Or the creatures may have thrived during the height of the last ice age about 20,000 years ago when the polar environment was expanded and the two habitats were closer.
One result of the sea-life census: Researchers are beginning to understand how the polar seas act as incubators for life that sometimes ventures away from the poles as sea temperatures rise and fall over the eons.
Last year they discovered that several octopus types have repeatedly colonized the deep sea, each migration coinciding with retreating Antarctic ice over 30 million years.
The scientists now theorize that the Antarctic regularly refreshes the world's oceans with many new creatures, including different varieties of sea spiders, isopods (crustaceans related to shrimp and crabs), and more. They believe the new species evolve when expansions of ice cloister around the south polar region; when the ice retreats, creatures radiate northward along the same pathways followed by the octopuses.
Meanwhile, the census finds smaller marine species are replacing larger ones in some Arctic waters. The reasons are unclear but the implications for the Arctic food web may be profound, the scientists said.
The Census is seeking to lay down a benchmark for judging long-term shifts in the oceans. The U.N. General Assembly has asked for regular assessments of the oceans to gauge the impact of pollution, over-fishing and climate change. The 10-year project involving researchers in more than 80 nations aims to chart the diversity, distribution and abundance of life in the oceans.
The team estimates there are 7,500 animals in the Antarctic and 5,500 in the Arctic, and the total number of marine life species known globally is about 250,000. That number may eventually rise to about a million, scientists say. In general, other scientists have said they do not know how many species exist on Earth. The National Science Foundation estimates there could be anywhere from 5 million to 100 million species of life on the planet, but science has only identified about 2 million.
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More about the Census of Marine Life.