August 11, 2008
Monday

Pacific Ocean shellfish -- the mussels and snails, the clams and cockles -- are heading for a mass invasion into the North Atlantic that could alter the entire ecology of both oceans as sea ice vanishes from the warming high Arctic, two California scientists predict.

It has happened at least once before, the scientists say -- about 3.5 million years ago, when a relatively brief period of natural global warming kept the Bering Strait open and hundreds of species of marine life migrated from the Pacific through the ice-free Arctic Ocean to colonize the Atlantic. The genes of many animals -- both shelled and finned -- formed hybrid species after that long-ago invasion during the Pliocene epoch.

Geerat J. Vermeij of University of California Davis and Peter D. Roopnarine of the California Academy of Sciences in San Francisco describe what they call "the coming Arctic invasion" in the current issue of the journal Science.

According to climate models of the Intergovernmental Panel on Climate Change, which monitors global warming and its effects, the Arctic Ocean will become virtually ice-free by 2050 as global warming continues. And many climate experts and scientists, including Vermeij and Roopnarine, calculate that it's likely to be under way in little more than 20 years.

In fact, there's evidence that some of that invasion from sea to sea by more primitive organisms has already begun, but the other way around -- in this case, from the Atlantic to the Pacific.

British oceanographer Chris Reid of the Hardy Foundation for Ocean Science in Plymouth was monitoring tiny creatures called diatoms in the waters of the long-familiar Northwest Passage nine years ago. He discovered a species of diatoms in the Northwest Atlantic that had never been seen there before but is native to the northern Pacific.

Diatoms are one-celled plants and are the most common organisms in the masses of oceanic plankton that make up the basis of the oceans' food webs and the entire ecology of the seas. The species Reid spotted is called Neodenticula seminae, and an article in the journal Nature quotes Reid saying: "We were very familiar with the species in the Pacific, but we had never seen it in the Atlantic before -- it took awhile for us to realize the significance."

In an interview, Vermeij (pronounced Vair-may) said that neither he nor Roopnarine had been aware of Reid's 1999 discovery when they reached their own conclusions from the fossil evidence of the ancient invasion and from current DNA studies of varied shellfish species in both oceans.

"But it looks like the invasion may have already begun," Vermeij said.

Studying the fossils of marine organisms from 3.5 million years ago, the two California paleontologists saw that water from the Pacific Ocean must have been flowing north through the Bering Strait and into the Arctic Ocean where the ice had cleared and food was abundant. From there, hundreds of Pacific marine species moved into the warm North Atlantic to "colonize and enrich" the sea there, Vermeij and Roopnarine concluded.

"But a million years later the ice age returned in the far north and put an end to all of that," Roopnarine said. "The Arctic Ocean, covered densely with ice again, became virtually a desert."

Now that the northern seas are warming and a new mass migration of marine species is in the offing, "there's a fair likelihood the invasion might generate new fisheries," Roopnarine said. "Extinctions are unlikely, and there might be a cascading increase in abundance, perhaps, but that's not easy to predict."

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