Melting Arctic could cause mollusks to migrate

Mollusks from the Pacific could march into the Atlantic Ocean within decades because of the melting of Arctic sea ice, researchers in California say.

HALIFAX — Mollusks from the Pacific could march into the Atlantic Ocean within decades because of the melting of Arctic sea ice, researchers in California say.

For mollusks to pass, the Arctic would need to have less than 75 per cent sea-ice cover for 125 consecutive days — something that could happen around 2050, according to an estimate two years ago by the Intergovernmental Panel on Climate Change.

But Peter Roopnarine, curator of geology and paleontology at the California Academy of Sciences in San Francisco, says that could happen sooner.

“We could be looking at between 2020 and 2030,” says Roopnarine.

Roopnarine and Geerat Vermeij, a geologist and evolutionary biologist at the University of California, Davis, say Pacific-to-Atlantic migration is probable for all kinds of sea life, including fish, crabs, sea stars, sea urchins and seaweed.

They base much of their theory, which first appeared in the scientific journal Science last year, on fossil records from the last time mollusks traversed the Arctic: about 3.5 million years ago.

At the time there was a shift in climate, which kept the Bering Strait open long enough to allow hundreds of species, such as mollusks, cod and herring, to migrate from the Pacific to the Atlantic over the ice-free Arctic.

Some of the species became extinct, but others colonized the Atlantic and continue to populate its waters today.

Roopnarine says a similar phenomenon is in the offing.

“A lot of fish, for example, are certainly going to be part of this invasion,” he says.

“It’s going to change the entire composition of the Northwest Atlantic ecosystem.”

Roopnarine said this migration could bring new fisheries to Atlantic Canada.

He added that it’s possible some species would be able to make the journey in one summer, though most would move through the Arctic waters more gradually.

The entire journey, he predicts, would take “at most a few years.”

Depending on their size, mollusks may arrive in a number of ways, such as being carried by currents, crawling, and floating on seaweed or logs, Vermeij says.

He says most creatures would travel eastward because of currents and Pacific species tend to be larger, therefore more able to cross the Arctic Ocean.

Those that cross would likely stay in the Northwest Atlantic because waters east of that area are too warm, Vermeij says.

There is evidence that a modern-day inter-oceanic migration may have already begun.

In 1999, British oceanographer Chris Reid discovered a microscopic Pacific plant known as the Neodenticula Seminae diatom in the Atlantic Ocean which has since settled and spread throughout Northwest Atlantic waters.

Reid says the plant was in the North Atlantic until 800,000 years ago, when waters became too cold for it to survive.

Reid and other researchers from the Hardy Foundation for Ocean Science in England concluded that the plant travelled from the Pacific over Arctic waters into the North Atlantic.

In 1998, Arctic ice retreated to the north of Alaska and Canada for the first time on record, leaving open water all the way from between the Pacific to the North Atlantic, Reid says.

“So, it fits the story really well,” he says.

The only other plausible theory, says Reid, is that the diatom came from a ship’s ballast water. But he doesn’t think that’s likely because ships do not discharge their water in the middle of the ocean, where they found the plant.

Since it’s discovery, the plant has spread from the Labrador Sea down the East Coast. A large concentration was found in the Gulf of St. Lawrence in 2001.

Michel Starr, a scientist with the Department of Fisheries and Oceans, said the ecological impact of the plant on the North Atlantic coast has not yet been determined.

Starr says it is still present in the Gulf of St. Lawrence but there are less than there were in 2001. He said he doesn’t know why.

Starr believes more organisms will follow the plant’s route, which will carry implications on current life in the Atlantic Ocean.

“We can expect a reorganization of the North Atlantic ecosystem,” says Starr.

While some invasive species, like the European green crab, have displaced native species along both coasts of Canada, Vermeij is not worried about the mollusks having the same effect.

“They’re not going to eliminate the Atlantic species,” he said.

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