John Roach, National Geographic News 8 Aug 08;
North Pacific shellfish—including snails and other mollusks—may blaze a path across the Arctic Ocean to the North Atlantic if the sea ice melts in coming decades as predicted, a pair of scientists said today.
Mollusks traveled the northern passage when the Arctic was last ice free, about 3.5 million years ago, during a warm stage of the Pliocene, which spanned 5.3 to 1.8 million years ago, the scientists say.
The Arctic route was cut off when temperatures cooled, starving the ocean of phytoplankton—the floating plants that mollusks need to survive, explained Geerat Vermeij, a geologist at the University of California at Davis.
Current climate models suggest the Arctic will be ice free by 2050. In that scenario, conditions would be similar to those during the mid-Pliocene, and the mollusk migration would resume, the scientists say.
The floating plants make the Arctic like a highway lined with fast-food restaurants, allowing the mollusks to eat their way from the Pacific to the Atlantic, Vermeij said.
"You provide enough nutrition both for the larval stages and, in fact, for fast-growing adults, which [have] a high demand for easily available food," he said.
Vermeij and California Academy of Sciences colleague Peter Roopnarine predict the migration in commentary published in tomorrow's issue of the journal Science.
One Way Trek
According to Vermeij, the invasion will be one-way, with mollusks, as well as algae, fish, barnacles, and other creatures likely to move from the Pacific to the Atlantic.
More water flows northward from the Pacific through the Bering Strait than flows the other way, Vermeij said, explaining why the migration will move in that direction.
The North Pacific, furthermore, teems with marine life that is well adapted to fight for survival in the sparse conditions of the Arctic, he said.
By contrast, North Atlantic marine life is less diverse and less fit.
Still, the invasion is unlikely to cause extinctions in the North Atlantic, he said.
There is no evidence of invasion-spurred extinctions from the migration in the mid-Pliocene, he noted.
And generally, the oceans have plenty of room for native species to hide from the invaders. Even if some are killed, at least a few will survive, the scientists said.
Invasion Consequences
The authors believe the invasion will enrich North Atlantic biodiversity by adding new species and creating new hybrid species as well.
James Carlton, a marine ecologist at Williams College in Williamstown, Massachusetts, noted that a type of algae called diatom made the trek across the Arctic in 1998.
Now larger species appear poised to make the journey within a few decades, he said. And while the Pacific invaders may not cause extinctions, they could lead to "rather striking changes in the abundance of certain species."
The consequences of the changes, however, are unknown.
"We'll just have to see who shows up on the other side," he said. "That will be absolutely fascinating."
