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BIDDEFORD, Maine – Canadians are known as friends, but these fearless brutes who migrate from Canadian waters are better suited to the hockey arena.
The green crabs of Nova Scotia are the same as their cousins who already inhabit the waters of Maine, but they are rougher and threaten to accelerate damage to the coastal ecosystem by engulfing clams and by destroying the native grass.
The docile green crabs are disappearing from a threat, while newcomers are more likely to shake their tongs and load.
"What we see is this level of insane aggression," said Markus Frederich, a professor at the University of New England.
They are each genetically distinct.
The new variant of crab from northern Europe is more resistant and adapted to cooler waters than the more docile crab from southern Europe.
Green crabs, even the most docile, are considered a plague that can devour soft-shell clams and juveniles. They can destroy the eelgrass that is a hiding place for juvenile sea creatures.
But Canadian crabs are taking a new step.
Louis Logan, a graduate student from the University of New England, had the unpleasant task of labeling captured crabs in Nova Scotia waters for research.
The crabs were not in the mood for games.
At a distance of 5 feet, the pint size brutes, which measured 4 to 5 inches in diameter, took up a fighting position. Those who caught it were not in a hurry to let go.
"Every time I went to get one, they came to get me," he writes in an email.
One of them, in particular, would jump out of water in his attack frenzy.
In the lab, the researchers unleashed both types of crabs on an eelgrass bed in a saltwater pool, and the difference was striking. Canadian invaders have shredded eelgrass like Edward Scissorhands in their efforts to reduce marine life seeking refuge, Frederich said.
The first series of studies focused on 200 crabs in Canada and will be published in the coming months.
Other studies will focus on whether a specific gene plays a role in aggression or whether a factor called hybrid vigor is at stake, he said. Hybrid vigor theory suggests that crabs may be more aggressive as they become established, but will disappear later.
The quarrelsome newcomers currently only account for about 2 to 3 percent of the green crabs crawling on the bottom of the ocean off Maine, but these numbers will certainly increase, Frederich said.
"It will be a totally different ball game," he predicted. "It's just a question of when more crabs are competing with Maine's green crabs."
The docile green crabs have been around for more than a century in the waters of New England, but they have emerged as a major problem with the warming of the Gulf of Maine. The largest crabs arrived off Nova Scotia in the 1980s and currents brought their larvae south into New England waters.
Finally, newcomers will go further south. "We can not do anything about it," he said. "The only thing we can do is learn to live with."
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