If you thought the green crabs in Maine were bad, wait until you meet the ones from Nova Scotia.
A more aggressive form of the invasive species has been migrating south and is living in Maine waters. The Canadian crabs could make the green crab problem in New England even worse.
“They don't really belong in the Ecosystem here,” said Professor Markus Frederich, who teaches marine science at the University of New England. “They don't have enough predators, therefore they come in large numbers, and they are amazingly resilient from all kinds of stressors.”
Frederich said green crabs were first introduced to Maine 200 years ago from boats from southern Europe. The crabs have destroyed eelgrass beds, where many fish have nurseries and habitats. They feed on mussels and soft-shell clams, threatening the future of Maine’s commercial industries.
In the 1980s, a second green crab invasion happened in Canada with crabs from Northern Europe.
“Canadian green crabs inter-bred with Maine green crabs in Nova Scotia and formed a more aggressive type,” said Frederich.
Now, the Canadian green crabs are migrating south. Frederich estimates between two and four percent of all green crabs in Maine have the Canadian-genotype.
In the lab at UNE, scientists observed the Canadian crab’s behavior. When a researcher would put a finger into a tank, the green crabs from Maine would scurry, run away, and hide. But in the same experiment with the Canadian type, the crabs stick out their claws and charge.
“They actively attack people,” said Frederich. “We have literally seen them jumping out of the water to get at us.”
In another experiment, the researchers deprived the crabs of oxygen for 12 hours. They placed the Canadian crab on a small treadmill, and it “ran” for four minutes straight.
“As a scientist, I say ‘Wow, I wanted to find out why they can do that stuff,’” said Frederich. “As a regular citizen, I’m concerned.”
Frederich said the Canadian crabs can more quickly destroy eelgrass, prey on other fish, and cause coastal erosion. If the Canadian type continues to spread in Maine, it will only exacerbate an already precarious situation for fisheries like clams.
“It’s even more destructive,” Frederich said. “We are in even more trouble.”
The UNE researchers are planning to travel to Nova Scotia to retrieve more green crabs to study. They hope to learn more about the species in the next two years.