The Bright Side of the Green Crab

What is distinctive is its spiked shell that tapers at the top into 13 spines, like a crown worn by the leader of an invading army—which is appropriate enough, since the second thing you need to know about the green crab is that it’s one of the planet’s most aggressive invasive species.

Their aggression extends beyond people; wherever they’re found, green crabs snip and uproot marine plants such as eelgrass and dig into sand and mud in their search for prey, which includes small fish, clams, mussels, and even each other.

Then, in the 1980s, a second introduction occurred on Nova Scotia’s Atlantic coast, in a sliver of land that makes up part of Kejimkujik National Park, known locally as Kejimkujik Seaside.

Yet that introduction didn’t register as cause for serious concern until decades later, when researchers conducted surveys of the park’s estuarine beds of eelgrass—a habitat that provides a nursery for a broad range of species.

“That was the smoking gun,” says Beaulieu.

By this time, the green crabs in the park were no longer the same as those that had arrived in the 1980s.

Researchers and fishers use baited traps to capture green crabs.

“That meant that … perhaps we were able to control the green crab population enough that those juvenile clams that are just below the surface of the , are no longer being as heavily impacted,” she explains.

And in recent years, researchers and restaurateurs in New England have drawn on the expertise of those fishers to launch a green crab fishery.

“Historically across North America, if people start eating something or using something, likely those populations are going to suffer,” she says.

Park officials supplemented these excursions with school trips, where students were invited to hunt green crabs in the estuary on foot at low tide, and with public presentations at the dock in the estuary, and in the surrounding communities, on the risks posed by the species.

In 2015, Roy swapped his eel license for a green crab one, after realizing his eel traps were coming up full of the crustaceans.

For Roy, the part he’s been playing in allowing ecosystems to regenerate is itself a kind of renewal; in 2012, he lost his job of 26 years when the local newsprint mill shut down, and he turned to fishing instead.

Moores’s lab’s innovation was a process of creating chitosan that did away with those corrosive chemicals and that produced a non-water-soluble form of the polymer, which could be used in everything from plastic biomedical implants to plastic packaging.

This year, a postdoctoral researcher in Moores’s lab has started to investigate the application of this method on green crabs caught in Kejimkujik and shipped frozen to Montreal, Quebec.

A separate research partnership between Parks Canada and Dalhousie University in Nova Scotia is investigating the possibility of using green crabs to produce a concentrated liquid fertilizer for houseplants and gardens.

Taken together, Beaulieu says these measures are not intended to eradicate green crabs from the ecosystems they’ve invaded; in talking with Mi’kmaw partners in the park, Beaulieu says park officials have come to appreciate such a strategy is not practical.

“Our thinking is, we’re allowing the ecosystem to adapt,” says Beaulieu.

Moira Donovan is an independent journalist and radio producer based on the East Coast of Canada, with a body of work focused on the environment and climate change.

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