Green crabs have earned themselves the nickname “cockroaches of the sea” in the scientific community, and in recent years – since hitching a ride from Europe & Africa to Atlantic Canada on ships – they’ve been pains in the asses of local lobsters and fishers, and those of us who love Atlantic Lobster.
The Green Crab is a small little thing that hangs out in sheltered shorelines, and has a pukey green colour awash in the standard crab orange (hence their name).
They’re aggressive predators for their size, and gobble up clams, mussels, oysters, smaller crabs, and other crustaceans, and even small fish. In other words, they eat the kind of stuff our native species, like lobster and snow crab, want to eat.
Like an uninvited party guest, they’re theoretically capable of eating our lobsters out of house and home, and making a mess of their natural environment. In addition to taking a literal bite out of lobsters’ food supply, green crabs can destroy the habitat of shellfish like oysters, scallops, and clams as they tear about like devilish tornadoes.
To the ire of fisher people in Atlantic Canada, green crabs can also spread their parasites to other shellfish, like lobster. One of these parasites, Profilicollis botulus, actually affects a lobster’s behaviour by making them either dumb or brave enough to be oblivious to predators, and therefore more susceptible to predation.
Nicola Zargarpour, a graduate student at MUN’s Marine institute, recently received an RDC Ocean Industries Student Research Award to investigate the matter. Zargarpour confirms that lobster fishers have noted reduced catch rates in some invaded areas, but she says mechanism by which this reduction could occur is still unknown, “which makes it challenging to implement responses within the fishery.”
She says “there are concerns and anecdotal accounts by fish harvesters, and one hypothesis is that this decline could have been exacerbated by the green crab invasion, given the explosive rate that they are able to establish.”
To quote DFO, “It is impossible to wipe out green crabs once they are established in an area.” They reproduce too quickly and plentifully to get ‘em all. Females release up to 185,000 eggs once or twice per year. They’re actually one of the 10 most unwanted species in the world, and they can expand their range up to 100 kilometres in one year.
Zargarpour says the ultimate focus of her research is to investigate whether green crab directly impact lobster catch at the level of the gear. “To do this we are using underwater cameras attached to lobster traps to observe interactions between green crab and lobster in and around lobster traps as they soak in the water.”
She’s currently in the process of analyzing all the underwater video — nearly 200 hours worth! “We hope to tease apart some of these questions.”
Green crab first started showing up in Canadian waters in the 1950s, around southwest New Brunswick, and have been expanding their presence throughout Atlantic Canada ever since. They made their way to us here in Newfoundland in 2007. They spread best across the world by having their larvae get in ballast water under boats. On account of their long larval stage (50 to 80 days) they can catch a lengthy lift in their pre-crab, larval life form before emerging as crabs.