The European green crab that jeopardizes Maritime fisheries likely benefited from multiple invasions introducing new genetic lines to the population, a new study suggests.

The crabs were first introduced to North America in the 1950s. In recent years, they have rapidly expanded their range around Cape Breton, north to Prince Edward Island and the Magdalen Islands of Quebec.

The green crab has no natural enemies. It has been eating its way up the coast, feeding on clams, oysters, mussels and small fish.

Fish and wildlife managers are concerned about how the marine invaders could hurt local fisheries and native crabs.

"It's clear that the pressure of these multiple invasions is having a devastating effect on our waterways," said study author Joe Roman, a biologist working at Harvard University in Cambridge, Mass.

When the green crab first invaded the Gulf of Maine, the softshell clam fishery was affected, he said.

Biologists wondered if climate change or an adaptation to cold were responsible for the expansion.

Roman's study raises another possibility.

The crab's northern success could be thanks to new lineages added to northern populations in Nova Scotia that may have adaptations that allow the species to persist in a wider range of environmental conditions, said Roman.

"Canadian populations have higher genetic diversity than southern populations, which strongly suggests that multiple introductions have occurred in the Maritimes since the 1980s," Roman wrote in Wednesday's online issue of Proceedings of the Royal Society B: Biological Sciences.

The invasive front may have arrived around the Strait of Canso through shipping from the crab's native range in the North Sea, the study said.

A ship's ballast discharge can hold a wide range of species, which could account for the genetic diversity, he said.