New study finds multiple invasions increase green crab's Canadian range

Using molecular tools, biologist Joe Roman, conducting research at Harvard University's Department of Organismic and Evolutionary Biology, found that it was the injection of new lineages in northern Nova Scotia that was responsible for the crab's success in the north.

Roman's article, “Diluting the founder effect: Cryptic invasions expand a marine invader's range” will be published in the online edition of Proceedings of the Royal Society B: Biological Sciences on June 21, 2006.

The green crab has long been a resident of North America. A native of Europe, it was probably released among the ballast rocks of ships crossing the Atlantic around the time of the American Revolution. Since the 1950s, its spread has stalled in Nova Scotia; the waters off Cape Breton and the Gulf of Saint Lawrence were thought to be too cold for the species' survival.

In recent years, however, a rapid expansion around Cape Breton and north to Prince Edward Island and the Magdalen Islands of Quebec had fish and wildlife managers concerned about impacts on local fisheries and native crabs.

The DNA used to track this invasion suggests that these northern crabs constitute a new invasion front, which may have arrived in the waters around the Strait of Canso through shipping from the North Sea. The new invasion has been surprisingly successful in the Gulf of Saint Lawrence.

“These multiple invasions are happening all over the world,” Roman says, “and many of them go undetected.”

Using DNA, biologists have uncovered cryptic invasions among such prominent invaders as zebra mussels and the brown algae Undaria. According to Roman, “It's clear that the pressure of these multiple invasions is having a devastating effect on our waterways.” Invasive aquatic species can be released through ballast water, aquaculture, aquaria, and even live seafood.