Invasive crab arrived by ship, flourishing in Icelandic waters

A new invasive species of crab is regularly being caught all around western Iceland, a decade or less after it first arrived in Icelandic waters.

The Atlantic rock crab is thought to have arrived in Iceland in the ballast water of ships. The crab grows quite big and is omnivorous. Little is known about how the species may continue to spread around Iceland or how it will interact with native flora and fauna. The crabs being caught in Hvalfjordur fjord are, however, said to be the same size as those caught in their native habitat off the east coast of North America. The Atlantic rock crab is not yet found anywhere else in Europe.

Halldor Palmer Halldorsson, the head of the University of Iceland research centre on the Sudurnes peninsula, told Visir.is that the first crabs were found in Hvalfjordur in 2006, but that it is quite likely it first arrived in around 2000.

“The crabs which have been caught are as big as some of the biggest caught in their natural habitat. The females also carry many thousands of eggs. The distribution seems to suggest that the animal is thriving,” Halldorsson says.

The Atlantic rock crab is being caught in Faxafloi bay and Breidafjordur, which is further north. In North America, the crab has a remarkably wide range — all the way from Labrador down to Florida.

The University of Iceland has been studying the invasive species since 2007, but researchers have yet to agree on a realistic stock size estimate around Iceland. “But it is growing, as can be seen from the female animals which carry tens, if not hundreds, of thousands of eggs. The rock crab now rules Hvalfjordur and more of them are caught there than any other crab species,” Halldorsson explains.

One of the biggest questions scientists are grappling with is what the species’ negative impacts will be on native creatures. The Atlantic rock crab is in direct competition with other crabs and is omnivorous like many other crab species. The rock crab not only competes for food but also eats other crab eggs and produces more of its own eggs than other species.

The University of Iceland research centre and the Marine Research Institute are working this summer with private companies Vatn og Sjor ehf. and Arctic ehf. on a project to tag Atlantic rock crabs. The project hopes to highlight the travels of individual crabs and provide information on overall stock size.

The male crabs often reach 14 centimetres wide, which is considered big and makes it a valuable crab on the seafood market. The crab is caught commercially in North America, but it is still too early to say whether Iceland has a commercially exploitable stock or not.