Ocean temperature oscillations enable reappearance of blue mussels Mytilus edulis in Svalbard after 1000 years of absence

We report the first observations of settled blue mussels Mytilus edulis L. in the highArctic Archipelago of Svalbard for the first time since the Viking Age. A scattered population wasdiscovered at a single site at the mouth of Isfjorden in August 2004. Our data indicate that most mussels settled there as spat in 2002, and that larvae were transported by the West Spitsbergen Current northwards from the Norwegian coast to Svalbard the same year. This extension of the blue mussels’ distribution range was made possible by the unusually high northward mass transport of warm Atlantic water resulting in elevated sea-surface temperatures in the North Atlantic and along the west coast of Svalbard.