Rare shellfish discovery

The two Norwegian scientists could hardly believe their eyes on a dive on the far west of the coast of Spitzbergen in autumn 2004.

Right in front of NTNU Professor Geir Johnsen’s underwater camera a sensation was waiting for him: a colony of mussels had managed to attach itself to Sagaskjæret – the Saga Skerry – in Isfjorden.

Not since the early Middle Ages, when the climate enabled the Vikings to settle Iceland, Greenland and Newfoundland, have mussels established themselves as far north as Svalbard.

For mussels to survive they need temperatures well above those that have been normal in Norwegian arctic waters for the past thousand years. These shells were at least a year old, which means that they had survived at least one winter on the skerry, a fact that impressed the scientists even more than the find itself.

Media sensation

The discovery soon found its way into the columns of the local weekly “Svalbardposten”, then to international web-sites and news agencies. Journalists tended to present the return of the mussels as evidence of global climate change.

According to biology professor Geir Johnsen, however, the find in itself has no such significance.

“If we had found mussels on Svalbard for ten years in a row, it would have been different,” he says. But in the summer of 2005 the scientists found no mussels on Sagaskjæret. It remains to be seen whether they will find any this year.

Changing sea temperatures

Johnsen and his colleagues at the Svalbard University Centre, the University of Tromsø and SINTEF Fisheries and Aquaculture published their theories about the mussel find last autumn.

Referring to satellite and oceanographic measurements, they concluded that the return of the shellfish is due to oscillations in the temperature of the sea, given that the North-Atlantic Current transported unusually large volumes of water northwards in 2002 and 2003 and that this led to higher than normal surface temperatures west of Svalbard. In the summer of 2004, the water turned colder again.

The oceanographic measurements also showed that warm, highly saline Atlantic water found its way into Isfjorden in 2002 and 2003. The water was driven into the fjord by high northerly winds – such warm water is another prerequisite for the growth of the shellfish on Sagaskjæret.

Migration route recreated

Transportation of larvae from the coast of Norway by the North Atlantic Current is the only possible solution to the mystery of where these mussels came from. In Trondheim, SINTEF’s Dag Slagstad was ready to help his colleagues with the aid of a mathematical model of the ocean. Slagstad carried out simulations that showed that in the summer of 2002, mussel larvae drifting from the Vesterålen area would have managed to reach Svalbard in 60 days as “hitchhikers” on the current.

“This is at the very limit of the time that the larvae would have needed before they had to attach themselves to rocks. But some of them have obviously survived the trip,” says Professor Johnsen, who points out that the rare find is yet more evidence that biology is a finely tuned instrument.

“This find shows just how rapidly biological changes can take place when the external environment changes.”