Invaders musselling in

FOR decades, the Scottish blue mussel has been the choice ingredient for discerning diners feasting on moules marinières in London's top Michelin-starred restaurants.

Unrivalled for its quality and taste, the native mussel has reigned supreme in kitchens across the country.

But it can now be revealed that the Scottish-bred mollusc, mytilus edulis, is facing a twin threat from two "foreign" invaders. One is a French interloper which has steadily moved into northern waters as the seas have warmed up due to climate change.

But, astonishingly, scientists suspect that the second species which is posing a threat to Scotland's indigenous mussel industry may have survived unnoticed in an isolated pocket in a Scottish loch since the Ice Age.

DNA technology has been used for the first time to confirm that the species of mollusc, first found in the waters of Loch Etive on Scotland's west coast, is mytilus trossulus.

That is a type of mussel which, until now, had been found only in individual colonies stretching from the Arctic waters of North America to the Baltic Sea, the remnants of a widespread species that was disconnected during the Pleistocene Ice Ages that spanned from 1.8 million to 12,000 years ago.

The remarkable discovery has been made by Dr Ian Davis, a leading scientist at the government's marine laboratory in Aberdeen. He explained yesterday that until the DNA technology had been developed to identify individual species, it had simply been assumed that there was only one type of mussel in Scottish waters – mytilus edulis, the common blue variety.

But tests have now shown there are three distinct species inhabiting the waters of Scotland's west coast – mytilus edulis, mytilus trossulus and mytilus galloprovincialis, a Mediterranean mussel which has been developed for cultivation off the French Atlantic coast for many years.

And there are mounting concerns about the potential threat being posed by the trossulus because they have weak shells and poor meat yields. All three species are also interbreeding and producing hybrids to add to the confusion.

Said Dr Davis: "Mytilus galloprovincialis

migrated because the sea temperature was warmer. Good old climate change is what brought them here.

"But far more curious is the appearance of mytilus trossulus in our waters. We didn't think we had them at all. But we got reports from some of the shellfish farmers in the Argyll area, saying they were getting these mussels on their ropes which were a bit different in shape and they tended to have rather a thin shell and not to have very much meat on the inside."

He revealed: "We now know the trossulus are in Loch Etive. But how they got there is a really interesting question. There are two possibilities – one is that they have arrived on a yacht or a ship or whatever in which case they are immigrants. But the second possibility is that they might be a hangover from Ice Age times.

"It has been assumed that, after the Ice Age, as the seas warmed up, these mussels were shoved further and further north, leaving a little enclave in the Baltic. But there is an outside chance there might be another small enclave of leftovers in Loch Etive which have been there for thousands of years. We don't know quite what the answer is yet, but we are working on it."

Douglas McLeod, the chairman of the Association of Scottish Shellfish Growers, explained that mussel farmers on Loch Etive had contacted the marine lab because they were concerned about the "apparent changing nature" of some of their mussels.

And he said: "These findings could have implications for the industry as trossulus are a lower meat-yielding mussel species than either galloprovincialis or the blue mussel."

Mr McLeod added: "My understanding is that the trossulus species prefers less saline conditions. And I would not be surprised if the Ice Age theory was correct because the head of Loch Etive is very low in salinity at any time and therefore they could have survived there quite happily, I would have thought.

"It's not as if anybody had been looking for them."

Mussels have their own history

ACCORDING to legend, mussels have been cultivated in Europe since 1235 when Patrick Walton, an Irish sailor shipwrecked on the French coast, hung up nets in order to catch fish and found mussels attaching themselves to the poles supporting the nets.

The Scottish mussel industry is by far the biggest in Britain, producing up to 5,000 tonnes a year. There are now more than 50 companies growing mussels at around 300 sites, from Dunoon to Shetland.

The high zinc and iron levels and low calorie count of mussels have made them an increasingly popular choice with health-conscious diners.

Mussels can live up to 100 years and measure up to eight inches. And if kept moist and cold, mussels can live out of water for a week or more.

They extend a fleshy mantle outside the shell as a lure to attract fish and move around by attaching themselves to other creatures or by using a long, muscular foot they can stick out of the shell.

Mytilus galloprovincialis is native to the Mediterranean coast and the Black and Adriatic Seas. But it has now spread to the southern African coast and to Britain.

Mytilus trossulus can be found in the waters of Alaska and across to the Baltic Sea in Eastern Russia. Unlike many other mussel species, trossulus has three small teeth adjacent to the hinge.

Mytilus edulis is common all around the coast of the British Isles, with large commercial beds in the West of Scotland and Shetland as well as the Wash, Morecambe Bay and Conway Bay. The shape of the shell varies considerably according to local conditions and the colour varies from purple to blue to brown.