Invasion of the giant oysters

Since its introduction in the 1970s, the Pacific oyster has spread like a plague, killing mussels, threatening birds and now even tourism. Tony Paterson reports from Germany on another worrying sign of global warming

A A A

Professor Karsten Reise does not normally use the sort of emotive language found in Hollywood horror movies. He is a serious and highly informed marine biologist in his late fifties who has been researching the environment around Germany's North Sea island of Sylt for well over a decade.

But on a grey and sea mist-bound afternoon, the heavily bearded professor walked over to a shelf in his office at Sylt's Alfred-Wegener Polar and Marine Research Institute overlooking the island's tidal sand flats and removed what looked like some ghastly freak of nature.

The remains of the creature in question was a giant barnacle-covered shell almost three times the size of an adult male's hand, yet shaped in the unmistakable form of an oyster. "This is the monster I found on the sands out there about four years ago," Dr Reise said, waving his arm in the direction of the sea. "Since then, the oyster phenomenon has turned into a proper invasion," he added.

Giant oyster specimens are not the only factors that seem to have induced uncomfortable feelings of Metro-Goldwyn-Meyer-style panic on Germany's northernmost island. Even the academic literature on the subject speaks unreservedly about an apparently unstoppable "invasion" by an "alien species" of the island's protected tidal sand flats.

Sylt's alien is the Crassostrea gigas, or Pacific oyster, which currently accounts for about 90 per cent of all oysters consumed globally.

The Pacific oyster was introduced to European coasts in the 1970s from Japan and British Columbia following the virtual collapse of the Continent's native oyster industry. The Pacific oyster was not introduced to Sylt, which boasted a formidable pre-war oyster industry, until 1986, and then only as a product that would be carefully farmed in an environment controlled partly by man.

"The Sylt oyster producers were granted a licence to fish farm, but back then all of the experts were convinced that the waters around the island were far too cold in winter to enable the oysters to survive without human intervention," Dr Reise said. But in the meantime, the experts have been proved hugely, even alarmingly, wrong.

The scale of Sylt's oyster invasion is massive. The Alfred Wegener Institute first noticed that something unusual was happening on the island's protected tidal sand flats back in 1995 –nine years after the Pacific oyster was introduced at a lone oyster farm on Sylt's northernmost tip. Handfuls of wild Pacific oysters were found that autumn nestling on an indigenous blue mussel bed that was exposed at low tide.

At that stage, the island's marine biologists were not unduly surprised. A few wild, or feral, oysters were expected as a natural byproduct of the local oyster farm. In 1995 the feral Pacific oyster population was about one oyster per square metre of tidal sand flat on Sylt. By 2004 the figure had leapt to nearly 500 per square metre. By 2007 the island's feral Pacific oyster count jumped to a staggering 2,000 per square metre. "What we are now experiencing is exponential growth of the wild oyster population," says Dr Reise. "We don't yet know where the process will end."

At low tide out on the wind and wave-beaten expanses of sandy mud and seaweed, evidence of the island's oyster invasion is everywhere. Pairs of oystercatchers and the occasional Brent goose spring into flight from sands that are covered for almost as far as the eye can see with a carpet of feral oysters that crunch underfoot. Unlike those consumed in posh restaurants, these are stuck together in vast clumps made up of scores of small oysters, with the odd native blue mussel and winkle nestling in between. "Six or seven years ago there was nothing here but sand," Dr Reise said.

Marine biologists are unanimous in their explanation for the causes of the Pacific oyster invasion. Sylt, which is on the same latitude as Newcastle, used to experience temperatures that were low enough to freeze the shallow salt waters surrounding it during winter. But the last harsh winter on Sylt was at the beginning of 1996. Since then, the island has experienced nothing but mild winters. "Cold winters can bring the spread of wild oysters to a halt, but warm winters enable the oyster larvae to flourish," said Dr Reise. "Their increase is a direct result of global warming."

During the warmer-than-average summer experienced in northern Europe during 2006, the sea temperature was greatly increased and the warm water appears to have encouraged an explosion in Pacific oyster larvae. In its wild form, the oyster has managed to spread as far north as Bergen in Norway.

The experts are not sure whether the current oyster explosion will have serious environmental consequences. During the early stages of the invasion, oysters were found almost exclusively on Sylt's indigenous blue mussel beds, raising fears that the rising oyster population would kill off the mussels.

Seabirds that normally rely on mussels as a food source have also been affected. Eider ducks, which used to visit Sylt on a regular basis in winter, have all but disappeared. The oystercatcher, a wading bird that lives all year on the island, also relies on mussels to survive, despite its name.

Even tourism is affected. Visitors who used to enjoy strolling across the sands in their bare feet now risk injury on the razor-sharp shells that cover the Pacific oyster beds.

Sylt's lone oyster farm, Dittmeyer's Oyster Company, has been farming its "Sylter Royal" Pacific oysters in one of the island's bays since 1986. Mr Dittmeyer insists that the sudden invasion of wild oysters on Sylt simply shows the island is catching up with much of the rest of northern Europe, where the Pacific oyster dominates. "It is happening everywhere," he said.

Mr Dittmeyer started his oyster farm on Sylt with Pacific oysters imported from Colchester. It was a case of history repeating itself. The Danish King Knut the Great did exactly the same during the 11th century, when he imported shiploads of oysters from England to what is now Germany's north-west coast.

As in much of the rest of Europe, the inhabitants of Sylt were able to harvest oysters from the seabed for the next 900 years, until industrial fishing and disease rendered them virtually extinct. Marine biologists such as Dr Reise say that today's explosion of the wild Pacific oyster population is just one of global warming's effects. Nobody has been able to predict its consequences. One of the factors that makes the spread of wild oysters almost impossible to control is the fact that the creatures have no natural predator – yet.

In his office, Dr Reise has another shell that sits next to his monster Pacific oyster. It is a black and grey speckled conch about the size of a large fist that houses a large sea slug or snail called the Rapana, which is found in Japanese waters. The creature is capable of boring through the shell of a Pacific oyster. "It was introduced in the Black Sea and has since spread to the Mediterranean," the professor said. "It could conceivably be introduced in the North Sea."

Suggested Topics
News
Young Winstone: His ‘tough-guy’ image is a misconception
people
Arts and Entertainment
Man of action: Christian Bale stars in Exodus: Gods and Kings
film
Sport
Adnan Januzaj and Gareth Bale
footballManchester United set to loan out Januzaj to make room for Bale - if a move for the Welshman firms up
Arts and Entertainment
British actor Idris Elba is also a DJ and rapper who played Ibiza last summer
filmIdris Elba responds to James Bond rumours on Twitter
PROMOTED VIDEO
Have you tried new the Independent Digital Edition apps?
News
Hackers revealed Oscar-winning actress Lawrence was paid less than her male co-stars in American Hustle
people
Arts and Entertainment
Ellie Levenson’s The Election book demystifies politics for children
bookNew children's book primes the next generation for politics
Sport
Wayne Rooney warms up ahead of the English Premier League football match between Tottenham Hotspur and Manchester United at White Hart Lane
football
News
Outspoken: Alexander Fury, John Rentoul, Ellen E Jones and Katy Guest
newsFrom the Scottish referendum to the Ice Bucket Challenge, our writers voice their opinions
Arts and Entertainment
Lena Headey as Cersei Lannister in Game of Thrones
film
News
i100
Sport
Yaya Sanogo, Mats Hummels, Troy Deeney and Adnan Januzaj
footballMost Premier League sides are after a striker, but here's a full run down of the ins and outs that could happen over the next month
News
Nigel Farage celebrates with a pint after early local election results in the Hoy and Helmet pub in South Benfleet in Essex
peopleHe has shaped British politics 'for good or ill'
Voices
Strictly Come Dancing was watched by 6.9m viewers
voicesIt has been hard to form generally accepted cultural standards since the middle of the 19th century – and the disintegration is only going to accelerate, says DJ Taylor
News
Danielle George is both science professor and presenter
people
News
i100
Latest stories from i100
Have you tried new the Independent Digital Edition apps?
iJobs Job Widget
iJobs General

Recruitment Genius: Panel & Cabinet Wireman

£20000 per annum: Recruitment Genius: Panel Wireman required for small electro...

Recruitment Genius: Electronics Test Engineer

£25000 - £27000 per annum: Recruitment Genius: An SME based in East Cheshire, ...

Recruitment Genius: Marketing Assistant

£18000 - £22000 per annum: Recruitment Genius: Do you have previous experience...

Recruitment Genius: Accounts Administrator

£16000 - £18000 per annum: Recruitment Genius: This is an exciting opportunity...

Day In a Page

War with Isis: The West needs more than a White Knight

The West needs more than a White Knight

Despite billions spent on weapons, the US has not been able to counter Isis's gruesome tactics, says Patrick Cockburn
Return to Helmand: Private Davey Graham recalls the day he was shot by the Taliban

'The day I was shot by the Taliban'

Private Davey Graham was shot five times during an ambush in 2007 - it was the first, controversial photograph to show the dangers our soldiers faced in Helmand province
Revealed: the best and worst airlines for delays

Revealed: the best and worst airlines for delays

Many flyers are failing to claim compensation to which they are entitled, a new survey has found
The stories that defined 2014: From the Scottish independence referendum to the Ice Bucket Challenge, our writers voice their opinions

The stories that defined 2014

From the Scottish independence referendum to the Ice Bucket Challenge, our writers voice their opinions
Stoke-on-Trent becomes first British city to be classified as 'disaster resilient' by the United Nations

Disaster looming? Now you know where to head...

Which British city has become the first to be awarded special 'resilience' status by the UN?
Finally, a diet that works: Californian pastor's wildly popular Daniel Plan has seen his congregation greatly reduced

Finally, a diet that works

Californian pastor's wildly popular Daniel Plan has seen his congregation greatly reduced
Say it with... lyrics: The power of song was never greater, according to our internet searches

Say it with... lyrics

The power of song was never greater, according to our internet searches
Professor Danielle George: On a mission to bring back the art of 'thinkering'

The joys of 'thinkering'

Professor Danielle George on why we have to nurture tomorrow's scientists today
Monique Roffey: The author on father figures, the nation's narcissism and New Year reflections

Monique Roffey interview

The author on father figures, the nation's narcissism and New Year reflections
Introducing my anti-heroes of 2014

Introducing my anti-heroes of 2014

Their outrageousness and originality makes the world a bit more interesting, says Ellen E Jones
DJ Taylor: Good taste? It's all a matter of timing...

Good taste? It's all a matter of timing...

It has been hard to form generally accepted cultural standards since the middle of the 19th century – and the disintegration is only going to accelerate, says DJ Taylor
Olivia Jacobs & Ben Caplan: 'Ben thought the play was called 'Christian Love'. It was 'Christie in Love' - about a necrophiliac serial killer'

How we met

Olivia Jacobs and Ben Caplan
Bill Granger recipes: Our chef's breakfasts will revitalise you in time for the New Year

Bill Granger's healthy breakfasts

Our chef's healthy recipes are perfect if you've overindulged during the festive season
Transfer guide: From Arsenal to West Ham - what does your club need in the January transfer window?

Who does your club need in the transfer window?

Most Premier League sides are after a striker, but here's a full run down of the ins and outs that could happen over the next month
The Last Word: From aliens at FA to yak’s milk in the Tour, here’s to 2015

Michael Calvin's Last Word

From aliens at FA to yak’s milk in the Tour, here’s to 2015