The waters off the Danish coast are teeming with oysters. While an invasive species is taking over the beaches, indigenous oysters still thrive in the depths of Limfjord – to the great joy of culinary connoisseurs.
The midday sun hangs low in the sky over the Limfjord, its glittering waters almost the same icy blue as Niels Nielsen’s eyes. A giant of a man, he has been working on ships for 23 years – as a cod fisher on his own boat and also as the captain of a tug laying cables off the coast of Brazil. “But there’s no place for small children in the seaman’s life,” says Nielsen, laughing loud enough to drown out the drone of the boat’s diesel engine. Today, 43-year-old Nielsen lives with his family beside his native Limfjord, a sound covering 1500 square kilometers in northern Denmark. He works here as the skipper of the Egon P, a small, bright-red research boat. “Let’s bring up the treasure, then,” says Nielsen.
The fishing gear emerges from the waves and spills its contents, black and heavy, into the boat’s stern: thousands of blue mussels and dotted among them, plump starfish that evidently live very well off the shellfish. There are no flat fish in the net because “the seals and cormorants grab them,” says Nielsen. Then from among the shellfish, the skipper picks out the true pieces of gold, hard and as large as the palm of his hand – dozens of magnificent specimens of the Limfjord oyster, the most exclusive item on the Nordic menu. A single one of these oysters can cost as much as eight euros at restaurants in Copenhagen. Pacific oysters farmed in aquaculture account for 94 percent of all oysters consumed worldwide; the European oyster’s share of the global oyster market is a tiny 0.2 percent. Among these exceptions, the Limfjord oyster is actually a special case because the European oyster isn’t farmed here; the fishermen take only wild specimens from the bed of the shallow sound.
There used to be oyster fishing grounds off the coast of Sylt and other North Sea islands, but overfishing long ago decimated stocks, making the European oyster extinct in the German Wadden Sea. That won’t be happening in the Limfjord, though, as Nielsen and his colleagues from the Danish Shellfish Centre at the Technical University of Denmark (DTU) monitor the vulnerable oyster population by making test catches that provide the basis on which the fishing quotas are set. In 2018, only 300 tons of oysters were brought up, roughly ten percent of the estimated total quantity. Until now, only one out of 100 Limfjord oysters have been consumed in Denmark. Most of the catch is flown to Galicia, to Madrid and Barcelona, where restaurants impatiently await their arrival. For a long time, the Danes were not known for their gourmet palates, but rather as a nation of traders, who loved their fried bacon. But that’s all changed thanks to New Nordic Cuisine. Started by top chefs like René Redzepi of the Noma restaurant in Copenhagen, that trend is now making its way into hinterland kitchens. Everywhere the emphasis is now on regional and seasonal ingredients, kelp from the coast, for example, and sea buckthorn form the dunes. The European oyster barely survives further north than the Limfjord. Redzepi cites the low water temperature as the reason for their being the world’s best: the colder the water, the slower the oysters’ growth and the more intense their flavor.
Nielsen places an oyster in a folded tea towel. This will protect him should his knife slip. With a practiced hand, he slits the tough adductor muscle and removes the top half of the shell to reveal the mollusk in its mother-of-pearl bed. A few drops of lime juice and I slurp it down raw. Fantastic!
The daily life of an oyster is pretty monotonous. It sits in one spot and pumps water through its gills, filtering out the microorganisms that form its diet. You could also say that it spends its life concentrating the taste of the sea. Limfjord oysters feel surprisingly meaty on the tongue. Novices have to steel themselves the first time they shuck an oyster out of the bottom half of its shell and put it straight in their mouth, even if it is a well-known fact that the brainless mollusk feels nothing. For Erwin Lauterbach, chef at the Lumskebugten restaurant in Copenhagen, it’s the same as with other sophisticated tastes: practice intensifies the experience. “No one enjoys their first oyster,” says Lauterbach, “it’s an acquired taste.” An oyster need not even play the aromatic lead in a dish, it even unleashes its magic when concealed, in the form of a few chopped oysters mixed into ox tartare, for instance: “Then you find yourself wondering about a certain saltiness that lends something amazingly unexpected, a lightness, to a recipe.” A daily dish might be creamed potatoes with two or three oysters as a side, “simple and festive at the same time – that’s oysters for you.”
Klaus Louring likes them best the way they were eaten in the Stone Age. Before we try Stone Age preparation, we first have to become hunters and gatherers ourselves, on the island of Fanø in the Danish Wadden Sea. Louring, 55, was a seaman in his youth and worked on container ships sailing between Europe and Asia. Now he’s a coastal ranger on Fanø, where he initiates school classes and tourists in the mysteries of the Wadden Sea. At low tide, he leads his listeners out to the young Pacific oyster beds. Since the 1990s, walkers on the mudflats have been able to observe how this particularly invasive species has been establishing itself and spreading in the shallow waters along the Danish coast. The Pacific oyster has a hard, elongated shell with sharp edges. These wild oysters are almost certainly the offspring of oysters cultivated in the many aquaculture operations around the North Sea: Eggs are fertilized by semen in the water, and then the current carries the larvae a long way off. No one can control where the oysters come to rest. “In the Wadden Sea, the Pacific oyster has only one enemy,” says Louring, as we find the first few in the mud, “homo sapiens with his excellent appetite.”
So far, there has been no specific research into this invasive species’ potential impact on the Wadden Sea. It is unlikely to affect the European oyster, which grows at depths of up to 30 meters, but it does seem likely that it could displace indigenous species, such as the blue mussels. “In some places, both the mussel populations and individual specimens are becoming smaller,” says Louring. It could have something to do with the fact that oysters, like mussels, are dependent on the microorganisms that the tides wash into their gills. “An oyster filters 12 liters of water an hour,” Louring points out, while a mussel manages only six liters at most. Fewer mussels would mean trouble for the millions of migrating birds that replenish their energy reserves in the Wadden Sea before continuing their flight south. The birds can crack open a mussel, but not an oyster. “The more we take, the better,” says Louring.
We walk almost two kilometers out onto the mudflats, past “spaghetti factories,” as Louring calls the tiny piles lugworms leave behind on the mud. Lawyer Snorre Kehler is holding his little daughter Viktoria’s hand. Their pail soon fills up with the fresh shellfish, many of them big as a man’s fist. “We want to cook a Mediterranean-style meal with them back at our holiday home,” says Kehler’s wife, Natasha, an IT consultant, “we’ll bake them in the oven with a little parmesan cheese, parsley and garlic on top – they taste best that way.” But we also sampled a few right there on the beach, where our guide lit a campfire. “In the Stone Age, they only had knives made of flint, and you can’t open an oyster with one of those,” says Louring, laying a few oysters into the embers. After a few minutes on the fire, the liquid inside the oyster begins to boil and expand and – the shells plop open.
The people of Ertebølle on the Limfjord were already tucking into European oysters 7400 years ago, as we know from a gigantic pile of oyster shells discovered by archeologists along what was once the coastline. The pile is 140 meters long, 20 meters wide and two meters high, an accumulation of the oyster shells Stone Age people gathered and split open over their beach fires over a period of 1500 years. Among the shells, the archeologists also found fish bones and pottery shards with traces of burned-on bouillabaisse still clinging to them. The remains of human skeletons were also discovered in the stack. An examination of the bones revealed that the people of that time were healthier than their descendants, who became farmers and lived off cereals and the animals they kept.
Just how many Limfjord oysters there will be in the future also depends on their reproduction strategy. A stay-at-home that holes itself up behind the hardest calcium carbonate needs to be creative if it wants to reproduce: Oysters change their gender. Most of the time, the Limfjord oysters are male, says Lene Friis Møller, a marine biologist at the DTU’s Danish Shellfish Center, “and they only become female and produce eggs in fine weather summers, when the water temperature remains above 18 degrees over a longer period, and there are ample supplies of plankton in the water.” In 2018, Denmark enjoyed an exceptionally long, warm summer – ideal conditions for oyster offspring. It takes a Limfjord oyster three years to grow to 100 grams – serving size. It seems good times lie ahead for fans of the world’s best oysters.