The oysters in the Wadden Sea

the giant pantry

THE OYSTERS IN THE WADDEN SEA A PROBLEMATIC DELICACY?

Pacific oysters (Crassostrea gigas) are as the Latin species name implies a giant among oysters Pacific oysters are a new species in the Danish Wadden Sea, and a species that presents certain challenges for the ecosystem, albeit one that kindles pleasure for the many food interested tourists.

In 1996, it could be documented for the first time that the Pacific oyster had settled in the Danish Wadden Sea. Over a few years, the number of Pacific oysters rose heavily and resulted in several oyster beds in the Wadden Sea. The oyster beds vary a great deal in size and accessibility, but have become a popular excursion spot for many tourists. With expert knowledge from the tour providers along the Wadden Sea coast, the tourists are escorted out to the oyster beds, where they can freely collect oysters for personal consumption.

Pacific oysters – biology and habitat

Pacific oysters (Crassostrea gigas) are as the Latin species name implies a giant among oysters, where the shell can become up to 40 cm in length. The species can reach an age of 30 and is incredibly hardly since it can tolerate water temperatures ranging from -5C to +40C. It is precisely this tolerance for great fluctuations in temperature that has contributed to its enormous expansion the world over.

Pacific oysters are found near the coasts in Japan, Korea, Siberia, Australia, USA, Canada and Europe.

Experience oysters in ...

SPRING

SUMMER

AUTUMN

WINTER

Algae poisons in oysters During warm periods, the oceans are rife with algae blossoms that are poisonous for human beings. Since oysters feed on the algae in the water, they can very quickly arrive at an infelicitous accumulation of algae poisons, and to such a degree that they will make you very ill if you eat them. Such a poisoning can last from a few days to a few months to even a few years and can cause permanent injury.

It is therefore recommended that private individuals gather and eat oysters ONLY in the colder months from September to April (months with an ”r”). The poison cannot be seen or tasted and is not removed through heating.

Worldwide production Worldwide, more than four million tons of Pacific Oysters are produced per year in various aqua-cultures.

Sten Munk Svendsen, Vadehavscentret & Lasse Fast Jensen, Fiskeri- og Søfartsmuseet Translation: Nanna Mercer, Sirius Translation

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the giant pantry

The Pacific oyster can indirectly displace the food chain balance in the Wadden Sea. Pacific oysters feed by filtering sea water for microscopic plankton algae. Investigations have shown that a Pacific oyster is capable of filtering 12 liters of sea water per hour.

Oysters start life as males, but later change sex to become females - a phenomenon known as ’protandric hermaphrodism’. The females spawn eggs in July and August and can release 20 to 100 million eggs at a time. However, the spawning is not annual in the Wadden Sea since it demands a water temperature of over 20C for a continuous length of time.

From the Pacific ocean to the Wadden Sea

In 1922, the original European oyster (Ostrea edulis) was hit by crayfish plague which, with its high mortality rate wiped out the whole European oyster population in just a few years. In the middle of the 20th century, the shortage of European oysters made it imperative to import Pacific oysters from Japan to Europe. The Pacific oyster was known to be very resistant to the crayfish plague that killed the European oyster population.

The first releases were made in France and Holland during the years 1964 - 1969. A few decades later, in 1986, the Pacific oyster was introduced on the German Wadden Sea island Sylt, with the result that, 10 years later, in 1996, Pacific oysters could be

The French love oysters!

France is the country in Europe that produces the most oysters. In 2004, the production reached 115,000 tons of oysters. The bulk of the French production is consumed in France. Export then, was 7,000 tons of oysters in 2004.

documented in the Danish Wadden Sea. The oyster larvae had moved with the ocean current from Sylt to the Danish Wadden Sea and were thereby introduced as a new species in the Danish environments.

Since Pacific oysters are not native to Danish nature, they are considered an invasive species.

Wadden Sea oysters in the distant past

It has not always been a given that Mr. Everyman had any right to collect oysters in the Wadden Sea. In 1587, Frederik II proclaimed in an open letter that he retained the monopoly to this interesting food from the Wadden Sea. It had become very modern among the European high society to eat oysters; so it was in the King’s interest that oysters from the Wadden Sea be allotted to the throne. Since, naturally, oysters should be available in sufficient numbers for his majesty, the proclamation ended on the

Sten Munk Svendsen, Vadehavscentret & Lasse Fast Jensen, Fiskeri- og Søfartsmuseet Translation: Nanna Mercer, Sirius Translation

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the giant pantry

The oysters banks are a popular destination for many tourists note that the death penalty would befall anyone who was bold enough to collect even one of the oysters that belonged to the King.

Frederik II’s monopoly on oysters lasted until 1676, when the right descended to Hans Schack on Schackenborg castle in Southern Jutland. Thereafter, the right to collect oysters was leased to different merchants.

Pacific oysters today

Today, it is the State in the guise of the National Fisheries Directorate that has the ”right” to issue licenses for commercial fishing of oysters, while the Danish Veterinary and Food Administration supervise the production areas and can open and close for commercial fishing if the incidences of poisonous algae are too high.

The number of Pacific Oysters in the Wadden Sea is huge, and the latest statements from 2008 show that there are approximately 12,000 tons. In addition, the species have spread from the Wadden Sea and up along the Jutlandic west coast to Limfjorden, Horsens fjord, Isefjorden near Kalundborg, and Langeland.

The huge numbers of oysters have created a desire for a new form of tourism - oyster tours. The popular tours take place at the low tide in the Wadden Sea. There is no other place in Denmark where is it possible to stand on solid ground while collecting as many oysters as you can carry.

Pacific oysters – impact on the ecosystem in the Wadden Sea

The many oyster beds in the Wadden Sea function as large reefs that create hiding places for some of the smaller species on the seafloor, such as crabs and starfish. The many hiding places cause an increase in the number of crabs and starfish, which in turn produce an increase in the predation pressure on their respective prey. In this way, the Pacific oyster can indirectly displace the food chain balance in the Wadden Sea. It has also been observed that the Pacific oyster can live on top of already established mussel beds, which reduces the access to the Wadden Sea mussels. This can be significant for the animals that eat mussels such as the eider, the oyster catcher and the herring gull.

Sten Munk Svendsen, Vadehavscentret & Lasse Fast Jensen, Fiskeri- og Søfartsmuseet Translation: Nanna Mercer, Sirius Translation

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the giant pantry

Things to do ...

Learn about oysters here ...

If you want to see and experience the huge beds of Pacific oysters in the Wadden Sea, you can sign up for one of the many public oyster tours with a local provider who knows the way around the wadden.

The Fisheries and Maritime Musuem Tarphagevej 2-6 DK-6710 Esbjerg V. T: +45 76 12 20 00 E: fimus@fimus.dk W: www.fimus.dk

The tours are possible from September to April, when the ocean is coldest and the risk of shell fish poisoning the least.

Vadehavscentret Okholmvej 5 Vester Vedsted DK-6760 Ribe T: +45 75 44 61 61 E: info@vadehavscentret.dk W: www.vadehavscentret.dk Naturcentret Tønnisgård Havnebyvej 30 DK-6792 Rømø T: +45 74 75 52 57 E: info@tonnisgaard.dk W: www.tonnisgaard.dk

tips for further reading

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Migratory birds in the Wadden Sea Life on the Waddens The seals in the Wadden Sea Black Sun

About Vadehavets Formidlerforum...

Vadehavets Formidlerforum is a partnership of visitor centers that mediate the Wadden Sea’s natural and cultural heritage.

VFF’s main activity is to coordinate projects that highlight the nature and culture heritage of the Wadden Sea..

Learn more at www.vadehav.dk

Sten Munk Svendsen, Vadehavscentret & Lasse Fast Jensen, Fiskeri- og Søfartsmuseet Translation: Nanna Mercer, Sirius Translation

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