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The ark for Luxembourg's last freshwater pearl mussels

The ark for Luxembourg's last freshwater pearl mussels

1 3 min. 16.09.2013 From our online archive
Landlocked Luxembourg may be the last place you would expect to find mussels growing in the wild. But, unlike the varieties caught in the sea, the country's freshwater mussels are not destined for the dinner table.
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Landlocked Luxembourg may be the last place you would expect to find mussels growing in the wild. But, unlike the varieties caught in the sea, the country's freshwater mussels are not destined for the dinner table.

Indeed, varieties like the freshwater pearl mussel and thick shelled river mussel are now so rare that a rescue operation is underway in the north of Luxembourg to help revive them through breeding and restoring their habitats.

“We know that there was quite a big population of mussels here. But they're dying out all over central Europe. Most rivers where they used to be they have gone now,” Conservation biologist Frankie Thielen told

Frankie works for the Natur&Emwelt Foundation which has a facility at the Kalborn Mill, near Heinerscheid where the country's last remaining freshwater mussels live.

“This facility is more or less an ark which exists to try to save this local population and other local populations before they are lost forever,” he said.

Frankie explained that the freshwater pearl mussels, which can live up to 80 years, are dying out because their young are being killed off by environmental factors.


The freshwater pearl mussel reproduces by releasing larvae into fresh water which then attach themselves to the gills of host fish, in this case the brown trout. Once the larvae reach a certain size and become “juveniles”, they drop to the river bed where they feed off microscopic algae and organic particles and should grow.

But, a series of factors in Luxembourg are preventing these tiny mussels from surviving into adulthood. Among the main reasons is the sediment being carried by tributaries into waterways. This can happen as a result of changes to the land such as the increased use of concrete in construction and the replacement of deciduous trees with non-native species like the Spruce pine, whose shallow roots do not stabilise the river's banks.

In all cases, water travels down into the valleys carrying sediment, which clogs up the river beds where the mussels grow and feed.

“When you have a flood or the water slows down, creatures in the river protect themselves between the stones and gravel of the river bed. If the water is clean it brings oxygen and food. But if there are too many nutrients and fine sediments it gets clogged and anything living there has problems,” said Frankie, adding: “Other, larger creatures, will find a better spot. But for small mussels, it's hard to move quickly so they die.”

Frankie said that now only around 50 freshwater pearl mussels remain in the area.

Restoring the habitat

The first Life project, which focused on helping the freshwater pearl mussel, has since ended and biological conservationists have now shifted their attention to a new project to protect the thick-shelled river mussel.

In essence though the project continues the work begun to restore the habitat so that all freshwater mussels can continue reproducing unaided. This involves working with landowners to convince them to plant deciduous trees, with farmers to prevent their cattle from churning up the water and generally helping restore water meadows which act as a sponge and regulate the flow of water.

Currently, the European Water Framework Directive demands that all water bodies reach again the good status. The waterway in question is at a good level but for the mussels to survive unaided by humans, the water must be classed “very good”, a change that will not come easily.

“It's very hard. The whole catchment area is 700 square kilometres, which affects the water quality. There are no huge companies or sewerage plants causing problems. It's simply that we have lots of small problems,” said Frankie.

Healthy rivers equal healthy people

But, while the work is challenging, it is worthwhile and not only for the sake of a few mussels. If these mussels are able to reproduce then it shows the river is well managed and that the country's water resources are sustainable.

Furthermore, mussels serve to clean the water, filtering up to 50 litres per day. “It's an ecosystem service they provide for us because the water is eventually used by us, by humans. When you think how much water supplier companies pay to filter water for human consumption. If you've mussels that can help then you won't need these expensive filters,” said Frankie.

To find out more about the project's findings, visit