Natural construction side / The pearl mussel

Pearl mussel, a remarkable specie

This mussel can produce a pearl on the inside of his shell, for example after intrusion of a sand grain. To protect herself against this foreign particle, she envelops it with nacre in spherical layers. Only 1 mussel of 1000 produces a pearl.

But mussel's real treasure lies in his life cycle. It's because of this cycle the mussel is so vulnerable. Every stage has his own milieu requirements (water quality, quantity of food,...). Due to this fragility she's a so-called umbrella species since the renaturation of his habitat is also good for plenty other species (fish,...).

The mussel's life cycle contains four stages: larval , parasitic , juvenile and adult stage.

In the juvenile stage the mussel, now capable to filtrate water, ascends to the limit between free water and sediment. It takes another 10 years 'till his sexual maturation. His life expectancy is between 100 years in our region and 150 in the north of Europe!	At the end of summer, thousands of larvae are liberated in the water course. To survive, they have to anchor thereselves for 10 month on the gills of a host fish (brown trout). Without trout, no pearl mussel!	In spring, the larva breaks away from the fish and sinks on the river ground . She buries herself into the sediment to stay there for 5 years..

An exigent species

The pearls massel's life milieu is characterised by rivers close to the natural state, poor in nutriments (nitrate, phosphate), cold in summer and riche in oxygen. The water quality has to be excellent.

The borders of water courses has to be humid zones to assure the nutrition resources (organic particles from decomposition of vegetation) and bonds of trees on river banks assure the cold temperatures in summer.

The congestion of sand and gravel sediment caused by earth ripple on the river ground is a big problem for the larvae burying themselves into the ground. It provokes an oxygen deficiency witch implicates death of the juveniles.

LIFE CYCLE OF PEARL MUSSEL