Mussels, the hardworking cleaners of river waters, need help from researchers

The rehabilitation and culturing of freshwater pearl mussels is necessary in order to save this hardworking cleaner of river waters from extinction.

So says Professor Jouni Taskinen, director of Konnevesi Research Station, who has a long research career focused on the mussel. Taskinen has studied protection biology on freshwater pearl mussels for 15 years already. He found his way into this topic when doing his doctoral dissertation, where he studied parasites of mussels.

Researchers know of 150 freshwater pearl mussel populations in Finland. However, the mussel’s reproduction rate is sustainable in 10 to 15 rivers only. This makes the species severely endangered.

The situation has deteriorated especially fast over the past couple of decades, says Taskinen.

The freshwater pearl mussel has suffered for many reasons. Many traditional mussel rivers have been dammed, preventing the migration of salmon upstream, which is crucial for the mussel’s reproduction cycle. Another harm for the mussels is the siltation of river and brook waters: juvenile freshwater pearl mussels can cope in gravel-bedded waters only, where clear and oxygen-rich water penetrates deep into the gravel bed.

In Konnevesi, researchers rehabilitate and deliver juvenile mussels to their natural habitats

The efforts to save freshwater pearl mussels began at the University of Jyväskylä’s Konnevesi Research Station in 2016, when the first batch of 100-year-old individual mussels in poor condition were transferred from the Mustio and Ähtävä Rivers to the station’s nursery pools for revival.

The pools provide favourable conditions for mussels: The oxygen level and flow of water as well as the available amount of algae are kept optimal.

Thus far, freshwater pearl mussels have been brought to Konnevesi from twelve rivers from different parts of Finland. The number of new mussel offspring produced in the nursery pools varies annually – at best, it is more than a hundred thousand per year.

Juvenile mussels are not usually returned to their home rivers right away as “newborns”. 

Their further nursing is not easy, but thousands of juveniles can be planted to nature each year", Taskinen explains.

The first juvenile mussels were transferred from Konnevesi to their home river in summer 2021. How have the returns succeeded so far?

“Because their size is just one or two millimetres and the juveniles burrow deep into gravel for several years, they are hard to observe before they have grown and emerged,” says Taskinen. 

The survival rate of juveniles placed in gravel boxes on the riverbed has ranged from zero up to 90 percent.”

Taskinen is quick to point out, however, that with freshwater pearl mussels, everything happens very slowly.

“How many juveniles actually reach the age of fertility, around 15 to 20 years? With this species, everything happens so slowly that the eventual outcomes can be found out only after a number of years.”