Freshwater pearl mussels – the historians of the river
The SALMUS project (Salmonid Fish and Freshwater Pearl Mussel – Ecosystem Services and Biodiversity in the Green Belt of Fennoscandia) is a monitoring project of the endangered freshwater pearl mussel (Margaritifera margaritifera) and their host species, the brown trout and Atlantic salmon in different streams of this region. It is an international collaborative project of Russia, Finland, Sweden, and Norway funded by KOLARTIC Cross Border Cooperation. I joined in the project for the fieldwork and was stung by mosquitos of many different rivers.
The freshwater pearl mussel (have a look at this video to see some mussels: https://wwf.fi/en/wildlive/freshwater-pearl-mussel/) has a special lifecycle that is connected to the appearance of trout or salmon: The larva (which are smaller than one centimetre) are released in the late summer into the water from an adult mussel and needs to find a suitable host – for example the brown trout. Most of the tiny mussels are swept away never to be seen again, but those that are inhaled by a trout, close their shells, hold onto the gills of the fish and live as parasites from their blood cycle. When the water gets warmer in the next spring, the (now a little larger) mussels let go of the gills and let themselves sink to the bottom and bury themselves into the sandy ground. They grow very slowly and, depending on the environmental circumstances, they can get 40-300 years old! In this slightly colder northern region with oligotroph surroundings they reach around 200 years. During this timeframe, the area was ruled by Norwegian, Finish, and shortly also German governments while all the mussels were filtrating tirelessly in the creeks. While growing all this time, the mussels create growth rings in their shells as we know it from the inside of trees. These rings may be used to determine ecological conditions back in time and detect if there were big changes in the period when the mussel lived.
While being in the field, we found many mussels of different size and age ranges. The range was from under two centimetres (under 10 years old) up to more than 13 centimetres (about 200 years old)! I thought that one specific creek was very astonishing: it flows through a meadowlike fen with a width of only about half a metre and in one day we were able to find more than 10,000 freshwater pearl mussels living there!
The freshwater pearl mussel is a key species in river ecosystems because they filtrate the water and provide nutrients for other species. Together with the connected salmonid fishes, they are indicators of ecosystem functions and health. With this project, the status of streams and rivers can be determined and in addition, the freshwater pearl mussels are monitored.
I’m very glad that I have been able to get an insight on so many different projects in the short time period that I have been staying north of the northern polar circle. All this research leads to more knowledge about the different ecosystems, our environment and the climate change that affects everyone but will probably change the Arctic region the most (for more information go to the station’s website: http://www.svanhovd-molecol.no). Luckily, I may come back next summer to write my master’s thesis and gain an even closer insight in this unique region.