This February, we shine the spotlight on the freshwater pearl mussel (Margaritifera margaritifera)—a species assessed in our project as Endangered (EN), facing a very high risk of extinction in the wild.

How can you recognize the species?

The mussel is enclosed by two symmetrical shell valves, which protect its soft body and a skin-like organ called the mantle. At the rear end of the body, the mantle forms the inhalant and exhalant siphons. The mantle secretes material that gradually builds up the thick shell.

The two shell halves are held together by a flexible ligament. The right valve has one cardinal tooth, while the left has two. Juvenile mussels have thin, yellow-brown shells, whereas adults have dark or completely black shells, often showing signs of wear, encrustation, or sediment deposits. The visible growth rings on the shell surface can help estimate the mussel's age.

If a foreign object—such as a grain of sand, a parasite, or damaged mantle tissue—gets trapped between the shell and the mantle, the mussel gradually covers it with thick concentric layers of nacre (mother-of-pearl), forming a pearl. In Latvia, pearls were historically harvested over a long period. However, since the mid-19th century, various sources have noted that pearls could no longer be collected due to overharvesting.

In Latvia, the species is threatened by habitat loss and water pollution. The main risk is juvenile mortality in the first few years of life, as the young are extremely sensitive to elevated nitrogen levels in the water. The species also suffers from changes in river hydrology and flow, including obstacles like hydropower plants, beaver dams, as well as riverbed and bank alterations and drainage system installations. In dammed areas, sediment levels and water temperatures rise, while oxygen levels drop. Pearl mussels can also perish during droughts when streams dry out.