Mighty mussels make for healthier rivers

  • 12 May 2025
  • 2 minute read
  • Words Natasha Wiseman
Freshwater pearl mussels like this one can filter water and slow the flow. Image: Raviv Gal.

Freshwater pearl mussels are one of nature's less-recognised ecosystems engineers, according to a researcher at Karlstad University in Sweden, but by filtering water, slowing down the flow and producing nutrient-rich faeces, they affect the entirety of a watercourse's life.

Freshwater pearl mussels are one of Sweden's longest-living animals – with some individuals having lifespans of 280 years. Raviv Gal examined how the bivalve molluscs affect the decomposition of leaves, insect life and fish behaviour.

"We need to protect them, not just for the sake of the species, but also to preserve the entire ecosystem's function."

Raviv Gal, Karlstadt University

"They may look a bit like stones and don't move much, but they have a significant impact on their surroundings," says Raviv Gal, who recently defended his PhD in biology at Karlstad University. "They do so much more than you think."

The results were surprising. Gal found that the presence of the mussels in rivers and streams contributes to:

  • Slower decomposition of leaves – possibly because insects prefer to eat mussels' faeces over plant parts, or because the mussels protect the leaves from the flow
  • Less dominance of gnats – which benefits the diversity among bottom-dwelling animals
  • Better conditions for small trout, which find it easier to swim in fast flows where mussel populations are present
Raviv Gal undertook his doctoral research at Karlstadt University

"Mussels should probably become really popular among those who don't like gnats!" says Raviv, laughing.

Populations of freshwater pearl mussels have drastically decreased in Europe, with up to 80% having disappeared in the last 90 years. Today, many of the remaining populations are found in Sweden and Norway.

"This makes us responsible," says Gal, who hopes his research will contribute to healthier watercourses and increased biodiversity. "We need to protect them, not just for the sake of the species, but also to preserve the entire ecosystem's function."

Freshwater mussels at work in a stream. Image Raviv Gal

Fewer blackflies, higher biodiversity, and slower decomposition – these are some of the unexpected effects that freshwater pearl mussels have on their surroundings in the stream.

"It feels incredible to have been able to contribute to the knowledge about these animals, and the research doesn't end here," says Gal, whose next research project is on damselflies.