Photo Credit: Gil Ndjouwou |
The detailed study measured the change in size and number of all species of mussel in a stretch of the River Thames near Reading between 1964 and 2020.
The results were striking: not only had native populations severely declined, but the mussels that remained were much smaller for their age – reflecting slower growth.
Mussels are important in freshwater ecosystems because they filter the water and remove algae. As filter feeders they’re exposed to everything in the water, and this makes them a valuable indicator of ecosystem health. Mussel shells also provide places for other aquatic species to live.
“Mussels are a great indicator of the health of the river ecosystem. Such a massive decline in mussel biomass in the river is also likely to have a knock-on effect for other species, reducing the overall biodiversity,” said Isobel Ollard, a PhD student in the University of Cambridge’s Department of Zoology and first author of the report.
She added: “The depressed river mussel used to be quite widespread in the Thames, but this survey didn’t find a single one - which also raises concerns for the survival of this species.”