A mussel gathered in the new River Thames survey. Credit: University of Cambridge
Key Points:
- When researchers replicated a 1964 River Thames survey, they found significantly decreased numbers of mussels.
- One species was completely gone, while others were severely declined and smaller for their age, reflecting slower growth.
- Mussels are essential to tracking the health of rivers and guiding their management.
Scientists in the UK replicated a 1964 River Thames survey and found that mussel numbers have declined by almost 95%, with one species completely gone.
While the depressed river mussel used to be widespread in the Thames, the current survey did not find a single one. It did, however, record new arrivals: the invasive, non-native zebra mussel Dreissena polymorpha, and Asian clam Corbicula fluminea—both absent from the original 1964 survey but now present in high numbers.
The scientists say the invasive species probably hitched a ride on boats as they sailed up the Thames, and established themselves in the river.
The invasive species could be behind the decline in the native mussel populations as zebra mussels are known to smother native species to death. But the team says more work is needed to be sure. Other causes could be changes in land use along the river, or changes in the fish populations that mussels depend on as part of their life cycle.
According to the study, published in Journal of Animal Ecology, the researchers did find empty shells of the depressed river mussel, Pseudanodonta complanata, indicating the species had been living at the site in the past. The depressed river mussel is one of the most endangered mussel species in the UK.
The survey also found that the population of duck mussels, Anodonta anatina, had decreased to just 1.1% of 1964 levels, and the painter’s mussel, Unio pictorum, decreased to 3.2%.
The scientists think the mussels’ reduced growth rate may reflect the river’s return to a more “natural” state. Since 1964, levels of nitrate and phosphate in the river water have fallen due to tighter regulation of sewage treatment. A reduction in these nutrients would reduce the growth of algae, limiting the food available to the mussels.
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.
Information provided by University of Cambridge.