The freshwater mussels that live in the Thames have been declining in number since the 1960s. (Envato Elements pic)
PARIS: The freshwater mussels that live in the Thames are becoming less and less numerous.
A team of researchers from the University of Cambridge has studied the evolution of these mollusks in the famous English river from 1964 until 2020, in a section near Reading. And according to their findings, the mussels in this part of the Thames appear to have been in continual decline since that time.
The study, published in the Journal of Animal Ecology, reports the total disappearance of certain species of mussels.
This is notably the case of the depressed river mussel (Pseudanodonta complanata), classified as a “threatened species” on the International Union for Conservation of Nature’s red list.
Most of the freshwater mussel species found in this part of the Thames have also experienced a decrease in their growth rate compared to 1964, the scientists report.
According to the study, this phenomenon can be explained by several factors, such as the proliferation of invasive species (such as non-native bivalves), but also water pollution that modifies the nutrient supply of mussels as well as changes to their habitat linked to climate change.
And the decline of freshwater mussels is not without consequences on river ecosystems.
Isobel Ollard, a PhD student at the University of Cambridge’s department of zoology and first author of a paper, told The Guardian that an adult mussel can filter up to 40 litres of water a day, thus removing significant amounts of algae and contributing to keeping rivers clean.
“Such changes are likely to have significant impacts on other freshwater species and broader ecosystem functioning,” the study states.
Since the research was conducted at just one site, the authors stress the need to broaden the scope of the research to other areas of the Thames, as well as other freshwater sites in Europe, to learn more about the reasons for this decline.
“This study demonstrates the vital importance of maintaining up-to-date knowledge about wild populations, including for species not currently classed as threatened,” conclude the researchers.
