Mussel survey reveals alarming degradation of River Thames ecosystem because the Sixties

University of Cambridge scientists replicated a 1964 River Thames survey and located that mussel numbers have declined by nearly 95%, with one species—the depressed river mussel—utterly gone.

The detailed examine measured the change in dimension and variety of all species of mussel in a stretch of the River Thames close to Reading between 1964 and 2020.

The outcomes have been hanging: not solely had native populations severely declined, however the mussels that remained have been a lot smaller for his or her age—reflecting slower development.

Mussels are vital in freshwater ecosystems as a result of they filter the water and take away algae. As filter feeders they’re uncovered to the whole lot within the water, and this makes them a worthwhile indicator of ecosystem well being. Mussel shells additionally present locations for different aquatic species to reside.

“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,” stated Isobel Ollard, a Ph.D. scholar within the University of Cambridge’s Department of Zoology and first creator 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.”

The examine additionally recorded new arrivals: the invasive, non-native zebra mussel, Dreissena polymorpha, and Asian clam, Corbicula fluminea — each absent from the unique 1964 survey—have been current in excessive numbers. The scientists say invasive species most likely hitched a journey on boats as they sailed up the Thames, and established themselves within the river.

The outcomes are published today within the Journal of Animal Ecology.

“This dramatic decline in native mussel populations is very worrying, and we’re not sure what’s driving it,” stated Professor David Aldridge within the University of Cambridge’s Department of Zoology, and senior creator of the report.

He added: “While this might seem like a rather parochial little study of a single site in a single river in the UK, it actually provides an important warning signal about the world’s freshwaters.”

The invasive species might be behind the decline within the native mussel populations: zebra mussels are identified to smother native species to dying. But the scientists say extra work is required to make sure. Other causes might be adjustments in land use alongside the river, or adjustments within the fish populations that mussels rely upon as a part of their life cycle.

Many empty shells of the depressed river mussel, Pseudanodonta complanata, have been discovered within the survey, indicating that the species had been residing at this web site up to now. The depressed river mussel is among the most endangered mussel species within the UK.

The survey discovered that the inhabitants of duck mussels, Anodonta anatina, had decreased to simply 1.1% of 1964 ranges, and the painter’s mussel, Unio pictorum, decreased to three.2%.

The scientists suppose the mussels’ lowered growth rate might mirror the river’s return to a extra ‘pure’ state. Since 1964, ranges of nitrate and phosphate within the river water have fallen attributable to tighter regulation of sewage remedy. A discount in these vitamins would cut back the expansion of algae, limiting the meals accessible to the mussels.

Mussel species are threatened globally. The scientists say that common inhabitants surveys of key species, like this one, are important to monitoring the well being of rivers and guiding their administration.

To make sure the survey was an exact replica of the unique, Ollard contacted Christina Negus—who had accomplished her survey whereas a researcher on the University of Reading within the sixties. Negus, who’s now not a scientist, shared particulars of the strategies and tools she had used. Her report, revealed in 1966, continues to be cited extensively as proof of the foremost contribution mussels make to ecosystem functioning in rivers.