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Mussels in River Thames being wiped out

As filter feeders mussels are exposed to everything in the water. Their shells also provide places for other aquatic species to live.

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By Mark Waghorn via SWNS

Native mussels in the River Thames are being wiped out and invasive species could be to blame, according to alarming new research.

Ironically their disappearance could also be down to cleaner water depriving them of the algae that they feed on.

The shellfish are vital for maintaining aquatic ecosystems by filter feeding.

First author Isobel Ollard, a zoologist at the University of Cambridge, said: "Mussels are a great indicator of the health of a river.

"Such a massive decline in mussel biomass is also likely to have a knock-on effect for other species, reducing the overall biodiversity."

Numbers have declined by almost 95 percent with one type - the depressed river mussel - completely gone.

Ollard, a PhD student, said: "It 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 Thames is renowned across the globe. It was key to Britain ruling the waves - and London becoming the capital city of world finance.

Ollard's team tracked the change in size and number of all mussel species in a stretch near Reading between 1964 and 2020.

Results were striking. Native populations severely declined and those that remained were much smaller - reflecting slower growth.

As filter feeders mussels are exposed to everything in the water. Their shells also provide places for other aquatic species to live.

The study also recorded high numbers of new arrivals - including the non native zebra mussel and the Asian clam.

They were both absent from an original 1964 Port of London Authority survey which the zoologists replicated.

Invasive species could be behind the phenomenon. Zebra mussels are known to smother natives to death.

It is believed they hitched a ride on boats - sailing up the river and establishing themselves.

Senior author Professor David Aldridge said: "This dramatic decline in native mussel populations is very worrying, and we are not sure what is driving it.

"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."

Other causes could be changes in land use along the river, or changes in fish populations that mussels depend on as part of their life cycle.

The Thames has the most microplastics of any river in the world. Around 200 tons are pulled from it every year.

Many empty shells of the depressed river mussel were found - showing the species had been living at the site in the past. It is one of the most endangered in the UK.

Duck mussels had plunged to just 1.1 percent of 1964 levels, and the painter’s mussel to only 3.2 percent.

Reduced growth rate may reflect the river's return to a more 'natural' state. Levels of nitrate and phosphate have fallen due to tighter regulation of sewage treatment. Algae depend on the nutrients, limiting the mussels' food.

Mussels are threatened globally. The scientists called for regular population surveys of key species to track the health of rivers and guide their management.

The Thames is the longest river in England. For over 2,000 years, it has played a central role in British history.

It enabled the Romans to establish London as a settlement in 43 AD. The study is in the Journal of Animal Ecology.

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