A zoology student has made a ‘very worrying’ discovering about declining biodiversity in the River Thames in Reading.

Cambridge PhD scholar Isobel Ollard found the mussel population has been almost completely wiped out in the six decades since Reading zoologist Tina Negus surveyed the same stretch of river in 1964.

Mussels are an important indicator of the health of a river ecosystem and such a large decline in biomass is likely to have a knock-on effect for other species.

Isobel said: “This key piece of information has proved really significant in revealing how ecological conditions have changed at this site near Reading, and it acts as a clear warning signal about threats to the world’s freshwaters.

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“Tina’s important research from almost six decades ago was vital in helping us to understand the health of the Thames today.”

Mussel numbers have declined by around 95 per cent, with one species – the depressed river mussel – almost completely gone.

The mussels that remained were much smaller for their age, reflecting slower growth.

These findings were described as “very worrying” by Isobel, as mussels help to filter water, remove algae, and provide places for other aquatic species to live.

Tina, aged 80, said: “In the past 60 odd years, there's been quite a difference. It must be fairly unusual to have a project start at the same place on the same topic so many years apart where the original researcher is still alive and kicking.

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“Despite the results, it was nice to know that it was being carried out using identical techniques after all this time. Maybe in another 50 years, somebody else will carry out the survey in the same area.”

Tina’s childhood interest in natural history led to her choosing to study zoology, botany and geography as an undergraduate at the University of Reading in the 1950s.

She then had the opportunity to do a postgraduate degree, including research on freshwater mussels on the River Thames.