Discovery of world’s oldest DNA breaks record by one million years.

The Entrepreneurship Centre at Cambridge Judge Business School is supporting new ventures to improve sustainability in agriculture to meet the demands of a growing global population.  

The Entrepreneurship Centre at Cambridge Judge Business School is supporting new ventures to improve sustainability in agriculture to meet the demands of a growing global population.  

The detailed study measured the change in size and number of all species of mussel in a stretch of the River Thames near Reading between 1964 and 2020.

The results were striking: not only had native populations severely declined, but the mussels that remained were much smaller for their age – reflecting slower growth.

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.

“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,” said Isobel Ollard, a PhD student in the University of Cambridge’s Department of Zoology and first author 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 study also recorded new arrivals: the invasive, non-native zebra mussel, Dreissena polymorpha, and Asian clam, Corbicula fluminea - both absent from the original 1964 survey - were present in high numbers. The scientists say invasive species probably hitched a ride on boats as they sailed up the Thames, and established themselves in the river.

The results are published today in the Journal of Animal Ecology.

“This dramatic decline in native mussel populations is very worrying, and we’re not sure what’s driving it,” said Professor David Aldridge in the University of Cambridge’s Department of Zoology, and senior author 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 could be behind the decline in the native mussel populations: zebra mussels are known to smother native species to death. But the scientists say 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.

Many empty shells of the depressed river mussel, Pseudanodonta complanata, were found in the survey, indicating that the species had been living at this site in the past. The depressed river mussel is one of the most endangered mussel species in the UK.

The survey 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.

Mussel species are threatened globally. The scientists say that regular population surveys of key species, like this one, are essential to tracking the health of rivers and guiding their management.

To ensure the survey was an exact replica of the original, Ollard contacted Christina Negus – who had done her survey while a researcher at the University of Reading in the sixties. Negus, who is no longer a scientist, shared details of the methods and equipment she had used. Her report, published in 1966, continues to be cited extensively as evidence of the major contribution mussels make to ecosystem functioning in rivers.

The research was funded by a Whitten studentship, Department of Zoology, Cambridge.

Reference

Ollard, I., & Aldridge, D.C. ‘Declines in freshwater mussel density, size and productivity in the River Thames over the past half century.’ Journal of Animal Ecology, November 2022. DOI: 10.17863/CAM.80071

Scientists replicated a 1964 River Thames survey and found that mussel numbers have declined by almost 95%, with one species – the depressed river mussel – completely gone.

This dramatic decline in native mussel populations is very worrying, and we’re not sure what’s driving itDavid Aldridge

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Yes

Cambridge researchers have made the first ever measurements that show rhinoceros horns have gradually decreased in size over time.

A study has found that pheasants killed by lead shot contain many fragments of lead too small to detect by eye or touch, and too distant from the shot to be removed without throwing away a large proportion of otherwise useable meat.

Lead fragments often form when lead shotgun pellets hit the bodies of gamebirds. The fragments become lodged deep within the meat.

Researchers examined the carcasses of eight wild-shot common pheasants, killed on a farmland shoot using lead shotgun ammunition and on sale in a UK butcher’s shop. They found small lead fragments embedded in every pheasant, in addition to lead shotgun pellets in seven of them.

The researchers found up to 10mg of tiny lead shards per pheasant, all of which were much too small to be detected by eye or by touch.

Lead is toxic to humans when absorbed by the body – there is no known safe level of exposure. Lead accumulates in the body over time and can cause long-term harm, including increased risk of cardiovascular disease and kidney damage in adults. It is known to lower IQ in young children, and affect the neurological development of unborn babies.

“While lead gunshot continues to be used for hunting, people who eat pheasants and other similar gamebirds are very likely to be also consuming a lot of tiny lead fragments,” said Professor Rhys Green in the University of Cambridge’s Department of Zoology, and first author of the study.

An earlier study in rats showed that when consumed, more lead is absorbed into the body from smaller fragments than from larger ones.

“It seems to have been widely assumed in the past that a lead shot embedded in a pheasant carcass remained intact, and could be removed cleanly before the pheasant was eaten – removing any health risk. Our study has shown the extent to which this is really not the case,” said Green.

He added: “By eating pheasant, people are also unwittingly eating lead, which is toxic.”

“One pheasant is a reasonable meal for two or three people. Consuming this much lead occasionally wouldn’t be a great cause for concern – but we know that there are thousands of people in the UK who eat game meat, often pheasant, every week.”

Around 11,000 tonnes of meat from wild-shot gamebirds, mostly pheasant, are eaten in the UK every year. Virtually all pheasants shot in the UK for human consumption are killed using lead shot.

The researchers used a high-resolution CT (computerised tomography) scanner to locate the lead fragments in the pheasant meat in three dimensions, and measure their size and weight. The meat was then dissolved, allowing the larger fragments to be extracted and analysed further to confirm they were lead.

An average of 3.5 lead pellets and 39 lead fragments of less than 1mm wide were detected per pheasant. The smallest fragments were 0.07mm wide – at the limit of resolution for the CT scanner for specimens of this size - and the researchers say it is likely that even smaller fragments were also present.

The lead pieces were widely distributed within the birds’ tissues and some of the small fragments were over 50mm from the nearest lead shot pellet.

The results are published today in the journal PLOS ONE.

“It’s rare for people eating game meat to accidentally eat a whole lead shot, because they’re cautious about damaging their teeth and know to check for lead shotgun pellets in the meat. But the lead fragments we found in pheasant carcasses were so tiny and widely distributed that it’s very unlikely they would be detected and removed,” said Green.

There are no UK or EU regulations about the maximum allowable levels of lead in human food from wild-shot game animals. This is in contrast with strict maximum levels for lead in many other foods including meat from cattle, sheep, pigs and poultry, and shellfish harvested from the wild.

Steel shotgun pellets are a practical alternative to lead, and their use in place of lead for hunting is recommended by UK shooting organisations. But there is very little evidence of a voluntary switch away from lead being made. The UK Health & Safety Executive is currently preparing a case for banning the use of lead ammunition for hunting in the UK, and the European Chemicals Agency is doing the same for Europe.

Other game including partridge, grouse and rabbit is also mainly shot using lead shotgun pellets, and wild deer are shot using lead bullets. Hunters often remove the guts of deer carcasses to make them lighter to carry, and the discarded guts - which often contain many bullet fragments - are eaten by wildlife, which then also suffer the harmful effects of consuming lead.

This research was funded by The Royal Society for the Protection of Birds.

Reference

Green, R.E. et al. ‘Implications for food safety of the size and location of fragments of lead shotgun pellets embedded in hunted carcasses of small game animals intended for human consumption.’ PLOS ONE, August 2022. DOI: 10.1371/journal.pone.0268089

Eating pheasant killed using lead shot is likely to expose consumers to raised levels of lead in their diet, even if the meat is carefully prepared to remove the shotgun pellets and the most damaged tissue.

By eating pheasant, people are also unwittingly eating lead, which is toxic.Professor Rhys Green Robert Trevis-Smith on GettyPheasant

The text in this work is licensed under a Creative Commons Attribution 4.0 International License. Images, including our videos, are Copyright ©University of Cambridge and licensors/contributors as identified.  All rights reserved. We make our image and video content available in a number of ways – as here, on our main website under its Terms and conditions, and on a range of channels including social media that permit your use and sharing of our content under their respective Terms.

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