̽��ֱ�� of Cambridge - mussel

Meet Cambridge's mussel man

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How new ways of shellfish farming could help meet future food needs.

Mussel memory

cg605 — Mon, 28 Nov 2022 10:02:49 +0000

How fresh-water mussels and a stretch of the River Thames connected two postgraduate scientists separated by over half a century.

Mussel survey reveals alarming degradation of River Thames ecosystem since the 1960s

jg533 — Mon, 28 Nov 2022 09:27:25 +0000

̽��ֱ��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.

̽��ֱ��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 ̽��ֱ�� of Cambridge’s Department of Zoology and first author of the report.

She added: “ ̽��ֱ��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.”

̽��ֱ��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. ̽��ֱ��scientists say invasive species probably hitched a ride on boats as they sailed up the Thames, and established themselves in the river.

̽��ֱ��results are published 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 ̽��ֱ�� 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.”

̽��ֱ��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. ̽��ֱ��depressed river mussel is one of the most endangered mussel species in the UK.

̽��ֱ��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%.

̽��ֱ��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. ̽��ֱ��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 ̽��ֱ�� 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.

̽��ֱ��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 it

David Aldridge

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Britain on brink of freshwater species ‘invasion’ from south east Europe

fpjl2 — Mon, 13 Oct 2014 09:42:10 +0000

Five of the most high-risk freshwater invaders from the Ponto-Caspian region around Turkey and Ukraine are now in Britain - including the quagga mussel, confirmed just two weeks ago on 1 October in the Wraysbury River near Heathrow airport.

Researchers say that, with at least ten more of these high-risk species established just across the channel in Dutch ports, Britain could be on the brink of what they describe as an ‘invasional meltdown’: as positive interactions between invading species cause booming populations that colonise ecosystems - with devastating consequences for native species.

̽��ֱ��authors of a study on 23 high-risk invasive species, published in the Journal of Applied Ecology, describe Britain’s need to confront the Ponto-Caspian problem - named for the invaders’ homelands of the Black, Azov and Caspian seas - as a 'vital element for national biosecurity'.

They say monitoring efforts should be focused on areas at most risk of multiple invasions: the lower reaches of the Rivers Great Ouse, Thames and Severn and the Broadlands, where shipping ballast water and ornamental plant trading is most likely to inadvertently deposit the cross-channel invaders.

All of these areas are projected to see an influx of up to twenty Ponto-Caspian invading species in the near future.

“Pretty much everything in our rivers and lakes is directly or indirectly vulnerable,” said Dr David Aldridge, co-author from the ̽��ֱ�� of Cambridge’s Department of Zoology, who confirmed the quagga find.

“ ̽��ֱ��invader we are most concerned about is the quagga mussel, which alarmingly was first discovered in the UK just two weeks ago. This pest will smother and kill our native mussels, block water pipes and foul boat hulls. We are also really worried about Ponto-Caspian shrimps, which will eat our native shrimps.”

̽��ֱ��most aggressive invasive shrimp have ominous monikers: the demon shrimp, bloody red shrimp and the notorious killer shrimp - dubbed the ‘pink peril’.

These organisms have already been recorded in Britain, and experts warn they will act as a gateway for further species due to favourable inter-species interactions that facilitate invasion, such as food provision and ‘commensalism’ - in which one species obtains benefits from another’s place in an ecosystem.

̽��ֱ��researchers point to the example of the zebra mussel, a Ponto-Caspian outrider and relation of the quagga first seen in the UK in 1824 and now widespread. Zebra and quagga mussels smother Britain’s native mussels, preventing them from feeding and moving. ̽��ֱ��invading mussels also provide an ideal home for Ponto-Caspian amphipods such as killer and demon shrimps, which have striped patterns to blend in with the mussels’ shells.

These amphipods, in turn, provide food for larger invaders such as goby fish. Ponto-Caspian gobies have now made their way down the Rhine, one of the main “corridors” to Britain, with populations exploding in the waterways of western France over the last few years. ̽��ֱ��invading gobies eat native invertebrate and displace native fish such as the already threatened Bullhead.

Once the Ponto-Caspian species reach coastal areas of ̽��ֱ��Netherlands, they are transported across the channel in ballast water taken on by cargo ships, or hidden in exported ornamental plants and aquatic equipment such as fishing gear.

“If we look at ̽��ֱ��Netherlands nowadays it is sometimes hard to find a non-Ponto-Caspian species in their waterways,” said Aldridge.

“In some parts of Britain the freshwater community already looks more like the Caspian Sea. ̽��ֱ��Norfolk Broads, for example, typically viewed as a wildlife haven, is actually dominated by Ponto-Caspian zebra mussels and killer shrimps in many places.”

“Invasive species – such as the quagga mussel – cost the UK economy in excess of £1.8 billion every year,” said Sarah Chare, deputy director of fisheries and biodiversity at the UK Environment Agency.

“ ̽��ֱ��quagga mussel is a highly invasive non-native species, affecting water quality and clogging up pipes. If you spot one then please report it to us through the online recording form.”

Through an in-depth analysis of all reported field and experimental interactions between the 23 most high-risk invasive Ponto-Caspian species, the researchers were able to identify 157 different effects - the majority of which enabled positive reinforcement between species (71) or made no difference (64).

Dates and locations of the first British reports of 48 other freshwater invaders from around the world show that 33% emerged in the Thames river basin, making it the UK hot spot for invaders, followed by Anglian water networks (19%) and the Humber (15%).

̽��ֱ��time between a Ponto-Caspian species being reported in ̽��ֱ��Netherlands and Britain has shrunk considerably - from an average of 30 years at the beginning of the 20th century to just 5 in the last decade.

“Due to globalisation and increased travel and freight transport, the rate of colonisation of invasive species into Britain from ̽��ֱ��Netherlands keeps accelerating - posing a serious threat to the conservation of British aquatic ecosystems,” said co-author Dr Belinda Gallardo, now based at the Doñana Biological Station in Spain.

“Cross-country sharing of information on the status and impacts of invasive species is fundamental to early detection, so that risks can be rapidly assessed. A continuing process for evaluating invasive species and detecting new introductions needs to be established, as this problem is increasing dramatically.”

Inset image: 'Killer' shrimp by Thomas Smith/Environment Agency

New research shows multiple invasive species with the same origin facilitate each other’s ability to colonise ecosystems. By studying how these species interact as well as current population locations, researchers believe that Britain is heading for an ‘invasion meltdown’ of freshwater species from south east Europe.

Pretty much everything in our rivers and lakes is directly or indirectly vulnerable

David Aldridge

David Aldridge/Thomas Smith via Environment Agency

Top: quagga mussel hitching a ride on a zebra mussel. Bottom: killer shrimp

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