̽��ֱ�� of Cambridge - Isobel Ollard

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

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. Images, including our videos, are Copyright © ̽��ֱ�� 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.

Yes

Conservationists may be unintentionally spreading pathogens between threatened animal populations

jg533 — Mon, 12 Apr 2021 09:00:42 +0000

̽��ֱ��new report published in the journal Conservation Letters focuses on freshwater mussels, which the researchers have studied extensively, but is applicable to all species moved around for conservation purposes.

Mussels play an important role in cleaning the water of many of the world’s rivers and lakes, but are one of the most threatened animal groups on Earth. There is growing interest in moving mussels to new locations to boost threatened populations, or so they can be used as ‘biological filters’ to improve water quality.

A gonad-eating parasitic worm, Rhipidocotyle campanula, which can leave mussels completely sterile, was identified as a huge risk for captive breeding programmes where mussels from many isolated populations are brought together.

“We need to be much more cautious about moving animals to new places for conservation purposes, because the costs may outweigh the benefits,” said Dr David Aldridge in the Department of Zoology at the ̽��ֱ�� of Cambridge, senior author of the report.

He added: “We’ve seen that mixing different populations of mussels can allow widespread transmission of gonad-eating worms – it only takes one infected mussel to spread this parasite, which in extreme cases can lead to collapse of an entire population.”

Pathogens can easily be transferred between locations when mussels are moved. In extreme cases, the pathogens may cause a population of mussels to completely collapse. In other cases infections may not cause a problem unless they are present when other factors, such as lack of food or high temperatures, put a population under stress leading to a sudden outbreak.

̽��ֱ��report recommends that species are only relocated when absolutely necessary and quarantine periods, tailored to stop transmission of the most likely pathogens being carried, are used.

It identifies four key factors that determine the risk of spreading pathogens when relocating animals: proportion of infected animals in both source and recipient populations; density of the resulting population; host immunity; and the life-cycle of the pathogen. Pathogens that must infect multiple species to complete their life-cycle, like parasitic mites, will only persist if all of the species are present in a given location.

“Moving animals to a new location is often used to protect or supplement endangered populations. But we must consider the risk this will spread pathogens that we don’t understand very well at all, which could put these populations in even greater danger,” said Josh Brian, a PhD student in the Department of Zoology at the ̽��ֱ�� of Cambridge and first author of the report.

Different populations of the same species may respond differently to infection with the same pathogen because of adaptations in their immune system. For example, a pack of endangered wolves moved to Yellowstone National Park died because the wolves had no immunity to parasites carried by the local canines.

̽��ֱ��researchers say that stocking rivers with fish for anglers, and sourcing exotic plants for home gardens could also move around parasites or diseases.

“Being aware of the risks of spreading diseases between populations is a vital first step towards making sure we avoid unintentional harm in future conservation work,” said Isobel Ollard, a PhD student in the Department of Zoology at the ̽��ֱ�� of Cambridge, who was also involved in the study.

This research was funded by the Woolf Fisher Trust.

Reference
Brian, J.I., Ollard, I.S., & Aldridge, D.C. ‘Don’t move a mussel? Parasite and disease risk in conservation action.’ Conservation Letters, April 2021. DOI: 10.1111/conl.12799

Moving endangered species to new locations is often used as part of species conservation strategies, and can help to restore degraded ecosystems. But scientists say there is a high risk that these relocations are accidentally spreading diseases and parasites.

We’ve seen that mixing different populations of mussels can allow widespread transmission of gonad-eating worms.

David Aldridge

At-risk species of river mussel

Yes

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