̽��ֱ�� of Cambridge - David Aldridge

Remarkable squirting mussels captured on film

jg533 — Sat, 11 Mar 2023 09:00:43 +0000

In spring, female mussels were seen moving to the water’s edge and anchoring into the riverbed, with their back ends raised above the waterline.

Then they squirted out regular water jets, which landed in the water up to a metre away. Squirting cycles lasted 3-6 hours.

This behaviour has never been seen in any other mussel species.

̽��ֱ��jets disturb the river surface and attract fish. Mussel larvae in the jets can then attach to the gills of the fish and complete their metamorphosis into adults.

“Who'd have thought that a mussel, that doesn't even have a head or a brain, knows to move to the river margin and squirt jets of water back into the river during springtime? It’s amazing!” said Professor David Aldridge in the ̽��ֱ�� of Cambridge’s Department of Zoology, lead author of the report published today in the journal Ecology.

Unlike other mussel species, Unio crassus has a limited range of suitable host fishes – including minnows and chub. These species were attracted to the falling water jets.

̽��ֱ��researchers think the mussels squirt water jets to increase the chances of their larvae attaching to the right host fishes. By being squirted into the air and not the water, the larvae are propelled greater distances from the parent mussel.

̽��ֱ��study was carried out during spring in the Biała Tarnowska River, Poland. Six squirts were collected from each mussel for analysis – which confirmed that they contained viable mussel larvae.

Before now, there was only anecdotal evidence of this behaviour. Some scientists thought the water jets might be a way for the mussels to expel faeces.

This behaviour could explain why Unio crassus is an endangered species. Climbing out of the water to squirt makes it vulnerable to floods, destruction of river margins, and predators like mink. And its need for specific host fishes links its survival to theirs.

Understanding how this species completes its life cycle is important for its conservation under changing environmental conditions.

Reference

Aldridge, D C et al: Fishing for hosts: larval spurting by the endangered thick-shelled river mussel, Unio crassus. Ecology, March 2023. DOI: 10.1002/ECY.4026

Cambridge researchers have observed a highly unusual behaviour in the endangered freshwater mussel, Unio crassus.

Who'd have thought that a mussel, that doesn't even have a head or a brain, knows to move to the river margin and squirt jets of water back into the river during springtime?

David Aldridge

Spurting Mussel Movie

Mussel squirting a water jet

̽��ֱ��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.

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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

Yes

Natural clean-up: bacteria can remove plastic pollution from lakes

jg533 — Tue, 26 Jul 2022 15:18:01 +0000

̽��ֱ��bacteria break down the carbon compounds in plastic to use as food for their growth.

̽��ֱ��scientists say that enriching waters with particular species of bacteria could be a natural way to remove plastic pollution from the environment.

̽��ֱ��effect is pronounced: the rate of bacterial growth more than doubled when plastic pollution raised the overall carbon level in lake water by just 4%.

̽��ֱ��results suggest that the plastic pollution in lakes is ‘priming’ the bacteria for rapid growth – the bacteria are not only breaking down the plastic but are then more able to break down other natural carbon compounds in the lake.

Lake bacteria were found to favour plastic-derived carbon compounds over natural ones. ̽��ֱ��researchers think this is because the carbon compounds from plastics are easier for the bacteria to break down and use as food.

̽��ֱ��scientists caution that this does not condone ongoing plastic pollution. Some of the compounds within plastics can have toxic effects on the environment, particularly at high concentrations.

̽��ֱ��findings are published today in the journal Nature Communications.

“It’s almost like the plastic pollution is getting the bacteria’s appetite going. ̽��ֱ��bacteria use the plastic as food first, because it’s easy to break down, and then they’re more able to break down some of the more difficult food – the natural organic matter in the lake,” said Dr Andrew Tanentzap in the ̽��ֱ�� of Cambridge’s Department of Plant Sciences, senior author of the paper.

He added: “This suggests that plastic pollution is stimulating the whole food web in lakes, because more bacteria means more food for the bigger organisms like ducks and fish.”

̽��ֱ��effect varied depending on the diversity of bacterial species present in the lake water – lakes with more different species were better at breaking down plastic pollution.

A study published by the authors last year found that European lakes are potential hotspots of microplastic pollution.

When plastics break down they release simple carbon compounds. ̽��ֱ��researchers found that these are chemically distinct to the carbon compounds released as organic matter like leaves and twigs break down.

̽��ֱ��carbon compounds from plastics were shown to be derived from additives unique to plastic products, including adhesives and softeners.

̽��ֱ��new study also found that bacteria removed more plastic pollution in lakes that had fewer unique natural carbon compounds. This is because the bacteria in the lake water had fewer other food sources.

̽��ֱ��results will help to prioritise lakes where pollution control is most urgent. If a lake has a lot of plastic pollution, but low bacterial diversity and a lot of different natural organic compounds, then its ecosystem will be more vulnerable to damage.

“Unfortunately, plastics will pollute our environment for decades. On the positive side, our study helps to identify microbes that could be harnessed to help break down plastic waste and better manage environmental pollution," said Professor David Aldridge in the ̽��ֱ�� of Cambridge’s Department of Zoology, who was involved in the study.

̽��ֱ��study involved sampling 29 lakes across Scandinavia between August and September 2019. To assess a range of conditions, these lakes differed in latitude, depth, area, average surface temperature and diversity of dissolved carbon-based molecules.

̽��ֱ��scientists cut up plastic bags from four major UK shopping chains, and shook these in water until their carbon compounds were released.

At each lake, glass bottles were filled with lake water. A small amount of the ‘plastic water’ was added to half of these, to represent the amount of carbon leached from plastics into the environment, and the same amount of distilled water was added to the others. After 72 hours in the dark, bacterial activity was measured in each of the bottles.

̽��ֱ��study measured bacterial growth - by increase in mass, and the efficiency of bacterial growth - by the amount of carbon-dioxide released in the process of growing.

In the water with plastic-derived carbon compounds, the bacteria had doubled in mass very efficiently. Around 50% of this carbon was incorporated into the bacteria in 72 hours.

"Our study shows that when carrier bags enter lakes and rivers they can have dramatic and unexpected impacts on the entire ecosystem. Hopefully our results will encourage people to be even more careful about how they dispose of plastic waste," said Eleanor Sheridan in the ̽��ֱ�� of Cambridge’s Department of Plant Sciences, first author of the study who undertook the work as part of a final-year undergraduate project.

̽��ֱ��research was funded by the European Research Council.

Reference

Sheridan, EA et al: ‘Plastic pollution fosters more microbial growth in lakes than natural organic matter.’ Nature Communications, 2022. DOI: 10.1038/s41467-022-31691-9

A study of 29 European lakes has found that some naturally-occurring lake bacteria grow faster and more efficiently on the remains of plastic bags than on natural matter like leaves and twigs.

It’s almost like the plastic pollution is getting the bacteria’s appetite going. ̽��ֱ��bacteria use the plastic as food first, because it’s easy to break down.

Andrew Tanentzap

SG Woodman

Study lake in Norway

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BioBullets protect UK water industry

lw355 — Thu, 05 May 2022 07:00:31 +0000

How do you deal with a harmful invasive species wreaking havoc on the UK’s water pipes? You take advantage of them being fussy eaters and send them a Trojan Horse.

Invasive species ‘hitchhiking’ on ships threaten Antarctica’s ecosystems

jg533 — Mon, 10 Jan 2022 20:33:31 +0000

Marine life hitching a ride on ocean-crossing ships poses a threat to Antarctica’s pristine ecosystems, with the potential for invasive species to arrive from almost anywhere across the globe.

Crayfish and carp among invasive species pushing lakes towards ecosystem collapse

jg533 — Wed, 06 Oct 2021 23:01:00 +0000

Human activity and climate change are causing invasive non-native species to spread rapidly across the globe. Researchers have found that certain invasive species can push lake ecosystems beyond a critical ‘tipping point’, causing a sudden shift from healthy to degraded conditions that is difficult to reverse.

Invasive fish such as Asian silver carp Hypophthalmichthys molitrix, and crustaceans such as American signal crayfish Pacifastacus leniusculus, were found to significantly reduce the abundance of other important organisms in lakes and degrade water quality. ̽��ֱ��findings, published today in the journal Global Change Biology, also provide guidance on the best ways to manage waterbodies.

Shallow lakes naturally exist in one of two alternative stable states: either healthy - with clear water with an abundance of vegetation, or degraded - with cloudy water dominated by algae. When a lake is in the latter state, algae use up all the nutrients in the water and block sunlight, preventing the growth of aquatic vegetation that would aid ecosystem recovery.

Deteriorated, algae-dominated freshwater ecosystems also threaten the health and water security of human populations. Blooms of cyanobacteria, known as ‘blue-green algae’ can produce toxins that contaminate food webs and poison water supplies.

“Algal blooms represent one of the most significant threats to the security of the Earth’s surface freshwaters. Simply undoing the circumstances that triggered a tipping point will not restore the ecosystem - the road to recovery is slow and steep,” said Dr Sam Reynolds in the ̽��ֱ�� of Cambridge’s Department of Zoology, first author of the report.

However, although invasive species are recognised as a significant threat to global biodiversity, their impacts on ecosystem services may not be uniformly negative. Invasive molluscs, including the zebra mussel Dreissena polymorpha, were found to engineer the opposite biological and environmental response: they delay ecosystem collapse and potentially aid the recovery of degraded lake ecosystems.

“Managers of drinking water reservoirs, for example, may be able to avoid the cost of dealing with blooms of harmful algae, by removing invasive crayfish but allowing established non-native zebra mussels to remain and act as biological filters,” said Professor David Aldridge, senior author of the report.

He added: “Early detection and rapid response plans should always be our first line of attack. But in situations where invaders have already established and can no longer be eradicated, it may be appropriate to embrace their positive effects.”

̽��ֱ��researchers focused on shallow lake ecosystems, but say that their framework could be applied to other critical ecosystems that experience catastrophic tipping points - such as coral reefs, kelp forests and desert shrublands.

This research was funded by the Biotechnology and Biological Sciences Research Council (BBSRC).

Reference
Reynolds, SA & Aldridge, DC: 'Global impacts of invasive species on the tipping points of shallow lakes'. Global Change Biology, October 2021. DOI 10.1111/gcb.15893

Certain invasive, non-native species can disrupt lakes to the point of rapid ecosystem collapse, contaminating water for drinking, aquaculture and recreation, a new study has found.

Simply undoing the circumstances that triggered a tipping point will not restore the ecosystem - the road to recovery is slow and steep.

Sam Reynolds

Mark Philpott on Flickr

American signal crayfish

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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

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