̽��ֱ�� of Cambridge - James Herbert-Read

Stealth swimmers: fish hide behind others to hunt

jg533 — Mon, 07 Aug 2023 15:02:33 +0000

A new study provides the first experimental evidence that the trumpetfish, Aulostomus maculatus, can conceal itself by swimming closely behind another fish while hunting – and reduce the likelihood of being detected by its prey.

In this ‘shadowing’ behaviour, the long, thin trumpetfish uses a non-threatening species of fish, such as parrotfish, as camouflage to get closer to its dinner.

This is the only known example of one non-human animal using another as a form of concealment.

̽��ֱ��research involved hours of diving in the Caribbean Sea, pulling hand-painted model fish along a wire.

“When a trumpetfish swims closely alongside another species of fish, it’s either hidden from its prey entirely, or seen but not recognised as a predator because the shape is different,” said Dr Sam Matchette, a researcher in the ̽��ֱ�� of Cambridge’s Department of Zoology and first author of the study.

Damselfish, Stegastes partitus, form colonies on the seafloor and are a common meal for trumpetfish. Working amongst the coral reefs off the Dutch Caribbean island of Curaçao, researchers set up an underwater system to pull 3D-printed models of trumpetfish on nylon lines past colonies of damselfish, and filmed their responses.

When the trumpetfish model moved past alone, damselfish swam up to inspect - and rapidly fled back to shelter in response to the predatory threat.

When a model of a herbivorous parrotfish, Sparisoma viride, moved past alone, the damselfish inspected and responded far less.

When a trumpetfish model was attached to the side of a parrotfish model – to replicate the shadowing behaviour of the real trumpetfish – the damselfish responded just as they had to the parrotfish model alone: they had not detected the threat.

Matchette said: “I was surprised that the damselfish had such a profoundly different response to the different fish; it was great to watch this happening in real time.”

̽��ֱ��study, involving collaborators at the ̽��ֱ�� of Bristol, is published in the journal Current Biology.

“Doing manipulative experiments in the wild like this allows us to test the ecological relevance of these behaviours,” said Professor Andy Radford in the ̽��ֱ�� of Bristol’s School of Biological Sciences, and coauthor of the study.

Matchette, along with his co-author and dive buddy Christian Drerup, spent hours underwater, barely moving, to conduct their experiment.

Their earlier questioning of divers working at dive shops in the Caribbean revealed that trumpetfish are commonly seen swimming alongside parrotfish and other reef fish – but the reason for this remarkable behaviour had not been tested.

In addition, divers were much more likely to have seen the shadowing behaviour on degraded, less structurally complex reefs.

Coral reefs around the world are being degraded due to the warming climate, pollution and overfishing. ̽��ֱ��researchers say the strategy of hiding behind other moving fish may help animals adapt to the impacts of environmental change.

“ ̽��ֱ��shadowing behaviour of the trumpetfish appears a useful strategy to improve its hunting success. We might see this behaviour becoming more common in the future as fewer structures on the reef are available for them to hide behind,” said Dr James Herbert-Read in the ̽��ֱ�� of Cambridge’s Department of Zoology, senior author of the study.

Human duck hunters historically hid behind cardboard cut-outs of domestic animals - called ‘stalking horses’ - to approach ducks without being detected. But this strategy has received little attention in non-human animals and has never been experimentally tested before.

̽��ֱ��research was funded by ̽��ֱ��Whitten Programme in Tropical and Aquatic Biology, ̽��ֱ��Association for the Study of Animal Behaviour, and ̽��ֱ��Fisheries Society of the British Isles.

Reference

Matchette, S R et al.: ‘Predatory trumpetfish conceal themselves from their prey by swimming alongside other fish.’ Current Biology, August 2023. DOI: 10.1016/j.cub.2023.05.075

An experiment on coral reefs provides the first evidence that predators use other animals for motion camouflage to approach their prey without detection.

̽��ֱ��shadowing behaviour of the trumpetfish appears a useful strategy to improve its hunting success.

James Herbert-Read

Stealth swimmers: the fish that hide behind others to hunt

Sam Matchette

Parrotfish model pulled across reef on a wire.

̽��ֱ��text in this work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 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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Experts predict top emerging impacts on ocean biodiversity over next decade

jg533 — Thu, 07 Jul 2022 15:08:56 +0000

An international team of experts has produced a list of 15 issues they believe are likely to have a significant impact on marine and coastal biodiversity over the next five to ten years.

Their ‘horizon scanning’ technique focuses on identifying issues that are not currently receiving widespread attention, but are likely to become important over the next decade. ̽��ֱ��aim is to raise awareness and encourage investment into full assessment of these issues now, and potentially drive policy change, before the issues have a major impact on biodiversity.

̽��ֱ��issues include the impacts of wildfires on coastal ecosystems, the effects of new biodegradable materials on the marine environment, and an ‘empty’ zone at the equator as species move away from this warming region of the ocean.

“Marine and coastal ecosystems face a wide range of emerging issues that are poorly recognised or understood, each having the potential to impact biodiversity,” said Dr James Herbert-Read in the ̽��ֱ�� of Cambridge’s Department of Zoology, joint first author of the paper.

He added: “By highlighting future issues, we’re pointing to where changes must be made today - both in monitoring and policy – to protect our marine and coastal environments.”

̽��ֱ��horizon scan involved 30 experts in marine and coastal systems from 11 countries in the global north and south, from a variety of backgrounds including scientists and policy-makers. ̽��ֱ��results are published today in the journal Nature Ecology and Evolution.

Several of the issues identified are linked to exploitation of ocean resources. For example, deep sea ‘brine pools’ are unique marine environments home to a diversity of life - and have high concentrations of salts containing lithium. ̽��ֱ��authors warn that rising demand for lithium for electric vehicle batteries may put these environments at risk. They call for rules to ensure biodiversity is assessed before deep sea brine pools are exploited.

While overfishing is an immediate problem, the horizon scan looked beyond this to what might happen next. ̽��ֱ��authors think there may soon be a move to fishing in the deeper waters of the mesopelagic zone (a depth of 200m – 1,000m), where fish are not fit for human consumption but can be sold as food to fish farms.

“There are areas where we believe immediate changes could prevent huge problems arising over the next decade, such as overfishing in the ocean’s mesopelagic zone,” said Dr Ann Thornton in the ̽��ֱ�� of Cambridge’s Department of Zoology, joint first author on the paper.

She added: “Curbing this would not only stop overexploitation of these fish stocks, but reduce the disruption of carbon cycling in the ocean - because these species are an ocean pump that removes carbon from our atmosphere.”

̽��ֱ��report also highlights the potential impact of new biodegradable materials on the ocean. Some of these materials are more toxic to marine species than traditional plastics.

Herbert-Read said: “Governments are making a push for the use of biodegradable materials - but we don’t know what impacts these materials may have on ocean life.”

̽��ֱ��authors also warn that the nutritional content of fish is declining as a consequence of climate change. Essential fatty acids tend to be produced by cold-water fish species, so as climate change raises ocean temperatures, the production of these nutritious molecules is reduced. Such changes may have impacts on both marine life and human health.

Not all of the predicted impacts are negative. ̽��ֱ��authors think the development of new technologies, such as soft robotics and better underwater tracking systems, will enable scientists to learn more about marine species and their distribution. This, in turn, will guide the development of more effective marine protected areas. But they also warn that the impacts of these technologies on biodiversity must be assessed before they are deployed at scale.

“Our early identification of these issues, and their potential impacts on marine and coastal biodiversity, will support scientists, conservationists, resource managers, policy-makers and the wider community in addressing the challenges facing marine ecosystems,” said Herbert-Read.

While there are many well-known issues facing ocean biodiversity including climate change, ocean acidification and pollution, this study focused on lesser-known emerging issues that could soon have significant impacts on marine and coastal ecosystems.

This horizon scanning process has previously been used by researchers from the Department of Zoology to identify issues that have later come to prominence, for example, a scan in 2009 gave an early warning that microplastics could become a major problem in marine environments.

̽��ֱ��United Nations has designated 2021-2030 as the ‘UN Decade of Ocean Science for Sustainable Development.’ In addition, the fifteenth Conference of the Parties (COP) to the United Nations Convention on Biological Diversity will conclude negotiations on a global biodiversity framework in late 2022. ̽��ֱ��aim is to slow and reverse the loss of biodiversity, and establish goals for positive outcomes by 2050.

This research was funded by Oceankind.

Reference

Herbert-Read, JE et al. ‘A global horizon scan of issues impacting marine and coastal biodiversity conservation.’ Nature Ecology and Evolution, July 2022. DOI: 10.1038/s41559-022-01812-0

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̽��ֱ��full list of issues identified by the report includes:

Ecosystem impacts

Wildfire impacts on coastal and marine ecosystems
Coastal darkening
Increased toxicity of metal pollution due to ocean acidification
Equatorial marine communities becoming depauperate (lacking variety) due to climate migration
Altered nutritional content of fish due to climate change

Resource exploitation

Untapped potential of marine collagens and their impacts on marine ecosystems
Impacts of expanding trade for fish swim bladders on target and non-target species
Impacts of fishing for mesopelagic (middle-depth) species on the biological ocean pump
Extraction of lithium from deep-sea brine pools

Novel technologies

Co-location of marine activities
Floating marine cities
Trace element contamination compounded by the global transition to green technologies
New underwater tracking systems to study non-surfacing marine animals
Soft robotics for marine research
Effects of new biodegradable materials in the marine environment

Lithium extraction from the deep sea, overfishing of deeper-water species, and the unexpected ocean impacts of wildfires on land are among 15 issues experts warn we ought to be addressing now.

By highlighting future issues, we’re pointing to where changes must be made today - both in monitoring and policy – to protect our marine and coastal environments

James Herbert-Read

Emma Johnston

Marine ecosystem

̽��ֱ��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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