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Degraded coral reefs are far quieter than five years ago, and no longer sound like suitable habitat to young fish searching for a place to live and breed, according to research published today in Proceedings of the National Academy of Sciences USA.
Baby fish looking for a home can use noisy coral reef sounds including snapping shrimp clicks, damselfish chirps, and clownfish chattering to locate and select suitable habitat. But that ?coral reef orchestra? has been quietened following recent cyclone and coral bleaching damage on the Great Barrier Reef, raising fears that young fish may no longer hear their way home.
An international team of scientists led by the University of Exeter carried out field experiments on the Northern Great Barrier Reef, and found that reefs sound much quieter and less acoustically diverse than they did before three years of cyclones and coral bleaching. The soundscapes of these recently degraded reefs are less attractive to juvenile fishes, attracting 40% fewer fish compared to the sound of previous healthy reefs.
Lead author Tim Gordon, a marine biologist at the University of Exeter, said: ?It?s heart-breaking to hear. The usual pops, chirps, snaps and chatters of countless fish and invertebrates have disappeared. The symphony of the sea is being silenced.?
This loss of attractiveness of reef sounds to fish in the sea could have devastating consequences for reefs. Fish communities are instrumental in maintaining healthy reefs, by removing algae, facilitating coral growth, contributing to nutrient cycles and keeping food webs in balance. Damaged reefs with healthy fish populations recover faster than reefs that have lost their fish.
Harry Harding, co-author from the University of Bristol, explains: ?If fish aren?t hearing their way home anymore, that could be bad news for the recovery prospects of reefs. Fish play critical roles on coral reefs, grazing away harmful algae and allowing coral to grow. A reef without fish is a reef that?s in trouble.?
Coral reef animals produce a dazzling array of sounds to communicate with each other while hunting, to warn each other about the approach of predators and to impress each other during courtship. Together, these sounds combine to form a ?soundscape? that can be heard for miles around. This soundscape provides a valuable cue for young fish to locate and select habitat after a period of early development in the open ocean.
Gordon said: ?Being able to hear the difference really drives home the fact that our coral reefs are being decimated. Some of the most beautiful places on Earth are dying due to human activity, and it is up to us to fix it.?
The scientists from the University of Exeter, University of Bristol, Cefas (Centre for Environment, Fisheries and Aquaculture Science), Duke University (USA), the Australian Institute of Marine Science and James Cook University (Australia) built experimental reefs from coral rubble on sand flats, then used underwater loudspeakers to broadcast healthy coral reef sounds or degraded coral reef sounds, to see which sounds attracted more young fish.
Senior author Steve Simpson, Associate Professor in Marine Biology & Global Change at the University of Exeter, said: ?Over the last 15 years my research group have discovered how important sound can be for fish to locate and select specific reefs. We have marvelled at the remarkable diversity and complexity of coral reef soundscapes. But in the last few years the reefs we know and love have died before our eyes. And the deserted and crumbling rubble fields have turned eerily quiet.?
Professor Simpson added: ?If the reefs have gone quiet, then the chances of the next generation of fish recolonising the reefs are much reduced. Without fish, the reefs can?t recover.?
Warming seas increase the frequency and severity of coral bleaching events worldwide, as higher temperatures cause a breakdown in the relationship between corals and the zooxanthellae that they host in their tissue, providing their energy through photosynthesis. This bleaching recently killed up to 80% of corals in some areas of the Great Barrier Reef, and bleaching events of this nature are happening worldwide four times more frequently than they used to.
Reductions in carbon emissions are needed to reduce this damage, as Gordon explains: ?The damage we?ve done to reefs worldwide is horrific, but the fight isn?t over yet. If we can fulfil our international commitments to dramatically reduce carbon emissions, it?s still possible to protect some of the reefs that are left. The time for action is now.?
The research came out in the Proceedings of the National Academy of Science USA click here for a pdf of the paper
Tim Gordon, Professor Steve Simpson and Professor Mark McCormick are available for interview.
Contact Tim Gordon on or ; contact Professor Steve Simpson on or .
High-quality pictures, audio recordings and videos of coral reefs, including both usual and ?degraded? sounds, are available at this link. A 1-minute long summary video of the findings, featuring footage and recorded sounds of healthy and degraded reefs, is also available here. https://www.dropbox.com/sh/s146nqpsf0yh8m8/AACKSgjgCnoCJS0u2O5z3ttPa?dl=0
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Embargoed to Sunday 30 July 2017
Dr. Jen Atherton and Prof. Mark McCormick, both at the ARC Centre of Excellence for Coral Reef Studies (Coral CoE) at James Cook University, found that young damselfish imprint on the odours of their closely related kin whilst they are still only embryos.
?These fish can detect and recognise cues from their siblings quite early on in their development,? says Dr. Atherton, ?They start to panic when they pick up the scent of an injured relative.?
Dr. Atherton adds that she discovered a highly sophisticated sense of smell: ?The most amazing thing is, not only can the baby damselfish identify cues from other sibling fish with the same parents - they can differentiate between the fish of different parents, and also different species altogether,? she explains. ?These fish are only about eight days old and haven?t even hatched yet!?
This capability may be an important tool for the fish to help them avoid predators, with the early recognition of odours helping to reduce their chances of being eaten.
?These fish can increase their chance of survival not only through cooperating with their kin, who will help alert them to danger, but they may also use these scents to select ?safe? habitats,? Dr. Atherton said.
The study involved the embryos of two species of common coral reef damselfish ? the cinnamon clownfish, and the spiny chromis. ?To our knowledge, this is the first study to demonstrate kin recognition in a coral reef fish species, and even more remarkably this recognition develops among newly hatched larvae.
The study was a lab-based experiment, measuring fish embryo heart rates under a microscope ? the embryos are transparent, so each individual heartbeat can be seen and counted.
?Looking at the change in heart rate from before and after the introduction of certain odours allowed us to quantify the fish embryo?s reaction to it,? says Dr. Atherton. She found different responses between kin, non-kin of the same species, and other species.
Damselfish are a diverse group of fish commonly found on coral reefs around the world. They perform many important functions that can promote the health of reef habitats.
The study ?Kin recognition in embryonic damselfishes? is published in the journal Oikos click here
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Prof Mark McCormick
Chief Investigator, ARC Centre of Excellence for Coral Reef Studies
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Dr Jennifer Atherton
ARC Centre of Excellence for Coral Reef Studies & James Cook University
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Catherine Naum
Communications Manager
ARC Centre of Excellence for Coral Reef Studies
James Cook University
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Coral reef fish get stressed and lose weight if they are separated from each other, according to new research on the Great Barrier Reef.
For the first time, researchers from the ARC Centre of Excellence for Coral Reef Studies at James Cook University have succeeded in measuring the metabolic rates of individual fish in shoals to better understand why they prefer to socialise.
?We have suspected that shoaling fish gain a ?calming effect? from living in a group. But up until now we have been unable to measure how widely spread this effect is in individual fish,? says lead author Lauren Nadler.
Her team captured shoals of the blue-green damselfish, Chromis viridis, near Lizard Island on the Great Barrier Reef. The fish were then either isolated or kept together in shoals.
?The fish that were isolated lost weight after the first week, which meant they were less healthy than those in groups,? Nadler says.
The metabolic rate (an indicator of stress) of all fish was then measured both in a shoal and alone.
?Fish were calmer and less stressed when they had their shoal-mates around, with a 26% decrease in metabolic rate compared to individuals tested alone.?
?If these fish were out in the ocean by themselves, in order to stay alive, they would need more food to keep up their energy. Since they don?t have their buddies around to help look out for looming predators, foraging for food would be riskier,? says Professor Mark McCormick.
?The extra energy fish gain from shoaling is so important because it allows them to survive and reproduce and to pass on their genes to the next generation of fish,? he says.
One way fish can become separated from each other is through natural disturbances like tropical cyclones.
?When category 4 Cyclone Nathan passed over Lizard Island last year, we saw a number of blue-green damselfish living by themselves on small coral colonies. They were apparently separated from their group by the sheer force of the storm and currents.
The paper Shoaling reduces metabolic rate in gregarious coral reef fish species has been published in the Journal of Experimental Biology
Paper
Lauren Nadler, Shaun Killen, Eva McClure, Philip Munday, Mark McCormick. Shoaling reduces metabolic rate in gregarious coral reef fish speciesJournal of Experimental Biology 2016: doi:10.1242/jeb.139493 click here for pdf
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Australia?s worst-ever coral bleaching event is endangering the lives of reef fish who are unable to identify new predators.
Researchers from Australia and Sweden found that the damage to corals from bleaching prevents the common damselfish from responding to the tell-tale chemicals that indicate hungry predators are approaching.
?Baby fish use chemical alarm signals released from the skin of attacked individuals to learn the identity of new predators,? says Professor Mark McCormick from the ARC Centre of Excellence for Coral Reef Studies at James Cook University.
?They mix the alarm cue from their wounded buddy with the smell or sight of the responsible predator, allowing them to learn which individuals are dangerous and should be avoided in the future.
?We found that the chemical alarm only worked on damselfish on live coral. Their counterparts on dead coral failed to pick up the scent.? Dr. Oona Lönnstedt from Uppsala University in Sweden explains, ?We found that when corals die and become covered in algae the olfactory landscape of the reef seems to change, which affects this crucial learning mechanism used by fish.?
?If the process of cataloguing and avoiding predators is hindered in some species by coral degradation and loss, then much of the diversity of reef fish could be lost too,? she says.
?Many reef fish need specific habitats that only healthy coral reefs can provide.?
?The Great Barrier Reef is currently experiencing the worst mass coral bleaching event in its history and coral cover on the majority of reefs is declining sharply,? says Prof. McCormick.
?If dead coral masks key chemical signals used to learn new predators, the replenishment of reefs could be seriously threatened.?
The study by Professor McCormick and Dr. Oona Lönnstedt has been published today in the journal Proceedings of the Royal Society B.
Paper
McCormick M.I., Lönnstedt O.M. 2016 Disrupted learning: habitat degradation impairs crucial antipredator responses in naďve prey. Proceedings of the Royal Society B 20160441. (doi:10.1098/rspb.2016.0441). click here for paper
Contacts:
Professor Mark McCormick, ARC Centre of Excellence for Coral Reef Studies, James Cook University
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Scientists have discovered that the presence of large fish predators can reduce stress on baby fish.
The researchers - from the ARC Centre of Excellence for Coral Reef Studies, James Cook University and the University of Glasgow- have found that physiological stress on baby fish can be reduced by more than a third if large predatory fish are around to scare off smaller, hungry predators, known as mesopredators.
?Previous studies have proven that the sight of large predators can reduce the activity of mesopredators,? explains Maria del Mar Palacios, leading author of the research. ?But our study is the first to show that such behavioural control on mesopredators is strong enough to indirectly allow baby fish to reduce stress levels by more than 35 %.?
To obtain these results, scientists exposed baby damselfish to combinations of sensory cues (including visual and scent cues) from small and large predators. Detailed measures of the behaviour and oxygen uptake (as proxy for ?stress?) of the baby fish enabled researchers to understand the cascading effects that predators throughout the food chain can have on newly settled baby fish on the Great Barrier Reef.
JCU collaborator Lauren Nadler said the baby fish got very scared in the presence of mesopredators alone. However, all the physiological stress disappeared if they added a large predator, which effectively suppressed all mesopredator activity. ?By scaring the mesopredator, it seems as if the large predators are helping the baby fish keep calm and relaxed. They don?t need to worry anymore about the constant chases and threats from mesopredators?.
As with humans, it?s expected that a reduction in physiological stress should benefit their fitness and well-being.
?Animals have finite energy budgets, so by reducing the energy invested in antipredator responses, baby fish should be able to invest more energy in growth and storage,? said Dr. Shaun Killlen, a fish physiologist from the University of Glasgow who also collaborated on the study.
Professor Mark McCormick, who supervised the research, warned that although these findings are exciting from an ecological point of view, they could carry grave consequences for the balance of marine ecosystems.
?The ongoing overexploitation of large marine carnivores might allow an explosion of smaller, active predators that could not only kill, but also stress the population of baby fish that remain? he said.
Paper:
M.M. Palacios, S.S. Killen, L.E. Nadler, J.R. White &, M.I. McCormick. 2016. Top-predators negate the effect of mesopredators on prey physiology. Journal of Animal Ecology. click here
Contacts:
Funding Bodies:
ARC Centre of Excellence for Coral Reef Studies
College of Marine & Environmental Sciences at James Cook University
Australian Coral Reef Society
Ian Potter Doctoral Fellowship at Lizard Island
Lizard Island Reef Research Foundation Doctoral Fellowship
Natural Environment Research Council, UK
A coral trout (large predator) protecting a baby damselfish from small-hungry mesopredators at Lizard Island, Great Barrier Reef. Photo: MM. Palacios
Baby damselfish hiding among coral branches. Photo: MM. Palacios
A James Cook University scientist says a pioneering new study shows the rate fish are captured by predators can double when boats are motoring nearby.
Professor Mark McCormick was part of an international research team that found noise from passing motorboats increases stress levels in young coral reef fish and reduces their ability to flee from predators. As a consequence they are captured more easily and their survival chances are halved.
It?s the first study to show that real-world noise can have a direct consequence on fish survival. ?It shows that juvenile fish become distracted and stressed when exposed to motorboat noise and predators capitalise on their indecision?, said Professor McCormick.
The study was led by Dr Stephen Simpson from the University of Exeter and funded by the UK?s Natural Environment Research Council (NERC).
The team of scientists included Australian and Canadian researchers specialising in predator¬?prey interactions and bioacousticians from the University of Bristol.
They combined laboratory and field experiments, using playbacks and real boat noise, to test the impact of motorboat noise on survival of young Ambon damselfish during encounters with their natural predator the dusky dottyback.
?We found that when real boats were motoring near to young damselfish in open water, they became stressed and were six times less likely to startle to simulated predator attacks compared to fish tested without boats nearby,? said Dr Simpson
The team is optimistic about the possibilities for management of noise and its potential impact. ?If boat noise turns out to be a general problem then this suggests fish at young stages can be quite vulnerable,? said Professor McCormick. ?But young fish are mostly around in summer and during the new moon, so we may only need some regulations at key points to reduce the impact of noise.?
Managing local environmental stressors such as noise is an essential first step in protecting the marine environment. ?You might argue that climate change is a bigger threat to reef life, but if we can reduce the effect of local noise pollution we build greater resilience in reef communities to looming threats such as global warming and ocean acidification,? said collaborator Dr Mark Meekan, Australian Institute of Marine Science.
25 January, 2016
Researchers at the ARC Centre of Excellence for Coral Reef Studies at James Cook University have found that long hot summers can wreak havoc on the development of coral reef fish.
In one of the longest studies of its kind, the researchers examined the impacts of water temperature, wind, rainfall and solar radiation on damselfish larvae around Lizard Island at the northern end of the Great Barrier Reef.
?We found that when ocean temperatures warmed beyond about 28°C, the pace of larval development slowed,? said study lead author, Dr Ian McLeod.
?The findings are a concern,? said study co-author, Professor Mark McCormick.
?To see adverse effects over the current-day temperature range raises concerns about the serious negative effects we may see when the ocean temperature warms with climate change.?
Most marine fishes go through a larval development stage in the open ocean when they are more vulnerable to predators.
Dr McLeod said the longer larvae remain in this stage the less likely they are to survive.
?Faster growth during the larval stage should lead to a survival advantage because they can develop sooner and get out of the dangerous pelagic environment faster,? he says.
However there is a ray of hope. The researchers also found a high level of variability in larval development in relation to temperature and other weather conditions.
?This high level of variability likely means that some fish will thrive in the changing conditions and pass on their genes to future generations? said Dr McLeod.
The authors hope that the results for this study will be used to help predict the effects of climate change on larval development of fishes.
Dr Ian McLeod is a former PhD Candidate at ARC Coe and is now a Senior Research Scientist at TropWATER, James Cook University.
Contacts:
Dr Ian McLeod
Paper:
Interannual variation in the larval development of a coral reef fish in response to temperature and associated environmental factors, by Ian M. McLeod, Rhondda E. Jones, Geoffrey P. Jones, Miwa Takahashi and Mark I. McCormick is published in the journal, Marine Biology. DOI 10.1007/s00227-015-2765-y
http://goo.gl/tZgkRG
28th October 2015
Distressed damsels cry for help
Researchers at the ARC Centre of Excellence for Coral Reef Studies at James Cook University have found that fish release a chemical ?distress call? when caught by predators, dramatically boosting their chances of survival.
Fish harbour a chemical substance in their skin that?s released upon injury. It triggers fearful and escape behaviour in nearby fish, but until now scientists hadn?t identified the benefits to the sender.
?For decades scientists have debated the evolutionary origin of chemical alarm cues in fish,? says study lead author, Dr. Oona Lönnstedt, currently a post-doctoral fellow at the University of Uppsala, Sweden.
The researchers have now found the answer, discovering that the chemical cue attracts additional predators to the capture site.
?Chemical alarm cues in fish seem to function in a similar way to the distress calls emitted by many birds and mammals following capture,? says study co-author Professor Mark McCormick.
?When damselfish release their chemical alarm on a coral reef, lots of additional predators are attracted to the cue release area,? says Professor McCormick.
?More predators would seem to mean more trouble, but we discovered that additional predators interfere with the initial predation event, allowing the prey a greater chance to escape.?
The research team found the new predators would attempt to steal the prey, and in the ensuing commotion the captured damselfish had a greater chance to break free and hide.
?When caught by a predator, small damselfish have almost no chance of escaping their fate as the predator?s next meal. However, when another fish predator is attracted to the capture site, prey will escape about 40 percent of the time,? says Professor McCormick.
Dr Lönnstedt says this proves that chemical alarm cues benefit the sender by giving it a much greater chance of not ending up as dinner.
?These findings are the first to demonstrate an evolutionary mechanism by which fish may benefit from the production and release of chemical alarm cues, and highlight the complex and important role chemical cues play in predator-prey interactions on coral reefs.? Dr. Lönnstedt says.
?It all goes to show that coral reef fish have evolved quite a range of clever strategies for survival which are deployed when a threatening situation demands.?
Paper: Damsel in distress: captured damselfish prey emit chemical cues that attract secondary predators and improve escape chances by Oona Lönnstedt and Mark McCormick is published in the journal Proceedings of the Royal Society B.
Images: please credit all images - Oona Lönnstedt
Contacts:
Eleanor Gregory, Communications Manager
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17th October 2013
?Ghost? fish are taking over the Caribbean
A spiny, toxic and beautiful member of the world?s coral reef communities, the Red Lionfish is invisible to the small fish it likes to eat. A new study by James Cook University scientists Oona Lönnstedt and Professor Mark McCormick suggests this is one reason for the lionfishes? incredible success in the Caribbean, where it is eating its way through the reef ecosystem.
?Lionfish are native to the Pacific, but have been taking over the Caribbean Basin ever since they were accidentally introduced almost 30 years ago. Their extreme success as an invasive predator has long been a mystery to ecologists worldwide,? Professor McCormick explains.
The new research, published in the latest issue of PLoS ONE suggests that the solution in part lies in the power of camouflage, as these voracious carnivores are virtually undetectable by small prey fish.
Red lionfish (Pterois volitans) are a rare and beautiful sighting for divers in their native waters around the Great Barrier Reef. However, in the reefs around the Florida coast and Caribbean they are viewed as a huge nuisance. For over a decade, scientists have tried their best to understand how these gorgeous but deadly predators can wreak such havoc on their invaded ecosystem. Almost all of the work to date has focussed on the consequences of the interaction between these predators and their prey in areas where lionfish are invasive species.
Now, as a world first, graduate student Ms Lönnstedt and Professor McCormick have found that lionfish in their native system are undetectable by prey, acting as ghosts able to feed on anything and everything without being discovered until it?s too late. ?We tested the response of small prey fish to three different predators, one of them the lionfish,? Ms Lönnstedt says. ?Surprisingly, the common prey fish were unable to learn that the lionfish represented a threat, which was very different to their response to two other fish predators. Lionfish were able to sneak up on their prey and capture every single one, while the other predators had much lower feeding success.?
This ability to bypass a very well-studied learning mechanism commonly used by prey to learn new risks is a world first, and has in part lead to the astounding success of lionfish in the Caribbean.
With release from any natural enemies in their new system and no problem catching food, the lionfish are practically unstoppable. The paper ?Ultimate Predators: lionfish have evolved to circumvent prey risk assessment abilities? is published in the latest issue of PLOS ONE.
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19th August 2013
FISH INTEGRATE VISUAL AND OFACTORY SENSORY CUES TO ASSESS PREDATION RISK
Anemonefish integrate information from visual and olfactory cues to modify their antipredator behaviours, with visual cues from neighbouring anemonefish being prioritised over olfactory cues. the study reported in the Animal Behaviour, suggests that by incorporating information from several sensory systems fish are able to get a better idea of the threats present in their environment.
In diverse and complex environments that support an abundance of predators, accurately assessing any potential danger in the local area is critically import if fish are to survive. Using olfactory and visual cues fishes can detect if there are any predators around and alter their behaviour, such as their proximity to shelter, in a way that increases survival. However, information from these senses is not always accurate. For example, visual cues can be obstructed by the complex environment and the information from olfactory cues is dependent on how water movement carries the odours.
In a new study, Rachael Manassa and colleagues investigated how fish incorporate information from different sensory systems to modify their antipredator responses and how they prioritise information from different sources. By exposing fish to chemical alarm cues (an odour that induces antipredator responses) in the presence or absence of a shoal of anemonefish, they demonstrated that fish significantly reduced their antipredator behaviours compared to when there was no shoal present. The results suggest that visual information available from the shoal modified the antipredator response to olfactor cues and allowed fish to optimise their antipredator response to increase their chances of survival.
The study, "Coral reef fish incorporate multiple sources of visual and chemical information to mediate predation risk", by Rachael Manassa, Danielle Dixson, Mark McCormick, Doug Chivers appears in Animal Behaviour (In Press). http://dx.doi.org/10.1016/j.anbehav.2013.07.003 Download PDF
30th July 2013
A HAPPY ENDING? INCREASING OCEANIC CO2 STIMULATES INCREASED REPRODUCTION IN CORAL REEF FISH
The world?s oceans are under threat from increased uptake carbon dioxide (CO2), leading to ocean acidification. Understanding the ability of marine organisms to not only survive, but also reproduce in these new conditions, is crucial for effective management of marine resources. We studied the reproduction of a coral reef fish under various CO2 conditions, projected to occur by years 2050 and 2100. Surprisingly we found an increase in reproduction with increasing CO2, with no apparent cost to adult condition. However, there may be longer-term impacts that we could not detect, such as reductions in subsequent breeding events.
The study "Increased CO2 stimulates reproduction in a coral reef fish" by GM Miller, S Watson, MI McCormick and PL Munday appears in Global Climate Change Biology (2013) doi: 10.1111/gcb.12259. Download PDF
30th July 2013
PREDATORS ALTER GROWTH PATTERNS IN AND EYESPOT DEVELOPMENT IN PREY
Young Ambon damselfish that are exposed to predators tend to develop larger false eyespots, as well as undergoing a corresponding reduction in the growth of their eyes. The research, published in Scientific Reports this week, suggests that size of eyespots may be plastic and can evolve to suit certain environmental conditions.
Many fishes and terrestrial insects sport false eyespots: large dark circles surrounded by a lightly coloured ring, mimicking the appearance of a vertebrate eye. Ambon damselfish (Pomancentrus amboinensis) make their home on the Great Barrier Reef, where they are highly vulnerable to predation. Juveniles have a lightly coloured body and a conspicuous eyespot on the upper rear fin, which fades away as the animal approaches maturation. Oona Lönnstedt and colleagues show that the size of these eyespots can increase upon exposure to predators, a change that is accompanied by reduced growth of the damselfish?s eyes. Damselfish that were exposed to predators seemed to experience higher survival rates compared to those exposed to herbivores or those isolated from other fish, the findings reveal.
The study suggests that false eyespots may represent a short-term adaptation to the presence of predators, potentially functioning to misdirect predator strikes and/or to protect the head region from fatal attacks. The results hint at the importance of experience with predators to prey survival early in life.
The study "Predator-induced changes in the growth of eyes and false eyespots" by Lonnstedt OM, McCormick MI and Chivers DP appears in Scientific Reports (2013) 3:2259 Download PDF
24th July 2013
A Comparison of Measures of Boldness and Their Relationships to Survival in Young Fish
Many different measures have been used to assess boldness, or risk-taking behavior, in animals. However, investigations of how these boldness measures compare to each other are rare. Also, it was unknown in how these variations of boldness measures relate to survivorship under natural conditions, an ecologically important tradeoff which is thought to be highly influenced by an individual?s unique behavior. In the present study we assessed boldness in juvenile damselfish using a variety of commonly used tests. This study found most measures had some overlap in the way they quantified boldness, yet were not necessarily interchangeable. Multiple measures of boldness are necessary to examine this behavior in a robust way and the appropriate tests are context dependent.
The paper ?A Comparison of Measures of Boldness and Their Relationships to Survival in Young Fish? by James R. White, Mark G. Meekan, Mark I. McCormick, and Maud C.O. Ferrari appears in PLoS ONE. Download PDF
12 July2013
FEAR OF THE DARK? FISH CAN LEARN ABOUT PREDATORS FROM OTHERS EVEN IN THE DARK
In complete darkness coral reef fish are capable of transmitting the recognition of a predator to individuals of the same species, through the process of social learning. The present study demonstrates for the first time that visual cues are not the only sensory stimuli relied upon for information transfer. Along with this, when threatened, individuals release chemical cues, known as disturbance cues, into the water. These cues induce a fear response; however they do not allow individuals to learn a predator. As such, it is likely that fish simultaneously use information from multiple cues to learn about predators.
The paper "Social learning of predators in the dark: understanding the role of visual, chemical and mechanical information" by Rachael Manassa, Mark McCormick, Doug Chivers and Maud Ferrari appears in Proceeding of the Royal Society B. Download PDF
20 June 2013
OXYGEN TRANSPORT KEY TO THE SUCCESS OF FISHES
Almost all vertebrates possess an oxygen-transporting protein within their blood called haemoglobin. In the lungs or gills of animals, haemoglobin rapidly absorbs oxygen from the environment they breathe (air or water), which greatly increases the amount of O2 that can be carried in the blood. When the blood arrives at the tissues (such as heart and muscle), the haemoglobin delivers oxygen for metabolism, which fuels life. The haemoglobin is found within red blood cells, and the environment within the cells determines how the haemoglobin holds onto or releases oxygen.
For over a century, scientists have studied how the end products of metabolism (CO2 and acid) stimulate haemoglobin to release oxygen to the tissues. In most vertebrates, this effect is quite modest, enhancing O2 delivery by about 5%. In a recent study by Rummer and colleagues in Science, they report that the unique Hb system present in fish can result in almost a 100% increase in O2 delivery, over 20-times that of air-breathing vertebrates. Oxygen delivery is crucial for metabolism and thus, life. Given that fish represent half of all vertebrates on the planet, and most fish possess some aspect of this system, this new discovery may shed insight into the evolution of one of the most successful groups of vertebrates; the fishes.
The paper "Root Effect Haemoglobin May Have Evolved to Enhance General Tissue Oxygen Delivery? by J.L. Rummer, D.J. McKenzie, A. Innocenti, C.T. Supuran, and C.J. Brauner, published in Science.
19 June 2013
FRIENDS COUNT WHEN LEARNING ABOUT RISK
Whether choosing a mate, deciding where to breed, selecting a foraging area or knowing who to avoid, an individual?s decisions can disclose useful information to others. A new study by research from James Cook University, lead by Rachel Manassa, has shown that watching others provides crutial information about predators for juvenile fishes setteling onto coral reefs.
Following a period of time spent developing in the open seas, away from coral reefs, juvenile fishes return to a world full of predators. However, at this time they cannot distinguish friends from foe and must learn who to avoid. Along with fellow researchers, Rachel Manassa demostrated that fishes were able to learn a predators identity by observing fish from of the same species and distantly related fish, that had already learned which species represented a threat.
"By using social information from other species individuals are likely to gain a significant survival advantage as the opportunity to acquire important information is increased. Given this, social learning is likely to play a vital role during critical life history transitions (e.g. settlement) where predation pressures are spatially and temporally unreliable ", says Rachel Manassa.
The paper "Socially acquired predator recognition in complex ecosystems" RP Manassa, MI McCormick and DP Chivers appears in Behavioural Ecology and Sociobiology (2013)
12 June 2013
SIZE COUNTS WHEN LEARNING ABOUT PREDATORS
Juvenile reef fish are not only able to learn about which predators are a risk using chemical cues released from other fish but they are able to choose who they learn from based on the size of the other fish.
The ultimate goal for all animals is to gain energy for growth so that they can reproduce and pass on their genes to the next generation. However, they must balance the need to acquire resources with avoiding be captured and eaten by other animals. Individuals that can best balance this tread-off will be the ones who succeed. Dr Matthew Mitchell and Prof Mark McCormick, from James Cook University and ARC Centre of Excellence for Coral Reef Studies, investigated how reef fishes are able to optimise this trade-off by selectively learning about predators and their risk using chemical cues in their environment.
?Fishes are surrounding by different cues that provide information about predation risk which they are able to access and modify their behaviour to optimise avoid being eaten in the most efficient way. Part of optimising the trade-off in behaviours is knowing which of these cues to respond to,? says Dr Mitchell.
One of the more important types of cue for risk assessment, are known as chemical alarm cues. These alarm cues are released from prey when they are captured by a predator and detection of these cues alerts other fish that there is a predator in the area. These cues can also be used to learn about predators and the risk the pose when fish see the predator or detect its odour at the same time as detecting the chemical alarm cue from another fish.
"Most predators are limited to targeting a specific size range of prey as they struggle to handle large prey and small prey offer little nutritionally. Consequently, cues from different sized fish should provide different information about which predators are in the local area."
To test this Dr Mitchell exposed fish to chemical alarm cues from different sized fish to see how they responded. ?Fish that were exposed to cues from similar sized fish displayed distinct anti-predator behaviours, such as increased vigilance; however fish exposed to cues from larger fish showed no change in their behaviour.?
To see if this difference in response to alarm cues had an effect on how fish learn about predators, fish were taught to recognise predator odours using alarm cues from small and large cues. Again, only fish taught with alarm cues from similar sized fish learnt to recognise the predator.
Dr Mitchell suggests that, while it may seem counterintuitive to ignore information about potential predators, being highly selective in how they learn prey fish are able to maximise their opportunities to feed and grow.
"Predation risk is not constant but fluctuates in time and space. Learning allows fish to adapt to changing environments and levels of risk as they grow and move. Such flexible behaviour is critical for survival?.
The finding of this study are reported in the paper ?Ontogenetic differences in chemical alarm cue production determine antipredator responses and learned predator recognition? Mitchell MD and MI McCormick, Behavioural Ecology and Sociobiology (2013)
6 June 2013
PAPER MAKES MOST CITED LIST FOR 2012
A recent study conducted by members of the Reef Fish Ecology Lab, JCU in collaboration with Dr Paolo Domenici has been listed the top 10 most citied articles in 2012 by the prestigious journal Biology Letters, which is part of the Royal Society of London Publishing Group.
The paper, citied by over 25 other research articles, investigated the effects of rising CO2 levels in oceanic waters on the lateralization of fish brains. Lateralization refers to the asymmetrical functioning of the brain; a process that allows higher brain functioning and results enhanced performance during cognitive tasks and behaviours. Generally, lateralised individuals have an advantage in multi-tasking and time minimization in decision-making. In humans lateralisation results in us being left or right handed. Similarly in fish, lateralisation results in fish showing a tendency to turn either left or right during an attack from a predator giving them a split second advantage.
The researchers found that when fish had been maintained in CO2 levels equivalent to those predicted to occur by the end of the century, the larvae lost their preference to turn left or right. Elevated CO2 disrupts this lateralization, to the extent that elevated-CO2 exposed fish showed no difference with random choice. Given the advantages of lateralization demonstrated in previous work, disruption of lateralization may be detrimental for the survival of larvae in elevated CO2. These results, together with previous work on sensory performance, points to an effect of elevated CO2 on a highly conserved element of nervous system function.
The paper "Elevated CO2 affects behavioral lateralization in a coral reef fish" Domenici P, Allan B, McCormick MI, Munday PL (2012) appears in Biology Letters 8
29 May 2013
FISH USE SOPHISTICATED MECHANISMS TO LEARN ABOUT PREDATORS
Recognising predators and respond appropriately is critical for all animals to survive to reproduce. While some species are able to innately recognise predators during their first encounters, many species must learn to recognise predators through experience. While this may seem surprising, as learning about predators means they must interact with the predator at some level during a predatory context, learning allows prey to maximise overall fitness through the accurate identification and assessment of risky situations. Recently, studies have demonstrated that prey are able to reduce the risk associated with learning about predators through a mechanism known as generalisation.
Generalisation allows individuals to use information gained through experience and apply it to similar novel situations. Thus, prey can mitigate some of the costs associated with learning predators individually by generalising recognition of one predator to other closely related novel predators that share similar characteristics. Theory suggests that the extent to which individuals generalise recognition depends on the ratio of predators to non-predators within a community. However, the capacity of prey to generalise recognition and distinguish between novel predators and non-predators is poorly understood, particularly in species-diverse communities with many closely related predators and non-predators. Fish assemblages on coral reefs not only maintain a high species diversity but a high trophic diversity. Costly mistakes can be made if prey misidentify non-predators as predators, raising the question of whether generalising recognition is beneficial.
A team of researchers from Australia and Canada, lead by Dr. Matt Mitchell, tested prey?s ability to generalise recognition of predators in a highly diverse environment where the ability to predict the identity of predators through generalisation is low. They first taught naive juvenile lemon damselfish to fear the smell of a predatory reef fish, the moon wrasse. Following this, they tested whether these fish could recognise that not only were moon wrasse a potential threat but whether they also recognised a range of closely related predators and non-predators as threats. They found that the damself fish not only recognised the moon wrasse as a threat but they were also able to use their experiance with moon wrasse to recognise other closely related species as a threat. Their findings suggest that fish are able to adjust how how many species they generalsise recognition to depending on the composition of fish community they are exposed to. learning about predation risks in this way allows fish to rapidly learn about risk in their environment and significantly enhances their chances of surviving in a new environment.
The teams latest paper "Generalization of learned predator recognition in coral reef ecosystems: how cautious are damselfish?" by Matthew Mitchell, Mark McCormick, Doug Chivers and Maud Ferrari appears in the journal Functional Ecology. Download PDF
| 16 January 2012 |  |
CARBON DIOXIDE IS 'DRIVING FISH CRAZY'
Rising human carbon dioxide emissions may be affecting the brains and central nervous system of sea fishes with serious consequences for their survival, an international scientific team has found.
Carbon dioxide concentrations predicted to occur in the ocean by the end of this century will interfere with fishes? ability to hear, smell, turn and evade predators, says Professor Phillip Munday of the ARC Centre of Excellence for Coral Reef Studies and James Cook University.
?For several years our team have been testing the performance of baby coral fishes in sea water containing higher levels of dissolved CO2 ? and it is now pretty clear that they sustain significant disruption to their central nervous system, which is likely to impair their chances of survival,? Prof. Munday says.
In their latest paper, published in the journal Nature Climate Change, Prof. Munday and colleagues report world-first evidence that high CO2 levels in sea water disrupts a key brain receptor in fish, causing marked changes in their behaviour and sensory ability.
?We?ve found that elevated CO2 in the oceans can directly interfere with fish neurotransmitter functions, which poses a direct and previously unknown threat to sea life,? Prof. Munday says.
Prof. Munday and his colleagues began by studying how baby clown and damsel fishes performed alongside their predators in CO2-enriched water. They found that, while the predators were somewhat affected, the baby fish suffered much higher rates of attrition.
?Our early work showed that the sense of smell of baby fish was harmed by higher CO2 in the water ? meaning they found it harder to locate a reef to settle on or detect the warning smell of a predator fish. But we suspected there was much more to it than the loss of ability to smell.?
The team then examined whether fishes? sense of hearing ? used to locate and home in on reefs at night, and avoid them during the day ? was affected. ?The answer is, yes it was. They were confused and no longer avoided reef sounds during the day. Being attracted to reefs during daylight would make them easy meat for predators.?
Other work showed the fish also tended to lose their natural instinct to turn left or right ? an important factor in schooling behaviour which also makes them more vulnerable, as lone fish are easily eaten by predators.
?All this led us to suspect it wasn?t simply damage to their individual senses that was going on ? but rather, that higher levels of carbon dioxide were affecting their whole central nervous system.?
The team?s latest research shows that high CO2 directly stimulates a receptor in the fish brain called GABA-A, leading to a reversal in its normal function and over-excitement of certain nerve signals.
While most animals with brains have GABA-A receptors, the team considers the effects of elevated CO2 are likely to be most felt by those living in water, as they have lower blood CO2 levels normally. The main impact is likely to be felt by some crustaceans and by most fishes, especially those which use a lot of oxygen.
Prof. Munday said that around 2.3 billion tonnes of human CO2 emissions dissolve into the world?s oceans every year, causing changes in the chemical environment of the water in which fish and other species live.
?We?ve now established it isn?t simply the acidification of the oceans that is causing disruption ? as is the case with shellfish and plankton with chalky skeletons ? but the actual dissolved CO2 itself is damaging the fishes? nervous systems.?
The work shows that fish with high oxygen consumption are likely to be most affected, suggesting the effects of high CO2 may impair some species worse than others ? possibly including important species targeted by the world?s fishing industries.
The team?s latest paper ?Near-future CO2 levels alter fish behaviour by interfering with neurotransmitter function? by Göran E. Nilsson, Danielle L. Dixson, Paolo Domenici, Mark I. McCormick, Christina Sřrensen, Sue-Ann Watson, and Philip L. Munday appears in the journal Nature Climate Change.
More information:
CoECRS are proud sponsors of the 12th International Coral Reef Symposium, Cairns: 9-13 July 2012.
| 5 December 2011 | |
WHEN THE HEAT?S ON, FISH CAN COPE
Australian scientists have discovered that some tropical fish have a greater capacity to cope with rising sea temperatures than previously thought ? by adjusting over several generations.
The discovery, by researchers at the ARC Centre of Excellence in Coral Reef Studies, James Cook University and CSIRO sheds a ray of hope amid the rising concern over the future of coral reefs and their fish under the levels of global warming expected to occur by the end of the 21st century.
Understanding the ability of species to acclimatise to rising temperatures over longer time periods is critical for predicting the biological consequences of global warming - yet it remains one of the least understood aspects of climate science. The scientists were seeking to discover how fish would cope with the elevated sea temperatures expected by 2050 and 2100.
?When we exposed damsel fish to water temperatures 1.5 degrees and 3 degrees above today?s, there was a marked decline in their aerobic capacity as we?d expected,? explains lead researcher Jennifer Donelson. ?This affects their ability to swim fast and avoid predators.?
?However when we bred the fish for several generations at higher temperatures, we found that the second generation offspring had almost completely adjusted to the higher temperatures. We were amazed? stunned, even,? she says. ?It shows that some species can adjust faster than the rate of climate change.?
?When one generation of damselfish experiences high temperatures their whole life, the next generation is better able to cope with warmer water. We don?t yet fully understand the mechanisms involved, but it doesn?t seem to be simple Darwinian selection over a couple of generations,? explains team leader Professor Philip Munday.
?Instead, there has been a transmission of information between the generations that enables damselfish to adjust to higher water temperatures.?
The two temperatures used in the trial represent likely tropical ocean temperatures at the mid-century and by 2100, based on current trends in carbon dioxide emissions by humanity. A 3 degree increase in tropical ocean temperatures, is the temperature predicted to occur if humanity?s carbon dioxide emission continue on their current trajectory.
The unusual finding suggests that some fish may have an innate ability to cope with increased sea temperatures greater than previously thought, the researchers say.
However they caution it applies so far only to a single coral reef fish species, and does not address the more complex issue of the survival of the coral habitat itself, and the effects of warming on plankton in the food chains on which fish depend.
Also, there are likely to be penalties for fish that successfully adapt to higher temperatures, Jennifer Donelson says. Initial observations suggest that the acclimatized offspring are on average smaller than their parents, and we still do not know if they are able to reproduce at the same rate as their predecessors.
Although the experiment has yet to run its full course, the researchers also say they do not expect the fishes? ability to adjust to higher temperatures to continue past 3 degrees.
?At such a level of planetary warming there will be profound changes in Earth?s ecosystems, affecting all forms of life, including humans,? says Prof. Munday.
However, assuming humans manage to gradually bring global warming under control, it is important to understand how well animals and plants can cope with higher temperatures, in order to manage ecosystems for optimum survival of their species and the services they provide. This research provides an early insight into the adaptive capacity of fish, the team says.
This study reveals that transgenerational acclimation is a potentially important mechanism for coping with rapid climate change. Such acclimation could reduce the impact of warming temperatures and allow some fish populations to persist across their current range, instead of having to move away in search of cooler waters.
Their paper ?Rapid transgenerational acclimation of a tropical reef fish to climate change? by J. M. Donelson, P. L. Munday, M. I. McCormick and C. R. Pitcher, appears in the latest issue of the journal Nature Climate Change.
More information:
CoECRS are proud sponsors of the 12th International Coral Reef Symposium, Cairns: 9-13 July 2012.
Click here for pdf
Click here for Electronic Supplementary.pdf
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| July 2010 | |
CARBON EMISSIONS THREATEN FISH POPULATIONS
Humanity?s rising CO2 emissions could have a significant impact on the world?s fish populations according to groundbreaking new research carried out in Australia.
Baby fish may become easy meat for predators as the world?s oceans become more acidic due to CO2 fallout from human activity, an international team of researchers has discovered.
In a series of experiments reported in the latest issue of the Proceedings of the National Academy of Science (PNAS), the team found that as carbon levels rise and ocean water acidifies, the behaviour of baby fish changes dramatically ? in ways that decrease their chances of survival by 500 to 800 per cent.
?As CO2 increases in the atmosphere and dissolves into the oceans, the water becomes slightly more acidic. Eventually this reaches a point where it significantly changes the sense of smell and behaviour of larval fish,? says team leader Professor Philip Munday of the Australian Research Council?s Centre of Excellence for Coral Reef Studies (CoECRS) at James Cook University.
?Instead of avoiding predators, they become attracted to them. They appear to lose their natural caution and start taking big risks, such as swimming out in the open - with lethal consequences.?
Professor Mark McCormick, a co-author on the paper, says the change in fish behaviour could have serious implications for the sustainability of fish populations because fewer baby fish will survive to replenish adult populations.
?Every time we start a car or turn on the light part of the resulting CO2 is absorbed by the oceans, turning them slightly more acidic. Ocean pH has already declined by 0.1 unit and could fall a further 03.-0.4 of a unit if we continue to emit CO2 at our present increasing rate.
?We already know this will have an adverse effect on corals, shellfish, plankton and other organisms with calcified skeletons. Now we are starting to find it could affect other marine life, such as fish.?
Earlier research by Professor Munday and colleagues found that baby ?Nemo? clownfish were unable to find their way back to their home reef under more acidic conditions. The latest experiments cover a wider range of fish species and show that acidified sea water produces dangerous changes in fish behaviour.
?If humanity keeps on burning coal and oil at current rates, atmospheric CO2 levels will be 750-1000 parts per million by the end of the century. This will acidify the seas at least 100 times faster than has happened at any stage in the last 650,000 years.
?In our experiments we created the kind of sea water we will have in the latter part of this century if we do nothing to reduce emissions. We exposed baby fish to it, in an aquarium and then returned some to the sea to see how they behaved.
?When we released them on the reef, we found that they swam further away from shelter and their mortality rates were five to eight times higher than those of normal baby fish,? Professor Munday says.
He adds it should be clearly understood that this impact is likely to happen independent of global warming, and is a direct consequence of human carbon emissions.
The research team concludes ?Our results demonstrate that additional CO2 absorbed into the ocean will reduce recruitment success and have far-reaching consequences for the sustainability of fish populations.?
Professor Munday adds ?In its 2008 report on the state of the world?s fisheries the UN Food and Agriculture Organization said ?the maximum wild capture fisheries potential from the world?s oceans has probably been reached?. If you add the impact of ocean acidification and other climate change impacts to this, it means there are grounds for serious concern about the future state of world fish stocks and the amount of food we will be able to obtain from the sea.?
The article ?Replenishment of fish populations is threatened by ocean acidification? by
Philip L. Munday, Danielle L. Dixson, Mark I. McCormick, Mark Meekan, Maud
C.O. Ferrari and Douglas P. Chivers appears in the latest issue of PNAS 107:12930-12934
Click here for pdf
More information:
| November 3, 2009 |
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Bullies evict little fish as the reef warms
Small fish are at risk of being bullied to death by big ones as coral reef resources are hit by climate change.
The finding from new research by a scientist at the ARC Centre of Excellence for Coral Reef Studies (CoECRS) has serious implications for both fishing and reef-based tourism industries.
In the battle to survive on severely bleached corals, large damselfish push smaller ones further from the limited shelter and resources, exposing them to predators that snap them up, the study by Associate Professor Mark McCormick of CoECRS and James Cook University finds.
?Juvenile damselfish living on bleached or dead corals are four times more likely to die than those living on healthy coral,? Prof. McCormick says.
?We knew that coral bleaching events were causing an increase in fish deaths, but this is the first study to reveal the behavioural mechanism that is driving this mortality,? he says.
?On healthy coral, juvenile damselfish of all sizes have an equal chance of dying, but on bleached coral, it?s every fish for themselves and death rates are much higher among the runts,? he adds.
?The results were surprising, as these damselfish are known to use a broad range of habitats. They are found living on dead coral, rubble and live coral so we didn?t think that coral bleaching would have such a dramatic affect on their mortality. We would expect even more striking impacts on fishes that have a closer association with live coral. ?
?Coral bleaching is predicted by scientists to increase in frequency and severity as ocean temperatures rise due to global warming. Since damselfish are prey for many large fish on the Great Barrier Reef, the behavioural changes could have far-reaching effects,? says Prof. McCormick.
A decline in the number of small fish that live on reefs, means lower numbers of the predatory fishes that eat them ? and these are the fish we commonly harvest, like coral trout, he warns.
In order to understand why mortality was increasing, Prof. McCormick placed juvenile damselfish on healthy, bleached and dead corals on the Great Barrier Reef.
He found that fish stayed closer to shelter on live coral, while on bleached and dead coral they moved higher up the coral making them more vulnerable to predation, with the smaller ones being pushed right into open water.
The study also revealed that where damselfish settle at the end of their larval phase plays a crucial role in their survival. ?I expected that if fish settled on a bleached or dead coral they would soon move to a healthy one, but this turned out not to be the case,? says Prof. McCormick.
?Even when the damselfish were only 40 cm away from healthy, live coral with fewer inhabitants, they avoided moving. So their initial choice of habitat is key to their subsequent survival.?
Compounding the problem is the fact that most fish reach the end of their larval stage during the hottest months of the year, when coral is particularly vulnerable to bleaching. This timing means that a large number of juveniles are likely to settle onto live coral that may subsequently bleach. The different behaviour they exhibit on bleached coral means that virtually all will die, according to Prof. McCormick.
?Those that do manage to survive in degraded habitats will have different body characteristics than those who survive on live coral. The results suggest that if widespread bleaching occurs we may expect to see changes in the characteristics of juveniles ? for example, it may be advantageous to settle larger. The natural balance between the number of fish that die as larvae and the number that die when they reach the reef may also be disrupted.? he adds.
The only way to reduce the effect of coral bleaching on fish communities is to make the system more resilient, said Prof. McCormick.
?If we take away the stress of harvesting and pollution caused directly by human activities, the habitat may be better able to resist the stress of increased water temperature and the community may be able to bounce back more quickly from major environmental change.?
The paper, ?Behaviourally Mediated Phenotypic Selection in a Disturbed Coral Reef Environment?, by
Mark I. McCormick was published in PLoS ONE on Friday 18 September. Click for article
More information:
Assoc Prof Mark McCormick, CoECRS and JCU +61 (0)7 4781 4048 or
Jenny Lappin, CoECRS, +61 (0)7 4781 4222
Jim O?Brien, James Cook University Media Office, 07 4781 4822 or 0418 892449
http://www.coralcoe.org.au/
Captions:
Top. The ambon damselfish (Pomacentrus amboinensis) is a habitat generalist but despite this juvenile survival was four times lower on bleaching coral compared to healthy coral.
Mid. Coral reefs are the most biologically diverse ecosystems on the planet, but this diversity is now threatened by climate driven change.
Bottom. Higher mortality on bleached coral is in part due to the fish's greater visibility against bleached coral making them more vulnerable to predators.
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April 2009
Baby fish shaped by mothers? stress
Stressed reef fish mothers produce highly active babies, and this affects survival and has important implications for fish populations in a changing environment, according to new research.
Dr Monica Gagliano, a research fellow with the AIMS@JCU joint venture, worked with colleague Dr Mark McCormick from the ARC Centre of Excellence for Coral Reef Studies (James Cook University) on a study that deepens our understanding of how stress affects the dynamics of wild fish populations and hence how fish may cope with increasing human-induced stresses.
This work, published today in the journal Oecologia*, has implications for management of fisheries resources as well as increasing our knowledge of the basic physiological processes governing the life cycles of fish.
Dr Gagliano and Dr McCormick have shown that the parental environment of a common reef species, Ambon damsel fish, is crucial for the future lives of their offspring. In their laboratory research, they determined the effects of maternal stress on offspring characteristics by exposing fertilised fish eggs gathered from the wild to different levels of the stress hormone cortisol.
?These baby fish can?t make these important hormones until later in life, so their whole initial development is determined by hormones they obtain from their mothers,? Dr McCormick said.
Previous studies had shown that females of this species release cortisol from their ovaries in response to environmental stress; those fish in isolated reefs with few predators or competitors show low levels of the hormone while those in high stress environments bathe their eggs in high levels of the hormone. The present study shows just what all that stress hormone can do to the eggs.
?If the mother fish is more stressed and she passes on more cortisol, then the offspring will have a faster developmental rhythm and therefore errors will be more likely in their development. One likely result of this is that the offspring are born asymmetrical,? Dr Gagliano said.
Research published in 2008 by Dr Gagliano and colleagues showed that fish born with asymmetrical ear bones (otoliths) face huge problems negotiating the open ocean stage of their development, and many are lost of sea before they can settle on a reef to breed. Their asymmetry interfered with their hearing, making it hard from them to home in on reef-related sounds.
Recent work by Ms Tove Lemberget at JCU, with Dr McCormick, also published in Oecologia, found that asymmetry of the larval stages was strongly related to survival in Caribbean lizardfishes (see Lemberget and McCormick 2009, ?Replenishment success linked to fluctuating asymmetry in larval fish? ref below **).
Dr Gagliano?s latest research also shows that stress, in this case maternal stress, has a large measurable effect on the shape of the ear bones, with those baby fish receiving the high dose of cortisol being more than twice as likely to have asymmetrical ear bones compared with those that received none.
Together, this research suggests that stressed mothers produce offspring that are much less likely to survive. Mothers in healthy, low stress environments are likely to contribute most to the next generation.
*The Oecologia paper is titled ?Hormonally-mediated maternal effects shape offspring survival potential in stressful environments?. Oecologia
**Lemberget T, McCormick MI (2009) Replenishment success linked to fluctuating asymmetry in larval fish. Oecologia 159:8-93
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| 2 December, 2008 | |
Fish Have Sexy Ears
You can tell when a fish has changed sex just by looking at its ears.
At least, Australian marine biologists Stefan Walker and Mark McCormick can ? having just pioneered a new breakthrough for studying the behaviour and productivity of fish populations.
The researchers from the ARC Centre of Excellence for Coral Reef Studies and James Cook University have solved one of the major problems confronting fisheries biologists in determining the sustainability of fish populations ? not knowing exactly when fish undergo a sex change.
?Many coral reef fishes - and other fish like barramundi - undergo a sex change at some point in their life ? from male to female or female to male,? Stefan explains. ?This may be good breeding strategy for them, but it makes it very difficult for researchers to assess the productivity of the fish population if we don?t know for sure when the sex change takes place.?
With almost a third of world fisheries rated as having collapsed and many more under threat, and with coral reefs facing climate and other human-caused stresses, it is vital to assess the productivity of fish populations in order to know how much fishing pressure it can withstand and whether or not it can bounce back. This includes having an understanding of the gender ratios and the age at maturity for females and males.
?Unfortunately in fish that change sex this is hard to get a handle on, because the change can happen at different times. We needed a tool that would tell with accuracy when sex change has taken place or is likely to occur,? he says.
The team decided to focus on the fishes? ear stones, or otoliths, which develop through the deposition of daily layers, providing an age-based history of the individual?s growth. They proposed that the process of sex change may effect otolith growth, resulting in formation of an age-specific sex-change signature. To their delight they found a dense region in the otolith material that corresponded exactly with the time when their subject fish ? a small reef perch ? changed from female to male.
Furthermore as soon as the new males acquired a harem of females, their ear-stones began to grow much more rapidly and in a different direction than when they were females. And the more females they had, the faster and larger their ?ears? grew.
This new information about sex change and otolith development can help fisheries scientists to more accurately assess the dynamics and productivity of hermaphroditic stocks, the researchers say.
?The sex-change associated otolith signature allows patterns of sex-change and sex-specific growth to be investigated at the individual level. We can now determine the relative amount of time individuals spend as female and male, and how this ratio varies, both naturally and in response to fishing pressure.?
The researchers also have a theory that the larger and different shaped ear-stones in male perches may have something to do with the fine tuning of the fishes? spatial perception. Like humans, the inner ears of fish are not only receptive to sound, but are also receptive to individual movement and orientation. Sex changing fish may also change their otolith development so as to become more proficient in their new reproductive mode, which often involves moving around more complex terrain and engaging in physical combat with other males associated with competition for female partners. They intend to test this idea in subsequent research.
Their paper Fish ears are sensitive to sex-change is in Biology Letters of the Royal Society
More information:
| The sand perch, Parapercis cylindrica, like most coral reef fishes change sex from female to male and live in complex social groups. Interestingly, the formation of the stones that allow them to hear and give them balance record when they change sex. |  |