Recent Media Releases
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.
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Professor Mark McCormick, (0409 371015), email@example.com
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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.
Oona Lönnstedt, School of Marine & Tropical Biology, James Cook University, ph +46 700 21 83 46
Professor Mark McCormick, School of Marine & Tropical Biology, James Cook University, +61 7 4781 4048 or 0409 371 015
Jim O’Brien, James Cook University Media Office, +61 (0)7 4781 4822 or 0418 892449
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
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 340:1327-1329. Download PDF
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) 67: 1033-1040. Download PDF
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) 67:1123-1129. Download PDF
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 8:70-81. Download PDF.
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 Sørensen, Sue-Ann Watson, and Philip L. Munday appears in the journal Nature Climate Change.
Prof. Phillip Munday, CoECRS and JCU, ph +61 (0)7 47815341 or 0408 714 794
Dr Sue-Ann Watson, CoECRS, ph 0419 422 815;
Prof. Mark McCormick, CoECRS and JCU, ph +61 (0)7 47814048 or 0409 371 015
Jenny Lappin, CoECRS, ph 0417 741 638
Jim O’Brien, James Cook University Media Office, +61 (0)7 4781 4822 or 0418 892449
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.
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.
Jennifer Donelson, CoECRS and JCU, +61 (0)419 422 815
Prof. Philip Munday, CoECRS and JCU, ph +61 (0)7 47815341 or +61 (0)408 714 794
Prof. Mark McCormick, CoECRS and JCU, ph +61 (0)7 4781 4048 or 0409 371 015
Jenny Lappin, CoECRS, +61 (0)7 4781 4222
Jim O’Brien, James Cook University Media Office, +61 (0)7 4781 4822 or 0418 892449
CoECRS are proud sponsors of the 12th International Coral Reef Symposium, Cairns: 9-13 July 2012.
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
Professor Philip Munday, CoECRS and JCU, +61 (0)7 47815341 or 0431 036 393
Associate Professor Mark McCormick, CoECRS and JCU, +61 (0) 7 47814048 or 0408 008 246
Jenny Lappin, CoECRS, 07 4781 4222
Jim O’Brien, James Cook University Media Office, 07 4781 4822 or 0418 892449
|November 3, 2009
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
Assoc Prof Mark McCormick, CoECRS and JCU +61 (0)7 4781 4048 or 0408 008 246
Jenny Lappin, CoECRS, +61 (0)7 4781 4222
Jim O’Brien, James Cook University Media Office, 07 4781 4822 or 0418 892449
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.
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 160:657-665 Click for PDF Sup Figure
**Lemberget T, McCormick MI (2009) Replenishment success linked to fluctuating asymmetry in larval fish. Oecologia 159:8-93 Click for PDF
For further information, please contact:
Assoc Prof Mark McCormick: 07 4781 4048, firstname.lastname@example.org
Dr Monica Gagliano: 08 6369 4028, email@example.com
Ms Wendy Ellery: 07 4753 4409; 0418 729 265, firstname.lastname@example.org
|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 5: 73-76. Click for PDF
Stefan Walker, CoECRS and JCU, 0419 422 815, 61 (0)7 4781 5775
Mark McCormick, COECRS and JCU, +61 (0)7 4781 4048
Jenny Lappin, CoECRS, + 61 (0)7 4781 4222
Jim O’Brien, James Cook University Media Office, 61 (0)7 4781 4822
|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.|
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