16th May 2016
Stinky bleached coral stops reef fish from identifying predators
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.
McCormick M.I., Lönnstedt O.M. 2016 Disrupted learning: habitat degradation impairs crucial antipredator responses in naïve prey. Proceedings of the Royal Society B 20160441. (doi:10.1098/rspb.2016.0441).
Professor Mark McCormick, ARC Centre of Excellence for Coral Reef Studies, James Cook University
Mobile: +61 (0) 409 371 015
Dr Oona Lönnstedt, University of Uppsala
Mobile: +46 700 218346
Coral bleaching is currently a major cause of coral death and ecosystem degradation (Photo credit: Bridie Allan)
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
Tiny fish make ‘eyes’ at their killer
Small prey fish can grow a bigger ‘eye’ on their rear fins as a way of distracting predators and dramatically boosting their chances of survival, new scientific research has found.
Researchers from Australia’s ARC Centre of Excellence for Coral Reef Studies (CoECRS) have made a world-first discovery that, when constantly threatened with being eaten, small damsel fish not only grow a larger false ‘eye spot’ near their tail – but also reduce the size of their real eyes.
The result is a fish that looks like it is heading in the opposite direction – potentially confusing predatory fish with plans to gobble them up, says Oona Lönnstedt, a graduate student at CoECRS and James Cook University.
For decades scientists have debated whether false eyespots, or dark circular marks on less vulnerable regions of the bodies of prey animals, played an important role in protecting them from predators – or were simply a fortuitous evolutionary accident.
The CoECRS team has found the first clear evidence that fish can change the size of both the misleading spot and their real eye to maximise their chances of survival when under threat.
“It’s an amazing feat of cunning for a tiny fish,” Ms Lonnstedt says. “Young damsel fish are pale yellow in colour and have this distinctive black circular ‘eye’ marking towards their tail, which fades as they mature. We figured it must serve an important purpose when they are young.”
“We found that when young damsel fish were placed in a specially built tank where they could see and smell predatory fish without being attacked, they automatically began to grow a bigger eye spot, and their real eye became relatively smaller, compared with damsels exposed only to herbivorous fish, or isolated ones.
“We believe this is the first study to document predator-induced changes in the size of eyes and eye-spots in prey animals.”
When the researchers investigated what happens in nature on a coral reef with lots of predators, they found that juvenile damsel fish with enlarged eye spots had an amazing five times the survival rate of fish with a normal-sized spot.
“This was dramatic proof that eyespots work – and give young fish a hugely increased chance of not being eaten.
“We think the eyespots not only cause the predator to attack the wrong end of the fish, enabling it to escape by accelerating in the opposite direction, but also reduce the risk of fatal injury to the head,” she explains.
The team also noted that when placed in proximity to a predator the young damsel fish also adopted other protective behaviours and features, including reducing activity levels, taking refuge more often and developing a chunkier body shape less easy for a predator to swallow.
“It all goes to show that even a very young, tiny fish a few millimetres long have evolved quite a range of clever strategies for survival which they can deploy when a threatening situation demands,” Ms Lonnstedt says.
Their paper “Predator-induced changes in the growth of eyes and false eyespots by Oona M. Lonnstedt, Mark I. McCormick and Douglas P. Chivers appears in the latest issue of the journal Scientific reports. click here for paper
Oona Lonnstedt, CoECRS and JCU, ph +646 700 21 83 46
Dr Mark McCormick, CoECRS and JCU +61 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
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