Imagine you are a fish. You are a baby barramundi. You are happily drifting along the Great Barrier Reef coastline, pushed by the current.
You grow fast, and when you are about two weeks old your instincts tell you that it’s time to move to the place where grown-up fish live. It’s time to go to the mangroves.
But then something goes wrong.
Published today in the journal Proceedings of the Royal Society B, new research from the University of Adelaide suggests that climate change will reduce the number of baby fish that make it to adulthood.
The study indicates that increased atmospheric carbon dioxide could have an impact through altering the behaviour of juvenile fish, leading to poorer chances of survival.
“After hatching in the open ocean, baby fish travel to reefs or mangroves as safe places to feed and grow into adults,” explained Tullio Rossi, lead author on the study and PhD candidate at The Environment Institute, University of Adelaide.
“But when ocean acidity increases due to higher dissolved carbon dioxide, a number of factors reduce the chance of fish actually finding those safe havens.”
Tullio’s study focused on barramundi, a tropical fish whose range extends from the eastern Indian Ocean to the western Central Pacific. The species is highly valued across fisheries production, tourism and aquaculture industries.
In Australia, commercial barramundi fisheries produce around 5000 tonnes per annum, with an estimated production value of around AU$45 million.
“Wild barramundi migrate from fresh water to the ocean to spawn, with eggs and freshly hatched fish typically found around river mouths and marine bays,” said Tullio.
“At around two weeks of age, juvenile barramundi settle into mangroves and wetland habitats.”
But how do they know where to go? By listening.
Snapping shrimp and other creatures living in mangroves produce an underwater ruckus the fish are able to hear and follow.
Tullio’s research showed that when barramundi hatch and grow under conditions of elevated carbon dioxide, their response to mangrove sound is changed from attraction to avoidance. The study conditions were designed to reflect carbon dioxide levels expected by the end of this century at the current rate of carbon emissions.
“Our results show that ocean acidification can disrupt the window of opportunity for sound-driven orientation by baby barramundi towards settlement habitats,” said Tullio.
“This could lead to decreased chances of finding suitable adult habitat, leaving fish exposed to predation and starvation for longer periods of time.”
The study also found that even if they do find suitable shelter, baby barramundi exposed to elevated carbon dioxide are then inclined to remain hidden more than normal. From an ecological perspective, this might result in decreased success in finding food.
The scientists believe that increased ocean acidity changes how fish process sensory information via neurotransmitters, creating striking and dangerous alterations in their behaviour.
“If we continue to burn fossil fuels at current levels we could put baby fish in serious trouble, ultimately leaving them lost in an acidified ocean,” says Tullio.
“And this would inevitably lead to fewer adult fish and, potentially, reduced stocks for the fisheries we depend on for food.”
But it’s not too late.
“The good news is that we are still in time to limit our carbon emissions to levels that are not too dangerous for marine animals,” said Tullio.
Signed by 196 nations, The Paris Agreement was reached on December 12 2015, and commits nations to a timetable of emissions reductions aimed at keeping temperatures ‘well below 2°C above pre-industrial levels and to pursue efforts to limit the temperature increase to 1.5°C.’
Tullio Rossi performed this study in collaboration with Professor Sean Connell (University of Adelaide), Dr Stephen Simpson (University of Exeter) and Professor Philip Munday (James Cook University).
Tullio is also a passionate science communicator, running the Ocean Acidification Page on Facebook and creating animations communicate his research findings.
Tullio presented his research at Fresh Science South Australia 2015.
Fresh Science is a national program that helps early-career researchers find and share their stories of discovery.
Tullio Rossi, University of Adelaide
Phone: +61 8 8313 0543