A new study suggests sharks will need to adapt, move or die as climate change could soon render their nurseries uninhabitable.

Baby sharks rely on coastal nursery-like spaces such as shallow lagoons and mangroves for food as well as protection from predators. But they also need to be robust enough to cope with the challenging conditions these environments throw at them—conditions that may soon become unbearable in a warming world.

“In shallow coastal habitats, baby sharks already have to tolerate the strain of high temperatures,” said the study’s lead author Dr Ian Bouyoucos, from the ARC Centre of Excellence for Coral Reef Studies at James Cook University (Coral CoE at JCU).

“The temperatures can also fluctuate dramatically on a daily basis. It’s the constant change that makes these environments ‘extreme’.”

Dr Bouyoucos said nursery areas are important for sustaining the local shark populations by serving as ‘safe havens’ for newborns and juveniles to learn critical survival and foraging skills. But the impacts of climate change are increasingly becoming a problem for their survival.

“We don’t know if sharks can adapt and can continue to use these important habitats early in life, or whether they will be able to find new nurseries, or whether populations will die off” he said.

Co-author Associate Professor Jodie Rummer, also from Coral CoE at JCU, says this is a case of adapt, move or die.

“Heatwaves due to climate change are becoming more frequent and severe, and lasting longer with climate change,” Dr Rummer said.

She said more work is needed to find current tolerance limits for newborn sharks to survive and thrive in shallow, warm nursery habitats.

“The temperature thresholds that limit their performance today can help us predict how future populations might fare as the waters continue to warm with climate change,” she said.

“But adaptation—changes in DNA over generations to accommodate new conditions—may not be possible. This is because sharks are slow to reach sexual maturity compared to most other fishes and do not reproduce as often or have as many babies. Therefore, not enough generations can go by fast enough to keep pace with the rate at which we—humans—are changing their habitats.”

Dr Rummer said there was a possibility newborn sharks could move to new nursery-like areas that are not as warm.

“Or, we might just see these shark populations disappear,” she said.

“This is a real risk. We know sharks are tolerating a lot already. The oceans, their habitats, are getting warmer, lower in oxygen, and lower in pH with climate change.”

As predators, sharks are essential for healthy ocean ecosystems. Without predators, whole ecosystems can collapse.

“We need to keep studying and protecting sharks,” Dr Bouyoucos said.

“Our sharks, ecosystems, and our futures all depend on us urgently cutting greenhouse gas emissions to curb climate change.”

PAPER

Bouyoucos I, Simpfendorfer C, Planes S, Schwieterman G, Weideli O, Rummer J. 2022. ‘Thermally insensitive physiological performance allows neonatal sharks to use coastal habitats as nursery areas’. Marine Ecology Progress Series. DOI: 10.3354/meps13941

IMAGES

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CONTACT

Ian Bouyoucos (Manitoba, CST)
E: ian.bouyoucos@umanitoba.ca

Jodie Rummer (Townsville, AEST)
P: +61 (0)439 166 171
E: jodie.rummer@jcu.edu.au

A shark’s habitat can reduce its sensitivity to rising CO₂ levels, according to Australian scientists.

Globally, ocean acidification – linked to emissions of greenhouse gases – remains a major concern and scientists say it will harm many marine species over the next century.

Researchers from the ARC Centre of Excellence for Coral Reef Studies (Coral CoE) at James Cook University have found that the epaulette shark, a species that shelters within reefs and copes with low oxygen levels, is able to tolerate increased carbon dioxide in the water without any obvious physical impact.

“As part of the study we exposed the sharks to increased CO₂ for more than two months, mirroring the levels predicted for the end of the century,” says study co-author Dr Jodie Rummer from Coral CoE.

“We then tested the sharks’ respiratory system, measuring how much oxygen it needed to maintain basic function under the experimental conditions.”

The researchers found the sharks were regulating their systems to counter the higher levels of acid in their bodies. Importantly, Dr Rummer explains, the sharks’ ability to cope with low oxygen levels – similar to that found in its natural habitat – was unaffected by high CO2 levels.

Study co-author, Professor Philip Munday from the Coral CoE says the sharks’ physiological adaptations, which enables it to cope with the conditions within reefs, makes them better able to tolerate ocean acidification.

“Species that live in shallow reef environments, where they can experience naturally high CO₂ levels on a regular basis, may have adaptations that make them more tolerant to future rises in CO₂ levels than other species.”

Professor Munday says the next critical step is to test the sensitivity of other shark species to ocean acidification.

“Species that live in the open ocean may be more susceptible to future acidification than those that naturally live in shallow reef environments where they already experience a variable environment.”

Dr Rummer adds that by determining which animals are more and less susceptible to high CO₂ than others, scientists will be better able to predict the future consequences of ocean acidification on marine ecosystems.

Paper

A product of its environment: The epaulette shark (Hemiscyllium) exhibits physiological tolerance to elevated environmental CO₂ by Dennis D.U Heinrich, Jodie Rummer, Andrea J. Morash, Sue-Ann Watson, Colin A. Simpfendorfer, Michelle R Heupel and Philip L. Munday is published in the journal Conservation Physiology.

Link to paper: http://conphys.oxfordjournals.org/content/2/1/cou047.full

Images

Epaulette shark sheltering in reef – image credit: M.Heupel.

Contact

Dr Jodie Rummer, Coral CoE – +61 7 4781 5300, +61 (0) 439 166 171
jodie.rummer@jcu.edu.au

Professor Philip Munday, Coral CoE – +61 7 4781 5341
philip.munday@jcu.edu.au

Eleanor Gregory, Coral CoE Media – +61 (0) 428 785 895
eleanor.gregory@jcu.edu.au