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

One of Australia’s leading coral reef ecologists fears that reef biodiversity may not provide the level of insurance for ecosystem survival that we once thought.

In an international study published today, Professor David Bellwood from the ARC Centre of Excellence for Coral Reef Studies (Coral CoE) says we need to identify and protect the most important species within reef ecosystems.

In coral reefs, just as in any modern-day society, there are vital jobs that keep the ecosystem safe and functioning.

Professor Bellwood says, in many cases, a single species of fish carries out a unique and essential role, making the ecosystem vulnerable to loss of that species.

Professor Bellwood and a team of international colleagues, led by Professor David Mouillot from the University of Montpellier, examined the ‘jobs’ of over six thousand coral reef fish species across 169 locations worldwide.

“What we often assume is that if we lose one species on a reef, there are many others that can step in and take over their job,” Professor Bellwood explains.

But he and his colleagues fear that’s not the case. They believe if a reef ecosystem were to lose a species that carried out a ‘specialist’ role, the impact could be profound.

“We could easily lose a type of fish that has no substitute, no replacement,” Professor Bellwood says.

“Unfortunately we have become complacent, we have assumed that biodiversity will buy us some time and give us some insurance, but that’s not necessarily the case.”

“It’s not about numbers of species,” adds Professor David Mouillot. “Biodiversity is important and desirable in an ecosystem, but it is not necessarily the key to being safe and secure”.

Professor Bellwood singles out the parrotfish, explaining that out of thousands of reef fish species, on the Great Barrier Reef only one parrotfish species regularly performs the task of scraping and cleaning inshore coral reefs.

“This parrotfish is a particularly valuable species,” he says, likening this finding to a large city with many inhabitants, but only one doctor.

“To protect ecosystems, we need to ensure that specific jobs are maintained,” Professor Bellwood says. “And that means we must protect the fish that do them.”

PAPER

‘Functional over-redundancy and high functional vulnerability in global fish faunas on tropical reefs’ by David Mouillot, Sébastien Villéger, Valeriano Parravicini, Michel Kulbicki, Jesus Ernesto Arias-González, Mariana Bender, Pascale Chabanet, Sergio R. Floeter, Alan Friedlander, Laurent Vigliola, and David R. Bellwood appears in Proceedings of the National Academy of Sciences.

The paper is available on request.

CONTACTS:

Professor David Bellwood, Coral CoE: +44 (0) 7901 236 784, or
+61 (0) 407 175 007, david.bellwood@jcu.edu.au
(David Bellwood is travelling in the UK and is contactable on the above number between 1630 – 0600 AEST daily)

Eleanor Gregory, Communications Manager Coral CoE: +61 (0) 7  4781 6067,
0428 785 895 eleanor.gregory@jcu.edu.au

Professor David Mouillot, University of Montpellier: +33 (0) 46 714 3719
david.mouillot@univ-montp2.fr