Coral ‘helper’ stays robust under ocean acidification

Scientists say a type of algae crucial to the survival of coral reefs may be able to resist the impacts of ocean acidification caused by climate change.

In a world-first, the team—including researchers from the ARC Centre of Excellence for Coral Reef Studies at The University of Western Australia (Coral CoE at UWA)—found that coralline algae are able to build tolerance to ocean acidification over multiple generations.

“Coralline algae go through a natural process of calcification, where they build a crustose-like calcium carbonate skeleton,” said lead author Dr Christopher Cornwall.

“Skeletons like this provide structure, allowing them to grow, as well as providing a substrate for other organisms such as corals to grow upon,” he said.

“We show, for the first time, that while growth of these skeletons is initially susceptible to the effects of ocean acidification caused by increased CO₂, over multiple generations they develop resistance.”

Coralline algae are vital not only to the survival of coral reefs but many ocean species.

“Crustose coralline algae bind coral reefs together,” said Professor McCulloch, Coral CoE Deputy Director, who led the research group. “Without it, coral reefs as we know them today wouldn’t exist,” he said.

“These species limit erosion in reefs that are often made up of mainly coral fragments, act as a nursery for many marine species, and are the main player in temperate reef formation along the Australian and New Zealand coastlines.”

The experiments took more than 18 months to complete. On average, the algae took six generations of about six to eight weeks each to develop resistance to ocean acidification.

The findings of the study are important in understanding how longer-lived species, such as tropical corals, could respond over multiple generations to ocean acidification.

“Coralline algae are a useful model species to test hypotheses about adaptation or acclimation over time as they grow to maturity in six weeks as opposed to several years for many coral species,” Dr Cornwall said.

The next step is to test a wider range of coralline algae species.

“This research focused on tropical coralline algae species from northern Australia, so the next step is to study temperate species—like those in southern Australian and New Zealand waters—that grow a lot slower and may not acclimatise to climate change as quickly.”

Cornwall C, Comeau S, DeCarlo T, Larcombe E, Moore B, Giltrow K, Puerzer F, D’Alexis Q, McCulloch M. (2020). Nature Climate Change. ‘A coralline alga gains tolerance to ocean acidification over multiple generations of exposure’. DOI: 10.1038/s41558-019-0681-8.

CONTACT

Dr Chris Cornwall (New Zealand)
P: +61 04 463 5720
E: Christopher.cornwall@vuw.ac.nz

Prof Malcolm McCulloch (Perth, WA)
E: Malcolm.McCulloch@uwa.edu.au