The Achilles heel of coral growth is high temperatures, not ocean acidification

The Achilles heel of coral growth is high temperatures, not ocean acidification, according to researchers from the ARC Centre of Excellence for Coral Reef Studies and The University of Western Australia. The research will be presented tomorrow in Canberra.

The researchers say that corals will find it increasingly difficult to build strong skeletons as the world’s oceans rapidly warm. Global-scale coral bleaching events are becoming more frequent and intense, potentially compromising the future of coral reefs.

In recent studies, Professor Malcolm McCulloch from the ARC Centre of Excellence for Coral Reef Studies (Coral CoE) and The University of Western Australia (UWA) found that under ocean acidification, corals can still build skeletons, or “calcify.” However, they lose this ability when they bleach under the extreme heat events that now characterise global warming.

Professor McCulloch said coral calcification, a process vital for building reefs, was dependent on a partnership between coral and their photosynthetic algae (zooxanthellae).

“Corals fine-tune their internal pH to maximise the supply of carbon and energy from their zooxanthellae. This can then lead to calcification, or skeleton-building,” Professor McCulloch said. “However when there are abrupt increases in seawater temperatures this relationship breaks down; the corals become stressed and expel their zooxanthellae. This leaves them with little energy to survive. Unless the temperature drops and the zooxanthellae are able to recolonise in the coral, the coral may die.”

Stony corals build the iconic tropical coral reef networks that dominate many shallow-water environments, harbouring more than one-third of the oceans’ biodiversity. Professor McCulloch examined massive Porite corals collected from the Great Barrier Reef (GBR) and from Coral Bay Ningaloo Reef. A coral core collected from the GBR was used to look directly at the impacts of the global bleaching event of 1998 — which is still the warmest summer on record for the central section of the GBR.

One of Professor McCulloch’s studies concludes that, “the increasing frequency and intensity of coral bleaching events due to CO₂-driven global warming constitutes the greatest immediate threat to the growth of shallow-water reef-building corals, rather than the closely associated process of ocean acidification.”

Professor McCulloch will present “The Achilles Heel of coral calcification” tomorrow at 11am in the Global Change session of the Coral Reef Futures Symposium at the Shine Dome in Canberra.

“Response of coral calcification and calcifying fluid composition to thermally induced bleaching” is published in Scientific Reports at: https://www.nature.com/articles/s41598-017-02306-x

“Coral calcification in a changing World and the interactive dynamics of pH and DIC upregulation” is published in Nature Communications at: https://www.nature.com/articles/ncomms15686

All media are invited to attend the Coral Reef Futures Symposium, 15–16 June 2017 at the Shine Dome, Canberra: https://www.coralcoe.org.au/crs_event/coral-reef-futures-symposium-2017

CONTACTS FOR INTERVIEWS

Prof Malcolm McCulloch
ARC Centre of Excellence for Coral Reef Studies & UWA
Phone: 0457 939 937
Email: malcolm.mcculloch@uwa.edu.au

Catherine Naum
Communications Manager, ARC Centre of Excellence for Coral Reef Studies
Phone: 0428 785 895
Email: catherine.naum1@jcu.edu.au