Ocean warming drives coral growth rates in Western Australia

Both rising ocean temperatures and ocean acidification pose serious long-term threats to coral reefs, but findings recently published in the prestigious scientific journal, Science, have helped clarify the relative impact of these two threats to date. In their study on reefs off the coast of Western Australia, AIMS researchers found that rates of ocean warming are the primary drivers of recent changes in coral growth rates.

Using underwater drilling equipment, AIMS’ research team extracted cores from massive, long-lived corals from reefs across a 1000km north-south gradient in WA. These corals have characteristic annual growth bands, formed as the coral puts down skeleton. This process, known as calcification, forms the backbone of tropical coral reef ecosystems. Changes in growth rates were examined by measuring the annual growth bands; the most reliable method currently available for assessing changes in calcification rates of corals over long time periods.

Focussing in on the most recent 110 years, when measured coral calcification rates can be compared with observed sea temperatures, they found no evidence of a recent widespread decline in coral calcification rates on Australia’s western coral reefs. Corals at the most northerly sites, where sea temperatures are already high and warming has been small, have shown no change in calcification. In contrast, calcification rates of corals have increased at the most southerly reef sites, where sea temperatures are cooler and warming has been greater.

“This is an important finding, as it helps us better understand the effects of warming waters and rising CO2levels on coral reefs around Australia and globally,” says Dr Tim Cooper, former AIMS Research Scientist. “Rapid warming of parts of the tropical oceans, observed to date, appears to be driving coral calcification responses. Some corals in some locations are able to keep up with these changes, whilst others are already showing that the temperature changes have exceeded optimal conditions for coral growth.”

“We are now in an era of rapid environmental change for the world’s coral reefs and this study provides another line of evidence that coral reefs are sensitive to these changes. Coral calcification rates are clearly responding in the short term to temperatures, but in the longer term these responses will be compounded by the progressive impacts of ocean acidification” says Dr Janice Lough, Senior Principal Research Scientist at AIMS. “Limiting the magnitude of these rapid environmental changes is fundamental to providing coral reefs, as we know them, with a future.”

The new $35 million, National Sea Simulator, currently being built at AIMS in Townsville will give scientists the ability to regulate temperature, acidity, salinity, sedimentation and contaminants in large volumes of water. As a result, critical questions about the impact of our changing environment on coral reefs will be investigated in a controlled but realistic setting.

Contact details:

Dr Tim Cooper, AIMS Adjunct Research Scientist, (08) 6224 2787

Dr Janice Lough, AIMS Senior Principal Research Scientist, (07) 4753 4248

Wendy Ellery, AIMS media liaison, (07) 4753 4409; 0418 729 265; w.ellery@aims.gov.au

Australian Institute of Marine Science. Press release.

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