Australian Institute of Marine Science researcher Tim Cooper researching coral reefs off the coast of Western Australia yesterday. Picture: Eric Matson Source: Supplied

 

 

The findings undermine blanket predictions that global warming will devastate coral reefs, and add to a growing body of evidence showing corals are more resilient than previously thought, up to a certain point.

The study by the commonwealth-funded Australian Institute of Marine Science, peer-reviewed findings of which are published in the leading journal Science today, examined 27 samples from six locations from the West Australian coast off Geraldton to offshore from Darwin.

At each site, scientists took cores from massive porites corals – similar to a biopsy in humans – and counted back to record their age in much the same way tree rings are counted. Although some cores extended back to the 18th century, they focused on the period from 1900 to 2010.

The researchers found that, contrary to their expectations, warmer waters had not negatively affected coral growth. Quite the opposite, in fact: for their southern samples, where ocean temperatures are the coolest but have warmed the most, coral growth increased most significantly over the past 110 years. For their northern samples, where waters are the warmest and have changed the least, coral growth still increased, but not by as much.

“Those reefs have actually been able to take advantage of the warmer conditions,” said Janice Lough, a senior AIMS research scientist and one of the study’s authors.

Maria Byrne, a professor of marine biology at Sydney University, said after reading the paper that its findings “made perfect sense”. “Temperature rules metabolism, so it’s a no-brainer that if you get more temperature you will get more metabolism.”

She compared the findings to studies of sea urchins, where higher temperatures had been shown to offset the negative effects of ocean acidification, and to commercial aquaculture farms, in which some organisms are deliberately raised in warmer water to increase their growth rate.

The key question is how warm the water can get before the positive effects are reversed.

Lab studies have typically measured the effect of short-term, rapid changes in temperature and water chemistry; these mimic, for example, coral-bleaching events that are known to be devastating. Much harder to measure are the long-term effects of gradual warming, such as is caused by climate change.

A recent paper published in the journal Nature Climate Change, reported in The Australian, showed Zooxanthellae – the symbiotic organisms that live inside corals – can adapt much better to warming water than was previously thought. It is also known corals can, to a degree, change their Zooxanthellae with changing conditions.

Professor Byrne said the eggs of marine organisms laid in warmer water would pass that temperature tolerance on to the embryo, allowing ecosystems to evolve.

One of her recent papers, published in the Journal of Geophysical Research, showed sea cucumbers helped corals survive ocean acidification better.

Warming temperatures make coral bleaching more likely.