Marine heatwaves are having a marked impact on coral reef systems off the Pilbara coast. A CSIRO and University of Western Australia study in progress found bleaching and decimation of ancient porite corals - many up to 400 years old - in a recent visit to Barrow Island. The oceans around Australia were unusually warm in 2013. Globally the deep oceans are also continuing to warm.
“We suspect this bleaching event was due to marine heatwaves that occurred in the region over the past few summers, and to see it up close was sobering,” said Dr Russ Babcock, CSIRO lead scientist, “But to offset this loss, some reefs only a short distance north showed much less damage and will continue to contribute to a healthy ecosystem."
A marine heatwave extreme bleaching event ocurred in 2011 that was widely spread along the Western Australian coast. Preliminary results from the study show that further damage was done in the 2012-2013 summer with elevated water temperatures.
"There had been coral bleaching in the region that occurred in, not just 2011 when there was an extreme heatwave, but also earlier this year and we found that virtually all of the staghorn and tail corals had been killed and even some of the extremely old giant mass of porites corals had died. So these recent conditions have probably been some of the most extreme experienced there for several hundred years." said Dr Babcock.
Porite corals were thought to be resiliant to variations in the marine climate and are regularly buffeted by tropical cyclones that hit the Pilbara.
"This region in the West Pilbara is right in the middle of an area of very high biodiversity value." said Dr Babcock.
The West Pilbara region is also a focus of major industrial development from oil and gas, and exporting of iron ore. The study is funded by the Gorgon Project’s Net Conservation Benefit Fund, which is administered by the Western Australia Department of Parks and Wildlife. The Gorgon Project is a joint venture of the Australian subsidiaries of Chevron (47.3 per cent), ExxonMobil (25 per cent), Shell (25 per cent), Osaka Gas (1.25 per cent), Tokyo Gas (1 per cent) and Chubu Electric Power (0.417 per cent).
“To see them badly damaged, or completely dead, as a result of bleachings that happened over previous years, and likely the one in 2013, was surprising,” lead scientist Dr Babcock said in a Guardian report.
University of Western Australia professor Malcolm McCullough comented, “It’s almost unprecedented. These corals were living for hundreds of years. And they died in the summer of 2012-13.
Corals already need to battle ocean acidification, nutrient pollution, as well as warming waters. High sea surface temperatures damage the algae that lives in symbiosis with the coral polyp, which is then ejected from the coral, turning it white.
“Bleaching is not unusual, it’s been occurring now for about 20 years,” McCullough said. “But by looking at the longer records the bleachings appear to be more common.”
Sea surface temperatures continue to be unusually warm around Australia in 2013.
The future does not bode well for coral reef ecosystems. Controlled experiment show coral reefs are in peril in a high CO2 world. Scientific modelling shows that atmospheric warming of 2 degrees celsius is too much for nearly all the world's coral reef ecosystems.
Sources:
- CSIRO, 13 February 2014 - Pilbara marine health check - good and bad news
- Michael Safi, The Guardian, 13 February 2014 - Coral off WA suffers shocking damage from marine heatwaves, scientists say
- Image: CSIRO - Dr Tim Langlois, UWA, with a 400 year old Porites coral head that has succumbed to coral bleaching, off Montobello Island.
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