Coral bleaching badly affected reefs of Kimberley, study finds

Extract from The Guardian

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Coral

Up to 80% of Kimberley’s inshore reef bleached in El Niño heatwave of 2016, with about 29% of the coral at Rottnest, off Perth, also affected

Up to 80% of corals in inshore reefs in the Kimberley were bleached in the 2016 El Niño heatwave. Photograph: Morane Le Nohaic/University of Western Australia

Calla Wahlquist

Saturday 4 November 2017 17.05 AEDT Last modified on Saturday 4 November 2017 17.13 AEDT

Up to 80% of coral in inshore reefs in the Kimberley was bleached during the global mass bleaching event that also affected 93% of the Great Barrier Reef in the summer of 2016-2016, according to new research.
Led by scientists from the University of Western Australia and published in Scientific Reports this week, the research found between 57% and 80% of corals in the Kimberley, particularly at Montgomery Reef, the largest inshore coral reef in Australia, were bleached in April 2016.

About 29% of the coral at Rottnest, off the coast of Perth, was also bleached during the 2015-2016 summer. The world heritage listed Ningaloo reef and a reef further south, at Bremer Bay, were not affected.
It is the first time the Kimberley’s famously tough inshore coral reefs have been affected by a mass bleaching event and the first time a reef along the Western Australian coastline has been severely affected by a bleaching event triggered by an El Niño heatwave.
“This is the first documented regional-scale bleaching event in WA during an El Niño year and the first time we have been able to measure the percentage of impacted corals in 2016,” University of Western Australia research associate Verena Schoepf said.

An aerial view of an inshore reef in the Kimberley which has been affected by coral bleaching. Photograph: Steeve Comeau/University of Western Australia

Coral reefs in the Kimberley are considered resistant to temperature change because 12-metre tides and water surface temperatures of about 30C for five months over summer can cause daily temperature fluctuations of up to 7C.
In early 2016, researchers found, ocean surface temperatures in the Kimberley increased by between 4.5C to 9.3C.
They conducted detailed underwater surveys of five sites across four different regions from tropical to temperate waters along the WA coast. The surveys were conducted both before and after the bleaching event, which was forecast by the United States National Oceanic and Atmospheric Administration in late 2015.
The 2015-2016 El Niño heatwave caused the largest recorded global mass bleaching event since the 1980s, affecting 38% of coral reefs worldwide. It followed mass bleaching events in 1998 and 2010, also associated with El Niño-southern oscillation driven warming events.

It is the first time corals on the WA coast have been affected by a global bleaching event since the summer of 2010-2011, when a strong La Niña event bleached between 72% and 92% of the corals at Ningaloo and between 12% and 100% of the corals at the Houtman Abrolhos islands.
“Coral reefs in WA are now at risk of bleaching during both El Niño years, such as in 2016, and La Niña years, such as 2010-2011,” Schoepf said. “But the geographic footprint differs – the northwest is at risk during El Niño years, whereas Ningaloo Reef and reefs further south are at risk during the La Niña cycle.”
Coral bleaching occurs when high sea temperatures cause corals to expel zooxanthellae, the photosynthetic algae which gives coral its colour. If the temperature returns to normal and the algae returns to recolonise the reef, the coral can survive.
If the algae does not return, the coral dies. In the Great Barrier Reef, which was hit with a double bleaching event in 2016 and then 2017, an estimated 29% of shallow-water coral has died. In areas north of Port Douglas, it is closer to 70%.