Coral bleaching detected off Kimberley coast

Scientists have discovered a significant coral bleaching event at one of Western Australia’s healthiest coral reefs.

More than 250 kilometres west of Broome, the Rowley Shoals is one of only two reef systems in the State to have recorded high and stable coral cover throughout the past decade.

In April and May 2020, the Australian Institute of Marine Science (AIMS) and the Department of Biodiversity, Conservation and Attractions (DBCA) conducted surveys of the reef system, supported by Parks Australia and Australian Border Force, to confirm reports of significant coral bleaching.

Data obtained revealed that bleaching was variable across the Rowley Shoals, with estimates ranging between one and 30 percent of the corals bleached. One site on Clerke Reef experienced up to 60 percent of the corals bleached.

Further aerial surveys of the North Kimberley and Lalang-garram marine parks found coral bleaching to be patchy and less severe than at Rowley Shoals.

Aerial view of several white coral colonies beneath the water's surface
Following temperature alerts issued by the Bureau of Meteorology (BOM), aerial flights by Australian Border Force provided the first evidence of coral bleaching at Western Australia’s remote coral reef atolls Image: Australian Border Force

DBCA’s Marine Monitoring Coordinator Dr Thomas Holmes attributed the bleaching to an unusually warm and prolonged ocean temperature off the coast of the Kimberley.

“By global standards, Western Australia still has relatively healthy reefs, but seawater temperature is increasing around the world as a result of climate change. This is causing corals to bleach and die from heat stress more frequently and at scales not previously observed,” Dr Holmes said.

Coral reef scene at Rowleys with bleached corals and fish
The extent and severity of bleaching varied across the Rowley Shoals, ranging from 10% to over 60% bleaching at some sites. Image: Chris Tucker

AIMS’ coral ecologist Dr James Gilmour said that bleaching had badly affected other offshore atolls and the inshore Kimberley region in 2016/17.

“Coral bleaching can devastate entire reef systems and dramatically alter associated communities of marine plants and animals,” Dr Gilmour said.

“Some corals will regain their symbiotic algae and recover, while those corals that have been severely bleached are likely to die.”

Large white boulder corals
At the worst affected sites, even the robust massive corals at 20m depth had bleached. Image: Chris Tucker

Follow up surveys as a part of DBCA and AIMS long-term monitoring programs are currently planned for later this year to determine the full effect of the event on the coral communities.

The bleaching survey of Rowley Shoals was conducted as part of AIMS’ North West Shoals to Shore Research Program funded by Santos Ltd.

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