Promiscuous corals may survive bleaching

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Some corals can acquire new types of algae from their environment after bleaching, which may make the coral more heat-tolerant and enhance their recovery.

Most corals were previously believed to only acquire microalgae in their juvenile stage, and to house the same algae types for their lifetime.

“Our study shows for the first time that some adult corals can be promiscuous, and swap their algal partners later in life, says Nadine Boulotte, a Southern Cross University postgraduate student, who led the research.

“This algae partner-swapping could help corals to better adapt to climate change and survive bleaching events if they can acquire more heat-tolerant microalgae.”

Coral bleaching occurs when the microalgae living within coral polyps die off, leaving the coral tissues white. These microalgae are essential for coral survival and live in a symbiotic (mutually beneficial) relationship, providing corals with much of the energy they need for reef building.

The team used new DNA sequencing techniques to analyse thousands of algal symbionts from corals in the beautiful subtropical reef at Lord Howe Island during and after the coral bleaching events of 2010 and 2011.

"We monitored the diversity and dominance patterns of the symbiotic microalgae present in polyp tissues of two coral species and found an extraordinary range of different types of microalgae present in the corals,” said Ms Boulotte.

"Even more exciting was that some of the corals surviving the bleaching events appeared to have acquired new algal types from the surrounding environment.

"One of these new types of microalgae became very abundant, occupying about one-third of the microalgal community present in the coral population sampled."

The research included scientists from SCU’s Marine Ecology Research Centre, the University of Melbourne, the Australian Institute of Marine Science (AIMS) and the University of Hawaii.

Professor Madeleine van Oppen from the University of Melbourne and Australian Institute of Marine Science (AIMS) was a co-author on the study.

"This is the first evidence that symbiont switching can occur in adult corals, as previously it was believed that uptake of new types of symbiotic microalgae was restricted to coral larvae or juvenile coral polyps," Professor van Oppen said.

"These results highlight a mechanism of corals to cope with increased sea temperatures that had previously been hypothesised to exist, but never been shown to actually occur."