A phenomenon that makes coral spawn more than once a year is improving theresilience of the Great Barrier Reef.

The discovery was made by University of Queensland and CSIRO researchersinvestigating whether corals that split their spawning over multiple monthsare more successful at spreading their offspring across different reefs.

Dr Karlo Hock, from UQ’s School of Biological Sciences, said coral massspawning events are one of the most spectacular events in the oceans.

“They’re incredibly beautiful,” Dr Hock said.

“On Australia’s Great Barrier Reef, all coral colonies typically spawn onlyonce per year, over several nights after the full moon, as the water warms upin late spring.”

Study co-author Dr Christopher Doropoulos from the CSIRO Oceans & Atmospheresaid sometimes however, coral split their spawning over two successive months.

“This helps them synchronise their reproduction to the best environmentalconditions and moon phases,” he said.

“While reproductive success during split spawning may be lower than usualbecause it can lead to reduced fertilisation, we found that the release ofeggs in two separate smaller events gives the corals a second and improvedchance of finding a new home reef.”

The research team brought together multi-disciplinary skills in modelling,coral biology, ecology, and oceanography, simulating the dispersal of corallarvae during these split spawning events, among the more than 3800 reefs thatmake up the Great Barrier Reef.

They looked at whether the split spawning events more reliably supply larvaeto the reefs, as well as whether the ability to exchange larvae among thereefs is enhanced by them.

UQ’s Professor Peter J. Mumby said split spawning events can increase thereliability of larval supply as the reefs tend to be better connected and havemore numerous, as well as more frequent, larval exchanges.

“This means that split spawning can increase the recovery potential for reefsin the region.

“A more reliable supply of coral larvae could particularly benefit reefs thathave recently suffered disturbances, when coral populations need new coralrecruits the most.

“This will become more important as coral reefs face increasinglyunpredictable environmental conditions and disturbances.”

Dr Hock said the research also revealed that the natural processes of recoverycan sometimes be more resilient than originally thought.

“However, even with such mechanisms in place, coral populations can onlywithstand so much pressure,” he said.

“It all ends up being the matter of scale: any potential benefits from splitspawning might be irrelevant if we don’t have enough coral on these reefs toreproduce successfully.

“Mitigating well-established local and global threats to coral reefs – likeriver runoffs and carbon dioxide emissions – is essential for their continuedsurvival.”

The study between UQ, CSIRO and ARC Centre of Excellence for Coral ReefStudies was published in Nature Communications (DOI:10.1038/s41467-019-11367-7).

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