Researchers have used the sounds of healthy reefs to entice fish back to areas where coral has been wiped out on the Great Barrier Reef.

Key points: Fish numbers doubled and species increased by 50 per cent on acoustically "enriched" sites

Fish numbers doubled and species increased by 50 per cent on acoustically "enriched" sites Coral polyps have also been found to navigate toward healthy sounding reef, despite not having ears

Coral polyps have also been found to navigate toward healthy sounding reef, despite not having ears Bigger stressors like climate change, pollution and overfishing still need to be addressed

They took recordings of shrimp snapping, fish grunting and other sounds taken from healthy regions of reef and played them on underwater speakers at a bunch of "coral-rubble patch reefs" at Lizard Island.

The number of fish doubled at the sites where they placed the speakers compared with control sites with no audio over the 40-day study period, they reported in Nature Communications.

They also found the number of different types of fish — the species richness — increased by 50 per cent during that time.

The researchers hope their findings may help in restoring some of the ecosystem functions to coral reefs that have suffered bleaching or been hit by cyclones or other impacts, said Tim Gordon, lead author and PhD student from the University of Exeter.

"Fish are crucial for coral reefs to function as healthy ecosystems," Mr Gordon said.

"Boosting fish populations in this way could help to kick-start natural recovery processes, counteracting the damage we're seeing on many coral reefs around the world."

Juvenile fish are known to use reef acoustics to find their way to healthy reefs after they're spawned in open water.

Damaged reefs are much quieter than healthy systems, according to research published last year in the journal PNAS by an international team that included Mark Meekan from the Australian Institute of Marine Science (AIMS).

At the time Dr Meekan, who also worked on this research, described the sound of a healthy reef as like "listening to bacon in a frying pan".

"It's punctuated by the chirps and tweets and all sorts of screeches that come from fish," he said.

"Baby fish that have been drifting off into the open water have to find their way back home, and what they use is sound."

Attracting fish to a dead reef 'won't bring it back' immediately

The technique may help with reef restoration, but it is only likely to have localised benefits. ( Supplied: Harry Harding/University of Bristol )

While it's one thing to get the fish to the reef, there's still the problem of what they can eat, and where they can hide on a degraded patch.

While the amount of juvenile fish was increased over the whole 40-day study period, it would be telling to monitor the reefs after a year or more to see if the benefit is long-lasting, according to Ivan Nagelkerken from the University of Adelaide.

"Corals form a habitat for local animals, so just restoring the fish might not be very effective," said Professor Nagelkerken, who wasn't involved with this study.

"It's definitely interesting to see that the mechanism works, but is it a solution?"

However, he said that his previous research published in the journal PLOS ONE found that despite not having ears, coral larvae also seemed to use sound to find and settle on reefs.

"They don't have ears but somehow they're attracted to healthy reef sounds," he said.

"Maybe they can sense the vibrations with their cilia [tiny hair-like appendages], but we don't know.

"[But] there's the opportunity that if you play healthy reef sounds you may bring back a much richer reef community than just fish."

The researchers acknowledged this was not a silver bullet for reef recovery.

Firstly, it would be impossible to fit any ecologically significant number of reef patches with speakers.

But it may give a boost to reef sites that are identified for active recovery efforts, Dr Meekan said.

"Attracting fish to a dead reef won't bring it back to life immediately," he said.

"But recovery is underpinned by fish that can clean the reef and create space for corals to regrow."

To move reef recovery beyond localised applications such as this one, the bigger issues must be fixed, Professor Nagelkerken said.

"It doesn't solve the greater issue of how we are [harming] the oceans via pollution, climate change and ocean acidification, habitat destruction and overfishing," he said.

"If we don't remove those stressors then reef restoration is not going to happen."