As originally reported by The Guardian, the strange sounds of a coral reef, including an array of snaps, grunts, purrs, and foghorns, may help researchers gauge its health. This cacophony of fascinating fish songs has only attracted attention recently, and many of the noises are still unidentified - though scientists are using underwater speakers to try and keep the conversation going.
Recent research took place on a reef restoration site that had been devastated by dynamite fishing, a destructive practice using explosives to stun or kill all the fish in an area. While the coral that was destroyed was clearly rebounding, scientists wanted to know if the other inhabitants were returning.
Visual reef surveys are unreliable, often missing cryptic and camouflaged animals and species that are strictly nocturnal. So, they turned to the reef’s natural noises for clues - and what they discovered was surprising. The vibrant soundscape was very similar to those of reefs that were never damaged.
Sound is essential for survival on the reef because most of its inhabitants, from corals to crustaceans and fish, produce young that spend the first part of their lives in the open ocean. These juveniles then follow sound, along with other cues, to find their way back to the reef.
While numerous projects have successfully regrown corals around the world, their total success was uncertain. The return of a diverse array of wildlife, in this case, proved their work to be more than “a coral gardening project”, according to Lamont.
“Furthermore, as we listened through these hours and hours of recordings, we kept discovering sounds we had never heard. Some were a bit familiar, but some were just like, ‘I have no idea what that is’. It was a real sense of adventure and discovery,” he said.
A foghorn sound was especially intriguing for researchers. After downloading the noise to an MP3 player, the team decided to broadcast it via underwater speakers. Despite playing the call extensively and even hearing a response from the reef, no fish swam out to meet them. The team suspects it may be a type of toadfish based on its similarity to Caribbean recordings.
Lamont’s study, published in the Journal of Applied Ecology, analysed roughly four hectares of recovering reefs at the Mars Coral Reef Restoration Project in central Indonesia’s Spermonde Archipelago. At the start of the project, small pieces of live coral were mounted to star-shaped metal frames and placed in the rubble field left behind by dynamite fishing.
Researchers then compared these areas several years into recovery against areas still degraded and areas that were never damaged. They found most of the fish calls recorded were at least 50% more frequent in healthy and restored habitats.
A computer-generated model measuring the complexity of the soundscape also indicated the restored reefs were similar in diversity to the undamaged ones - suggesting a healthy and functioning ecosystem.
While the individual animals making these noises have not yet been identified, some specific sounds have previously been ascribed. Whooping noises have been linked to the Ambon damselfish, grunts and growls with soldierfish, and knocking or tapping with triggerfish. These diverse sounds can come from fishes’ drum-like swim bladder, their throats, and from teeth or bony plates being banged together.
This diversity of sound lends hope for the future, with scientists stunned at the fast and well-rounded recovery their test reef was making. Of course, a full rebound will take far longer, allowing extra time for rarer slow-growing corals to return.
Thankfully, the dynamite fishing around this test reef has been replaced by sustainable practices. But, scientists warn that restoration is not a complete solution. We still have to worry about all the threats to the world’s reefs, such as the climate crisis and water pollution. “If we don’t address these wider problems, conditions for reefs will get more and more hostile, and eventually restoration will become impossible,” Lamont said.