Scientists eavesdropping on a previously destroyed coral reef in Indonesia say the ecosystem is abuzz with new life, including the "whooping, croaking and growling" of reef fish. The reef has been re-seeded with new corals as part of a decade-long restoration effort, and researchers were curious if marine animals were returning to the area. By listening in on the reef using underwater microphones, the team recorded a cacophony of bizarre fish songs on the previously quiet reef—some of which have never been documented before—suggesting a remarkable recovery, according to a new study published in the Journal of Applied Ecology.
“We listened through these hours and hours of recordings, we kept discovering sounds we had never heard,” says study lead author Tim Lamont of the University of Exeter to the Guardian’s Damian Carrington. “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.”
Before the restoration efforts started, the reef had been devastated by blast fishing, a destructive fishing method that uses explosives to kill or stun fish, and destroys corals in the process. Corals are often mistaken for plants because they take root on the seafloor, but a single coral is made up of thousands of tiny animals called polyps. When corals get damaged from disease, warm waters or blast fishing, they lose their vibrant colors, leaving behind a white skeleton in a process called coral bleaching. Once a reef dies, so does its ability to support diverse ocean life like fish, lobsters, seahorses, sponges, and sea turtles.
To revive the damaged ecosystem, scientists at the Mars Coral Reef Restoration Project have been re-seeding the area with new corals on hexagonal metal frames called "reef stars." Years into the restoration efforts, they wanted to know if the creatures that inhabit reefs were also returning.
Visual inspections are the most common way of checking up on a reef’s health, but audio recordings can catch things our eyes miss, like camouflaged or nocturnal animals. By using underwater microphones called hydrophones to analyze roughly four hectares of recovering reefs in the Spermonde archipelago in central Indonesia, the researchers were able to get a more complete view of the ecosystem’s recovery.
The team says their audio recordings tell a hopeful story: the once-dying reef has transformed into a robust and diverse soundscape. Their recordings revealed that healthy reef habitats had similar levels of coral cover and marine diversity as the restored reef, reports Inverse’s Tara Yarlagadda. By listening in on the reef, they captured sounds and fish songs like purrs, croaks, growls, raspberries, foghorns, and even a first-ever fish “laugh.”
“The foghorn one really blew our minds,” Lamont says to the Guardian. “I got really enthusiastic about trying to work out exactly what fish was making it. So I downloaded the noise onto an MP3 player and... I was swimming around blasting it out, trying to get a call and response going. I thought I got it replying a few times, but I never saw the fish itself swim out to meet the call. So the mystery continues.”
Lamont notes that such restoration efforts are only possible if we address threats like climate change 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,” he says in a statement.