One Way to Lure Fish Back to Damaged Reefs? Play the Sounds of Living Coral

Coral reefs are perhaps most recognizable by their stunning visual displays—from the purplish plumes of sea sponges to the rainbow-tinted scales of wrasses.

But a reef’s colorful array isn’t the only thing that’s striking: The healthiest reefs are also some of the noisiest. Crustaceans snap their claws; fish signal to each other through whoops, hums and grunts. The cacophony comes together to create “a dazzling biological soundscape,” Stephen D. Simpson, a marine biologist at the University of Exeter, explained in a press release.

These appealing symphonies can do more than please the ear. As Simpson and his colleagues reported last week in the journal Nature Communications, playing the sounds of healthy corals through loudspeakers could lure community-building fish back to degraded reefs—and potentially speed their recovery.

The team’s technique, called “acoustic enrichment,” joins a growing list of unorthodox restoration methods to combat the effects of climate change, pollution and overfishing on coral reefs, reports Derek Hawkins at The Washington Post. In some regions, scientists have planted corals in nurseries, where they dangle from metal “trees.” Other researchers have taken evolution into the lab, cultivating heat-resistant corals that might have a better shot of weathering rising temperatures.

But the new study is the first to take this auditory approach. Young fish, including many essential to reef rehabilitation, “home in on [the sounds of healthy reefs] when they’re looking for a place to settle,” Simpson said in the press release. This drives a positive cycle of enrichment, as noisy fish settle near corals and attract even more biodiversity. As reefs deteriorate, however, they spiral into silence, deterring fish from dropping by.

To see if they could flip the balance in damaged ecosystems, Simpson and his team placed patches of dead coral in 33 locations around Australia’s Great Barrier reef. Two-thirds of the faux reefs also got underwater loudspeakers, some of which turned on each night to blast the sounds of healthy reefs, while others remained silent.

After six weeks of these midnight serenades, the noisy sites were home to twice as many fish than the silent ones. They also contained 50 percent more species, supporting creatures from all parts of the food web. And the bustling hubs seemed to have serious staying power: Attracted by the lullabies of life, fish arrived faster and stuck around longer.

Implemented on a larger scale, the technique has the potential to “kick-start natural recovery processes,” explains lead author Tim Gordon, a marine biologist at the University of Exeter, in the press release.

But Gordon also cautioned that the new technique merely provides relief, not a cure. “This is potentially a useful tool for attracting fish towards areas of degraded habitat,” he told Nicola Davis at The Guardian, “but...it is not a way of bringing back a whole reef to life on its own.”

Restoring reefs to their former glory will require tackling the biggest root of the issue: climate change, Catherine Head of the Zoological Society of London and the University of Oxford, who was not involved in the study, told Davis. Due in large part to heat stress, coral reef bleachings are occurring four times as frequently as they did in the 1980s—and scientists have warned that the world’s oceans may now be changing too quickly for some reefs to recover.

“Our biggest tool in the fight for coral reefs is the 2016 Paris climate change agreement to curb global CO2 emissions,” Head told Davis. But acoustic enrichment, she said, is “a novel tool which can add to the reef conservation toolbox.”

In combination with other conservation efforts, tunes like these could someday help coral reefs crackle back to life—long before they sing their swan songs instead.

Katherine J. Wu | | READ MORE

Katherine J. Wu is a Boston-based science journalist and Story Collider senior producer whose work has appeared in National Geographic, Undark magazine, Popular Science and more. She holds a Ph.D. in Microbiology and Immunobiology from Harvard University, and was Smithsonian magazine's 2018 AAAS Mass Media Fellow.