Underwater speakers that broadcast the hum of thriving coral could bring life back to more damaged and decaying reefs that are in danger of becoming ocean graveyards, researchers say.
Scientists work from the US Virgin Islands in the Caribbean Islands found that coral larvae were up to seven times more likely to settle at a struggling reef where they played recordings of the squeals, moans, grunts and scratches that make up the symphony of a healthy ecosystem.
“We’re hoping this might be something we can combine with other efforts to put the good stuff back on the reef,” said Nadège Aoki at the Woods Hole Oceanographic Institution in Massachusetts. “You can leave a speaker for a certain amount of time and it can attract not only coral larvae but fish back to the reef.”
The world has lost half of its coral reefs since the 1950s by the devastating impact of global warming, overfishing, pollution, habitat loss and disease outbreaks. The steep declines have fueled efforts to protect remaining reefs through approaches ranging from replanting with nursery-raised corals to developing resilient strains that can withstand warm water.
Aoki and her colleagues took another shot, building on previous research that had shown this coral larvae swim to reef sounds. They set up underwater speakers at three reefs off St. John, the smallest of the US Virgin Islands, and measured how many coral larvae, kept in sealed containers of filtered seawater, settled on pieces of rocky ceramics in the containers. 30 meters from the speakers.
While the researchers installed loudspeakers at all three sites, they only played sounds from a thriving reef at one: the degraded Salt Dam Reef, which was bathed in the marine soundscape for three nights. The other two sites, the degraded Cocoloba and the healthier Tektite reefs, were included for comparison.
When coral larvae are released into the water column, they are carried on the currents and swim freely before finding a place to settle. Once they fall to the seabed, they become attached to the site and mature if they survive.
Write in the Royal Society Open Science magazine, the researchers describe how, on average, 1.7 times more coral larvae settled at the Salt Dam Reef than at the other sites where no reef sounds were played. The settlement rates at Salt Pond decreased with distance from the speaker, suggesting that the broadcasts were responsible.
Although the results are promising, Aoki said more work is underway to understand whether other coral species respond to reef noise in the same way, and whether the corals thrive after they settle. “You have to be very thoughtful about the application of this technology,” she said. “You don’t want to encourage them to settle where they will die. It really has to be a multi-pronged effort with steps in place to ensure the survival of these corals and their growth over time.”
Prof Steve Simpson, a marine biologist at the University of Bristol who was also involved in the study that found coral larvae respond to reef sounds, has been using audio recordings to attract fish larvae to reefs for 20 years. He said the work was “exciting” and demonstrated how acoustic playback can promote coral settlement in reef habitats.
“We are in a race against time to secure the future of coral reefs as we drive for net zero and begin to fix the climate,” Simpson said. “Coral reefs are the first marine ecosystems we can lose to climate change, which means they are also the first we can save. If we can save reefs, we can save anything.”
