A potential breakthrough in saving Earth’s damaged coral reefs has been made by US scientists, who have shown that sound can be used as a tool to attract coral larvae to areas of coral that need regeneration.
But not just any sound will do. Just as humans associate certain sounds like birdsong or lapping water with well-being and a healthy environment, so coral larvae appear to respond positively to the sounds of healthy coral reef habitats, preferring to settle and grow where they can hear the bubbling and scuttling noises of fish and crustaceans.
The experiments
Researchers from the Woods Hole Oceanographic Institution in Massachusetts, working out in the Caribbean, off the Virgin Islands, based their work on findings going back to 2010, that initially showed that “coral larvae can detect and respond to sound”. That was the first time an auditory response had been noted in the invertebrate phylum Cnidaria, which includes jellyfish, anemones, and hydroids as well as corals. The corals were found to actively swim towards the sounds of reefs.
The latest research took things a step further, to test whether the corals had a preference for a certain sounding reef. The team played three different recordings in underwater speakers set up at three reefs. Two of the recordings played no additional sound, but one, set up at Salt Pond reef, played healthy coral reef noises, including the clicks, grunts, snaps, and scratches of the creatures that would normally inhabit a thriving reef.
The Salt Pond reef is an area where the coral reef has degraded, but the scientists found that the number of larvae swimming towards the healthy reef sounds and settling was 1.7 times that at the control sites.

Rainforests of the sea
The implications are huge. Coral reefs are sometimes called “the rainforests of the sea”, occupying under 0.1% of the oceans but providing a habitat for at least 25% of the world’s marine species. They also have a tourism value estimated at around $2.7 trillion. Besides being an important sea defence for many islands, absorbing wave energy by as much as 97%, they are also important carbon sinks, sequestering more CO2 than they release.
The precious ecosystems are under threat however, from a range of problems such as warming ocean conditions and pollution from human activity. If coral larvae can be attracted to reefs that have been bleached and depleted, there is potential to restore some habitats to their former glory.
Nonetheless, lead researcher, Nadège Aoki, cautioned that the work, published in the Royal Society Open Science journal, required further investigation and should not be used in isolation as a fix-all for coral regrowth. “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.”