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In 2016, Stephen Simpson, a marine biologist at the University of Bristol in England, returned to a study site off Australia’s Lizard Island, part of the Great Barrier Reef. Back-to-back cyclones that smashed reefs and turned corals upside down had hit in 2014 and 2015, followed by a massive bleaching event in 2016, which ravaged the coral ecosystem. After all that, “It was like swimming in a graveyard,” Simpson says.
Feeling “absolutely devastated,” Simpson and graduate student Timothy Gordon decided to channel their grief into action. In 2017, they heaped up coral rubble to build dozens of new miniature reefs. They placed speakers nearby to play recordings made when the reefs were healthy. Twice as many young fish settled on the reefs near these speakers. “We found that we could actually start to rebuild the reef community,” Simpson says.
Simpson and Gordon’s project is just one of a growing number of research efforts that show that sound may be a critical tool for ensuring the future of the ocean. In a new paper, Brittany Williams, a graduate student at the University of Adelaide in Australia, reviewed projects that used sound to help restore ecosystems, both in the ocean and on land, or that studied how sound attracts animals. “We wanted to try and get this word out there that sound has great potential,” she says.
That potential arises from the fact that a healthy ocean is noisy: fish whistle and grunt, sea urchins scrape food from the seabed, dolphins squeal, and spiny lobsters play their antennae like violins. Animals like all this noise. Like the bustle of a big city, the familiar din of a healthy habitat attracts young creatures that are seeking a permanent home.
In some of these earlier experiments, scientists broadcast bird calls to draw seabirds, including Arctic terns and marbled murrelets, to new nesting sites. In the ocean, researchers have found that sound is one of the cues baby fish use to find and settle on a coral reef after spending their first weeks swimming in the open ocean. “We realized that the fish might be hearing their way home,” says Simpson.
“The acoustic world underwater is critical for the survival of most animals,” Simpson says. “We are starting to see the world from their perspective in a way that we don’t, really, when we simply swim around with our eyes open.”
Williams’s own research demonstrates the power of sound. In experiments begun during her postgraduate degree in Australia, she looked at how sound can help oyster larvae choose where to settle. The tiny animals, barely big enough to spot without a microscope, have a little foot that “kind of flaps about” to help them reach their chosen location, Williams says. “Then they stick onto it and grow into the adult oyster, and they stay there forever.”
In the lab, Williams put oyster larvae into jars and played some of them a recording from a barren site where an oyster reef used to be. Other oysters were played nothing, while a third group heard the sound of a restored reef that crackled and popped with snapping shrimp. The larvae that heard the restored reef were about twice as likely as the others to settle and attach themselves at the bottom of the jar.
Seeing the difference, “I was like, wow, I almost can’t believe it!” Williams says. “I ran off and told my supervisors.” The results helped motivate Williams to pursue a PhD and continue this research, she says. “It’s exciting to have a bit of a role in figuring all of it out.”
Simpson is now doing experiments in the Caribbean to see how well sounds attract fish there. Williams has started her own field experiments, playing reef sounds to attract oyster larvae. She’s hoping to learn which elements of the soundscape oysters like best, and whether it’s possible to attract larval oysters without also drawing fish that will eat them.
Simpson says audio playback is an exciting tool that may soon enhance reef restoration projects in the wild. People are already rebuilding reefs and waiting for ocean life to populate them. Sound could speed up that process.