If a porkfish swims by and no one is there to hear it, does it make a sound?
A new effort to monitor the seas by sound says, resoundingly, yes. The ocean—especially busy places such as coral reefs—can be noisy. Mantis shrimp snapping, damselfish whooping. (Listen to the music of a cacophonous reef here.) Other places have whales singing and oysters crackling. Not to mention all of that human-made noise.
But so much of the ocean chatter has been difficult to parse out. Who made this whoosh or that pop? Answering these questions could provide detailed profiles of the inhabitants of particular ecosystems, and, by proxy, their ecological health.
In recent years, scientists have mostly relied on visual surveys and environmental DNA to get a glimpse of ocean ecosystems. But these methods have drawbacks. A visual survey can only capture a single point in time. And environmental DNA—the genetic traces organisms leave behind—generally can’t tell researchers much about where or when the creatures it belonged to were swimming by. Sound, however, especially when paired with video tracking, could overcome these shortcomings.
Who made this whoosh or that pop?
A team of scientists at the FishEye Collaborative is deploying both in tandem to make sense of the chatter of a coral reef in Curaçao in the Caribbean. With a video camera that tracks fish using essentially 360-degree vision, and microphones to match, their system purports to be able to parse the sounds of the reef and to assign specific noises to different species of fish. They say they’ve collected the largest library of species-specific fish sounds yet. Their work was published this month in Methods in Ecology and Evolution.
Paired with machine learning, the researchers suggest their system could work like smartphone apps that can identify birds by their calls. Similar efforts to use bioacoustics for conservation efforts are rolling out in all sorts of biomes to track all sorts of animal populations, including leopards in Tanzania.
This acoustic monitoring could be a helpful tool in the effort to preserve and restore coral reefs, which are key to the health of the ocean. Not only do they help buffer land from increasingly strong storms, but they also provide a vast amount of food for the planet. And they are, of course, seriously suffering. “Governments and NGOs are investing billions in reef protection and restoration,” Marc Dantzker, executive director of FishEye Collaborative and co-author of the study, said in a statement. “We need to ensure that we spend these limited funds effectively. We need to track how reefs are responding both to the stressors and the interventions.” And he suggests that this sort of long-term sonorous monitoring will be a boon to that effort.
Tracking ocean acoustics in this methodical way could also surface new and obscure sounds, says Matt Duggan, a fellow study co-author who also works in the Center for Conservation Bioacoustics at the Cornell Lab of Ornithology. “Until now, the ‘loudest’ species, like dolphins, whales, and snapping shrimp, have overshadowed the many other voices in the sea,” says Duggan. Uncovering the hidden voices can help scientists better measure the health and resilience of reefs the world over. The animals’ sounds have been there all along, of course. We just hadn’t been listening. 
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Lead image: Peter Leahy / Shutterstock