Helping Nemo Find Home: How Underwater “Coral” Concerts Restore Fish Populations to Dying Reefs!

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Some exciting research was published in late 2019 by a team of researchers from the UK and Australia looking at how to repopulate damaged coral reefs.¹ You might have seen headlines like “To Help Coral Reefs Come Back, Fake It (With Sound) ‘Til Fish Make It”² or “Scientists Used Loudspeakers to Make Dead Coral Reefs Sound Healthy. Fish Flocked to Them.”³

The bottom line is that the scientists placed underwater loudspeakers in dead patches of Australia’s devastated Great Barrier Reef and played recordings of previously healthy reefs. Compared to areas with no sound recordings, they found that twice as many fish arrived at those parts of the reefs and, remarkably, they stayed. ¹

Graph of juvenile fish abundance among Piscivores (fish that eat other fish) after 40 days. Image of fish was taken from the Lizard Island Field Guide (lifg.australianmuseum.net.au), licensed under the Creative Commons Attribution 3.0 License (creativecommons.org/licenses/by/3.0/).1

The team published their work in Nature Communications as an Open Access article licensed under a Creative Commons license which permits widespread sharing to get the information into the hands of a wide audience. Here is a map of the loudspeaker placement around degraded coral reef habitat.

From Gordon TAC et al. Acoustic enrichment can enhance fish community development on degraded coral reef habitat. Nature Communications 10, 5414 (2019). Figure 5. Satellite image obtained from Google Maps, available at https://goo.gl/maps/5Loa45HKYgJ2 (Map data: Google, GBRMPA). 1

Tim Gordon, a dynamic young marine biologist who was part of this innovative project, feels strongly that scientists must move beyond “doom-and-gloom narratives” about climate change because they only fuel “feelings of hopelessness that leads to apathy and inaction.” [ocean summit] In that spirit, we are sharing Tim’s own words here where he shares the thinking behind the “acoustic enrichment” study: ⁴

“Imagine yourself as a one-week-old coral reef fish. You hatched from an egg on the reef and immediately you are swept out into the open ocean to avoid predators for the first few days of your life. Now you’ve grown up a bit you’re big and strong and at the size of a Tic Tac. You’re ready to take on the world. You’re going to come back to your home reef and start adult life. But how on earth are you going to find your way home?

“This isn’t “Finding Nemo” so there aren’t going to be a bunch of friendly sea turtles pointing you in the right direction. This is the real world and you’re a very small fish lost in a very big ocean. You can see a coral reef, but only from about 20 meters away. You can smell a coral reef, but only if the currents going in the right direction. But crucially you can hear a coral reef.

“Our ears don’t work very well underwater. But when you listen with an underwater microphone through the ears of a fish, it’s a different world down there. Clownfish whooping, Cod grunt, and Parrotfish crunch their way through coral as they graze, and sea urchins scrape, and shrimp snap their claws. Together that makes a symphony of reef noise that can be heard from miles away.

“Nemo is literally hearing his way home…or at least he used to be. Climate change and warming seas have caused more damage to coral reefs worldwide in the last four years than they have in the whole of recorded history before that.

Tim Gordon explains how he’s ‘Helping Nemo Find Home’ – University of Exeter, 3 Minute Thesis

“At the start of my Ph.D. I listened to reefs. I compared how they sounded five years ago before that damage to how they sound today and it was the saddest thing I’ve ever heard. A great animal orchestra of the reef has been replaced by the sounds of silence and waves washing the shore.

“To test the implications of that for Nemo hearing his way home I set up an experiment where I made a lot of fake coral reefs all around a bay and I played either the sound of healthy reefs from five years ago or the sound of today’s degraded reefs. I counted the number of fish that heard the way home on to my reefs.

“What I found were there were far fewer fish arriving back when I played the sound of today’s reefs. That’s very worrying because those are the fish of the future. Those are the next generation of fish that are going to graze away algae and allow corals to grow and sustain the whole ecosystem for the hundreds of thousands of people that rely on it worldwide. Those fish need to make it home.

“That’s why I’m now interested in the future soundtrack of the Great Barrier Reef. How can we use acoustics—not just as a sad symptom of the decline of coral reefs—but as a tool to promote their recovery. If reefs aren’t loud enough, can we amplify them using loudspeakers? If we know which the key, the loudest organisms on reefs are, can we promote their conservation? And if reefs can’t be heard, can we reduce other sources of noise pollution in the ocean to make them audible from further distances?

In summary that today is my three-minute thesis. As well as looking for solutions to coral reef degradation, let’s try listening.” ⁴

The message here is one of hope; BBC’s Blue Planet II reveals that though our planet is damaged and changing rapidly, there’s still an enormous amount of diversity that remains and many species are quickly adapting to warming seas:

Here is another moving video that features Tim Gordon speaking at the 2018 World Ocean Summit about his lessons learned traveling areas of the ocean hardest hit by climate change over the last few years. He proposes three tangible and plausible actions that can be done today to turn things around before it is too late. You can hear it here and embedded below. ⁵

References

¹Gordon TAC et al. Acoustic enrichment can enhance fish community development on degraded coral reef habitat. Nature Communications, 2019; 10 (1) DOI: 10.1038/s41467-019-13186-2

²Garcia-Navarro L. To Help Coral Reefs Come Back, Fake It (With Sound) ‘Til Fish Make It. NPR. 1 December 2019. https://www.npr.org/2019/12/01/783932607/to-help-coral-reefs-come-back-fake-it-with-sound-till-fish-make-it

³Hawkins D. Scientists Used Loudspeakers to Make Dead Coral Reefs Sound Healthy. Fish Flocked to Them. Washington Post. 1 December 2019. https://www.washingtonpost.com/climate-environment/2019/12/01/scientists-used-loudspeakers-make-dead-coral-reefs-sound-healthy-fish-flocked-them/

⁴Tim Gordon “Helping Nemo Find Home” – 3 Minute Thesis 2017 Winner. University of Exeter. https://www.youtube.com/watch?v=eixMvMdF_cg

⁵Gordon, Timothy. “Climate Change: Tales From the Front Line.” Presentation at 2018 World Ocean Summit. WithTheEconomist. https://www.youtube.com/watch?v=q72ZZW9sSuA&t=3s