We might think of the world beneath the ocean’s surface as a quiet, peaceful one, but it would be far from true. Fish are noisy, the coral reefs where they congregate particularly so. With this in mind, an international team of scientists working on the Great Barrier Reef (including members from the Universities of Bristol and Exeter and teams from Australia) are now using the sounds of healthy reefs to help bring degraded ones back to life.
‘We’ve been studying sound on coral reefs for many years now,’ says lead author of the new study, Tim Gordon from the University of Exeter. ‘At first, we were looking to understand what the role of sound is in a natural, healthy coral reef. We were able to marvel at all of the different sound types that you can hear. The predominant thing is snapping shrimp, it’s this constant crackle like frying bacon or popcorn or static on the radio. And then if you listen really carefully, you’ll hear the noises of fish. They can be like a chatter or a chirp or a whoop or a growl – fish noises are almost as varied as birdsong.’
The researchers have been able to identify the ways in which fish use sounds to navigate and to locate coral reefs on which to settle. This is important from the perspective of conservation because while reefs are vital for many fish, the fish are also vital for the survival of coral. If they could be drawn back to degraded reefs via sound, they might help them recover in a number of ways, from cleaning away over-abundant seaweed to recycling and depositing nutrients.
This was put to the test by recording the noise of healthy reefs using special hydrosonic recorders. The team then took rubble from a particularly degraded patch of the Great Barrier Reef and created 33 new test sites. On some of these sites they played the healthy noises (using the same loudspeakers employed by synchronised swimmers), while others remained silent. The results showed that twice as many fish arrived, and stayed, on the noisy patches compared to the silent ones.
This technique could now be scaled up and used in conjunction with other coral restoration methods to attract fish back to degraded areas. But while it’s an exciting development in reef restoration, it’s still only part of the solution. ‘Reef restoration creates a couple of small pockets of survival that potentially re-seed a recovery later on,’ says Gordon. ‘But if we’re serious about saving coral reefs on a global scale, then we have to address the initial problems. We have to sort out climate change, overfishing and water pollution.’
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