Documentary sounds out baby coral breakthrough

The team released microscopic baby corals onto degraded areas of reef in the Maldives. Image: Peter Harrison

A world-first restoration project that uses recordings of fish sounds to attract baby corals onto reefs, features in BBC documentary series Our Changing Planet.

The collaboration between marine scientists and coral fertility experts from Australia’s South Cross University and the University of Bristol, UK, could prove a gamechanger for reef restoration.

South Cross University's Professor Peter Harrison and Bristol's Professor Steve Simpson tested coral larval reactions to various sound recordings, before releasing microscopic baby corals onto degraded areas of reef in the Maldives.

Harrison’s coral larval restoration technique, known as coral IVF, supports successful production by allowing larvae to develop in the safety of a floating nursery before release on degraded reefs.

For many years Simpson has been working on acoustic research to attract juvenile reef fish to settle on reefs. His most recent work has indicated that coral larvae, too, move towards the sound of a healthy reef.

"It was fascinating to see some coral larvae start to alter behaviour in response to sound recordings from healthy reefs."

Peter Harrison, South Cross University
Floating coral nursery pools in Maldives. Image: Peter Harrison

Remarkably, some fish vocalisations appear to trigger coral larvae to alter their swimming trajectory towards healthy reef sounds before sinking to the bottom to settle and grow.

The scientists joined forces for the first time in the Maldives in March 2023 as part of a research collaboration filmed exclusively by the BBC’s Natural History Unit.

Harrison said, “It was fascinating to see some of the coral larvae start to alter behaviour in response to sound recordings from healthy reefs that have rich acoustic soundscapes of fish and other organisms.

“Whereas recordings from badly degraded reefs with fewer fish and acoustic signals had no obvious effect on larval behaviour. This result is exciting as it offers a new pathway for enhancing coral and reef restoration to increase the scale of larval settlement through acoustic enrichment.”

n the Maldives: Peter Harrison with PBS host M Sanjayan and Steve Simpson. Image: Peter Harrison

Nine months later in Australia, the respective research teams followed-up with a controlled laboratory experiment at the Lizard Island Research Station, at the northern end of the Great Barrier Reef, in December 2023.

“Once again, the results showed that sound recorded from healthy reefs increased the rate of larval settlement, supporting the idea that sound may be an important trigger for larval settlement,” said Harrison.

Our Changing Planet series, available on BBC iPlayer in the UK and PBS in the US, charts the world's most threatened ecosystems over a period of seven years, offering a unique global portrait of extraordinary change and the hope of ground breaking solutions. The third series is Restoring Our Reefs.

Naturalist Steve Backshall hosts the series for the BBC, while in the US, M Sanjayan is the host.