Underwater Reef 'Music' Attracts Young Fish to Degraded Coral

Attracting fish is the first step in regenerating damaged reefs.

diver and fish on Great Barrier Reef
Diver and fish on Great Barrier Reef, Queensland, Australia.

Bob Halstead / Getty Images

Coral reefs are in great distress, due to warming oceans that are causing corals to bleach and die. Conservationists are worried about how to save them, but a radical new study might come as music to their ears.

A team of scientists came up with the unusual idea to play underwater sounds along degraded portions of Australia's Great Barrier Reef that would replicate the usual noises heard on a healthy, active reef. When they did so, they found that fish were attracted to the music and more willing to hang around.

Dr. Stephen Simpson, a researcher at the University of Exeter, UK, and one of the study authors, said in a press release that "coral reefs are remarkably noisy places – the crackle of snapping shrimp and the whoops and grunts of fish combine to form a dazzling biological soundscape." 

These are the sounds young fish are attracted to, after they've hatched and spent their larval stage in the open ocean. But once a reef becomes degraded, it smells and sounds less attractive to the juvenile fish, who opt to settle elsewhere, thus speeding up further degradation of the reef. 

The scientists conducted their experiment at the Lizard Island Research Center in the northern Great Barrier Reef area. Prior to the study (which took place at the end of 2017), this area had experienced severe mass bleaching events, with 60% of live coral becoming bleached. 

bleached coral
An area of reef that experienced bleaching. XL Catlin Seaview Survey/The Ocean Agency (Richard Vevers) via 'Chasing Coral' documentary

Reefs were given one of three experimental treatments. They either had no loudspeaker, a dummy loudspeaker (to control for visual cues that might affect fish behaviors), or a real loudspeaker (a.k.a. "acoustic enrichment treatment") that played reef sounds. Playback occurred for 40 consecutive days, always at nighttime, which is when fish settlement typically occurs. 

At the end of the experiment period, the researchers found that acoustically-enriched reefs had attracted fish at a faster rate than non-enriched reefs. From the study: "After 40 days, there were twice as many juvenile damselfishes on acoustically enriched reefs than both categories of acoustically unmanipulated reefs, with no significant difference between the two control treatments." Biodiversity also increased by 50%, with more than just damselfishes attracted to the sound.

While the presence of fish alone cannot restore a coral reef to good health, study author Dr. Mark Meekan explained that "recovery is underpinned by fish that clean the reef and create space for corals to regrow." Acoustic enrichment could "facilitate a 'snowball effect', whereby other fishes respond positively to communities established earlier, causing further increases in settlement."

The researchers hope that this discovery can add to reef restoration efforts because, at this point, the reefs need all the help they can get. You can read the full study here, published in the journal Nature Communications.