Coral reefs are in trouble. Overfishing, global warming, coral bleaching, and ocean acidification all play a part, among other factors. Degraded reefs sound — even smell — less attractive to fish. Many conservation and rehabilitation efforts exist to inhibit and attempt to reverse the degradation of global coral-reef systems. Recently a team of researchers found a new way to attract fish life to degraded reefs, which led to the improved health of these reef systems.
Juvenile fish spend their larval stages in the open ocean. They then use a number of sensory cues to find their way to healthy reefs, which then become their home. Damaged reefs smell and sound less attractive than healthy reefs, thus attracting fewer juvenile fish.
The sound of healthy reefs
Researcher Timothy Gordon and a colleague played sounds usually made by healthy reef systems and found that more juvenile fish settled nearby. The researchers played these sounds during sunset and sunrise around an area of the Great Barrier Reef which consisted of coral-rubble patch reefs. The coral in the area had experienced mass-bleaching and mortality in the two years before the research – more than 60 percent of coral was bleached.
The researchers measured the volume of fish settling in this area and compared it with an area on the reef with no sound was playing, as well as an area on the reef where they had set up ‘dummy’ speakers.
During the 40 days of the experiment (conducted between November and December 2017) the researchers found that more fish settled where the sound was playing compared to the soundless reef and the reef with the dummy speakers.
After 40 days, twice as many juvenile damselfish inhabited the reef where the sound was playing. The results were similar for all species of fish, with larger numbers of herbivores, omnivores, planktivores, invertivores and piscivores on the reefs where the researchers played sound as opposed to those with no sound.
Besides attracting more fish, these sound-enhanced reefs also attracted 50 percent more diverse species of fish. Researchers suggest that, while these sound-enhanced reefs initially attract juvenile fish, other fish might migrate to these reefs as the entire fish community becomes healthier.
This experiment did not investigate whether certain (isolated) sounds would attract settlement-stage fishes. It did, however, find that the sound of healthy reef systems is more efficient at attracting marine life than the sound of degraded reef and white noise.
The researchers concluded that playing sounds of healthy reef systems could work in conjunction with other coral-reef restoration efforts.
With global warming and other factors increasingly causing damage to reef systems the world over, we must look for more and more inventive ways to foster sustainability, rehabilitation and conservation. Playing the sound of healthy reef systems could be a valuable tool in this fight.