Using underwater speakers to broadcast recordings of healthy coral reef ecosystems encourages fish to find and settle on damaged and man-made reefs.
The results of an experiment undertaken at Lizard Island, Queensland, show that playing the sounds of a healthy reef ecosystem is associated with higher rates of colonisation of man-made reefs by fish species, as compared to the rates seen at reefs where the sounds weren’t broadcast.
The study examined thirty-three man-made coral-rubble piles designed to approximate a reef structure. Eleven reefs included a broadcast speaker. The remaining ones were used as control groups, half with a dummy speaker and half without.
Over a forty day survey period the reefs with acoustic enrichment showed the highest rates of colonisation by damselfish (a common and abundant family of reef fishes), which remained in high abundance throughout the survey. After forty days damselfish were twice as abundant at enriched reefs as compared to the control group reefs.
At the end of the survey period, more juvenile fish were present at acoustically enriched reefs. The overall number of species was higher, and the developing fish communities more diverse.
This means that playing healthy reef sounds at a location attracted higher numbers and more varied species mixes of herbivorous, omnivorous, planktivorous, invertivorous and piscivorous fish.
The two control groups – reefs with dummy speakers and reefs without – showed no significant differences between each other for any of the survey measures.
It seems that new reefs are not colonised equally, and the appearance and added habitat diversity provided by a speaker doesn’t improve a reef’s attractiveness to fish.
Climate change and human-caused disturbance is triggering large-scale change to coral reefs around the world. The broad scale impact of coral bleaching events is particularly concerning to those who are tasked with managing and conserving the ecosystems.
Diverse fish assemblages help to maintain the overall health of coral reefs because they perform a variety of important functional processes. Having healthy fish populations gives a reef a better chance of staying healthy and recovering from damage.
The problem is that a damaged reef sounds less appealing to young fish looking for a place to live.
While smell is another important factor leading fish to new homes, it’s hard to efficiently replicate. Broadcasting the sounds of a healthy reef is much more practical for reef managers, and it’s a known attractant for a wide variety of juvenile fish.
It’s not known exactly how the broadcasted sounds affected the fish communities – whether they made the reefs easier to find or more attractive to settle on once the fish arrived; or a mix of both.
Regardless of the exact mechanism, it looks like broadcast speakers might be a useful tool in bringing fish back to damaged coral reefs.
This is likely to benefit wider areas than those immediately surrounding the loudspeakers, with fish forming small-scale communities that in turn create more niches for different species to fill; increased activity (sound and smell) helping to direct more fish to the area; and natural behaviours causing the residents and their offspring to migrate away from the original settlement area as they progress through their lifecycles.
Sound as a tool for ecosystem management is only a recent development. It has been used to affect the behaviour of some birds and mammals, and fish living in various fresh and marine environments show habitat selection influenced by sound.
Using sound to help manage coral reefs might guide new techniques for conserving various other aquatic systems where restoration projects are underway.