The sound of coral reef recovery

Croaks, moans, purrs, growls, foghorns, whoops, grunts... these are just some of the many sounds that are heard coming from a healthy and diverse coral reef.

Researchers, who wanted to find out just how healthy restored reefs can be, focused on parts of reefs in Indonesia previously destroyed by blast fishing. The areas were restored through the Mars Coral Reef Restoration Project for years preceding the study.

By taking one-hour acoustic recordings of various habitats, the scientists found that the restored habitats have become almost just as vibrant as those that are naturally healthy, while degraded reefs, in comparison, were rather silent. 

Noisy is good

On healthy reefs, a wide range of soniferous fishes and invertebrates contribute to a loud and diverse soundscape that plays an important role in ecosystem functioning, and acoustic cues in the soundscape guide the recruitment and settlement behaviours of many juvenile reef organisms that spend their larval stage in the open ocean.

The specific organisms responsible for making the sounds driving these patterns are unknown. Some of the sound types described in the new study have been previously described. For example, a range of percussive and pulse-train sounds have been associated with triggerfish (family Balistidae), damselfish (Pomacentridae) and butterflyfish (Chaetodontidae); growl and grunt sounds have been associated with soldierfish (Holocentridae); scraping sounds have been associated with the feeding of macroherbivores such as parrotfish (Scaridae) and triggerfish (Balistidae); and whooping sounds have been associated with the Ambon damselfish, Pomacentrus amboinensis.

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Bizarre sounds

However, other sound types are less familiar. For example, the researchers were not aware of any previous descriptions of the "laugh" sound. Each individual sound type does not necessarily correspond to a single sound-producing species; some fishes are capable of multiple phonation types and may be making more than one of the sounds described in this study.

Professor Steve Simpson of the University of Bristol said some of the sounds they heard were "really bizarre, and new to us as scientists." 

Importance

The recovery of soundscapes suggests that restored reefs have the potential to regain their attractiveness to settlement-stage organisms. This is encouraging as it means that restored reefs may have the capacity to attract future generations of reef organisms, improving the prospects of long-term ecosystem stability. These results are important because they demonstrate that active restoration of coral cover can have beneficial impacts on the wider reef ecosystem.