The ocean is perceived to be a vast and quiet place, but this is not entirely accurate. Healthy coral reefs are naturally and remarkably noisy ecosystems, with a variety of marine organisms (including fish and invertebrates) all contributing to the underwater commotion.
The volume intensity and acoustic composition of a reef often relate to the diversity and abundance of its inhabitants and provide an indication of its overall condition. These sensory cues are used by larval stage reef fish to identify, orientate themselves towards, and settle on the reef habitat. This recruitment process is vital for establishing and sustaining healthy fish populations that perform important ecosystem functions and are a key aspect of minimising a reef's degradation.
(Image: CNN.com)
Once a reef has become degraded, its sound output diminishes in quality, becoming less attractive to settlement-stage fish and can lead to an overall decline in the reef's biodiversity and the likelihood of recovery. However, studies have shown that it is possible to restore a degraded reef's appeal through artificially imitating sensory cues projected by that of a healthy reef. Acoustic methods for artificial restoration via a technique called 'acoustic enrichment' have displayed effective results for promoting the settlement and retention of functionally important fish.
Using underwater loudspeakers, recordings taken at a healthy reef were projected at multiple locations consisting of dead coral rubble. The loudspeakers were floated directly above the centre of each rubble reef and positioned to ensure that the sound could be evenly circulated throughout the underwater surroundings.
Researcher positions an underwater loudspeaker on a coral reef
The study displayed that fish abundance across all the major feeding groups increased and demonstrated how acoustically enriched corals can increase a reefs detectability. These promising results, coupled with the ease of in-field operation, make acoustic enrichment an attractive prospect and a potentially powerful tool to help rebuild fish communities in unhealthy and stressed environments.
It should be noted that if used exclusively, such techniques will not work in the rehabilitation of coral reef systems and will need to be incorporated alongside simultaneous actions. If acoustic enrichment can be combined with active habitat restoration and effective conservation management, re-establishing fish populations through this technique could fast-track ecosystem revival and provide another string to the bow of reef recovery.
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