Acoustic Enrichment: a New Hope for Dying Coral Reefs?

Coral reefs protects land from coastal erosion, are vibrant biodiverity hotspots and important carbon sinks; sadly, rising ocean temperatures are causing them to die. Attracting new fish to degraded reefs could help them bounce back, and scientists have found a new way to do so. Here, we cover how acoustic enrichment could help restore dying coral reefs around them world. 

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Up to half of the world’s coral reefs have been already lost or severely degraded due to climate change, pollution, recreational tourism and overfishing. By 2050, almost all coral reefs in the world will be affected and up to 75% could face high to critical threat levels. 

There is no doubt that the biggest threat to coral reefs is climate change.  According to the National Oceanic and Atmospheric Association, between 2014 and 2017 around 75% of the world’s tropical coral reefs experienced heat-stress severe enough to trigger bleaching. The impacts of climate change could significantly alter the ecosystem of coral reefs so that the environmental conditions are no longer suitable for the survival of corals. For example, increasing sea surface temperatures, increasing ocean acidity and more ice meltwater could all result in severe coral degradation. 

Current coral reef conservation efforts are focused on establishing Marine Protected Areas (MPAs) and fishery management. These measures help but they don’t help restore reef systems that have already been degraded. A healthy coral reef buzzes with animal sounds, it is full of crackling, popping and grunting coming from fishes and other organisms that live there. In contrast, degraded coral reefs are almost silent which deters fishes away from the reef. Using a technique called “acoustic enrichment”, scientists were able to make the environment more attractive and bring new life to these ecosystems.

How does acoustic enrichment work? 

In a study published in nature communications, a group of international scientists from the UK and Australia have found that broadcasting the sounds of a healthy coral reef enhances fish community development in degraded coral reefs.

The study was carried out in the lagoon southwest of the lizard island in Australia where 60% of live corals were bleached due to a severe mass bleaching event leading to widespread ecosystem change. Each experimental reef was assigned one of three experimental treatments: no loudspeaker, a dummy loudspeaker system or a real loudspeaker system (acoustic enrichment). The experiment is then proceeded by playing sounds from healthy coral reefs in the experimental reefs for the entire night and measuring the number of fishes in each reef throughout the process.

Source: Gordon, T.A.C., Radford, A.N., Davidson, I.K. et al. Figure a. Number of fishes per reef over time. Figure b. Raw count data of the number of fishes per reef.

After 40 days of acoustic enrichment, there was a great increase in juvenile fish communities in the reef (blue curve). Damselfish, in particular, proliferated. These are common inhabitants in coral reefs and they largely rely on corals for the protection of their eggs before they hatch; the ammonium they excrete in turn stimulates coral growth.

Why is biodiversity important in coral reefs?

Generally, a highly biodiverse ecosystem inhabiting many different species is more resilient to changing environmental conditions and can better withstand significant disturbances (eg. climate change, pollution etc). Every species has its own niche, which is how a species contributes and interacts in its own ecosystem. When a coral reef inhabits a large number of species, it can imply some levels of functional redundancy where multiple species have similar niches so that if one species is lost, they can substitute for one another. In other words, the loss of one species will have a smaller effect in a diverse system compared to an ecosystem with limited species. To put a number on this, studies have shown that the productivity of low diversity systems decreased 50% more than highly diverse systems during extreme climatic events.

As climate change continues to exacerbate in the coming years, solutions like acoustic enrichment could become crucial to help restore degraded ecosystems. It goes to show that there are many strange, interesting and cost-effective ways to help our suffering biodiversity. 

This article was written by Rachel Yan. Cover photo by Hiroko Yoshii on Unsplash 

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