An Ear to the Ocean
Josh Pysanczyn
Coral reefs are subject to a growing array of human stressors: ocean acidification, global warming and destructive fishing practices, to name a few. But what about noise pollution? Josh delves into this often forgotten threat, and gives us a sneak peak into how sound is being used in conservation efforts.
Over the past decade, a growing field of research has shown that common human-made noises are impacting organisms across a range of taxa within the coral reef ecosystem. Interestingly, we are now looking into using ‘natural’ noises to help mitigate the effects of their anthropogenic counterparts.
How organisms use sounds on the reef
Both bony fish and crustaceans use sound to undertake a variety of behaviours. From pulsating courtship calls in domino damselfish, to the predatory snap of snapping shrimp; the ocean is filled with the ambient symphony of the coral reef.
This ambient sound communicates a message of its own. It acts as orientation cue, a homing signal so to speak, attracting settlement stage larvae of reef fish and decapod crustaceans acoustically navigating the oceans.
But what about coral larvae, can they detect and use ambient reef sounds? Well, not only have researchers shown that coral larvae, or planulae, use external cilia to detect and swim towards the sounds of coral reefs, but that they also prefer the hustle-and-bustle of louder, healthier reefs.
Noise pollution from motorboat traffic has been found to disrupt and stress coral reef fish as well as corals themselves. Photo: Unsplash.
Anthropogenic Noise Pollution
Since the 1950s, the cacophony of human activities like seismic surveying, oil drilling and boat engines, has become distinctly apparent. In 2019, a review discussing the impacts of these sounds on marine life suggested that between 1950 and 2000 the intensity of marine noise doubled every ten years.
Motorboat traffic is of particular concern due to its constant presence in coastal regions with high amounts of tourism, fishing and transportation. When exposed to motorboat noise coral reef fish become stressed and behave somewhat abnormally, resulting in disruptions to orientation behaviour and a significant increase in the likelihood of predation.
We now know that corals are also detrimentally affected by anthropogenic noise. The ability of coral planulae to detect ambient reef noise is hindered due to interferences from boat noise on nearby reefs, leading to reduced coral recruitment.
Conservation
As it stands, international measures aimed at systematically reducing the effects of anthropogenic noise pollution in areas where coral reefs are impacted, such as the International Maritime Organisation’s (IMO) ‘Voluntary Vessel-Quietening Guidelines’, are limited, poorly enforced, and non-mandatory.
Nonetheless, to help mitigate the effects of reef degradation, a growing international collaboration of locally run coral reef restoration projects such as Coral Gardeners, and multidisciplinary projects such as the Mars Assisted Reef Restoration System (MARRS) and SECORE International, are directing their efforts for the sake of one common interest: saving coral reefs.
Acoustic enrichment is a newly devised technique that hopes to restore coral reef communities back to health. Photo: Unsplash.
Acoustic Enrichment
With coral reefs increasingly threatened by anthropogenic stressors, the implementation of novel techniques in conjunction with existing measures is vital for their restoration. Acoustic enrichment is a newly developed method using recordings of healthy, noisy reefs broadcasted from loudspeakers on degraded reefs to entice the recruitment of fish communities.
Researchers from the UK and Australia wanted to test their newly devised technique on the northern coast of the Great Barrier Reef in the hopes that experimental patches of dead coral rubble could be brought back to life. Their results, published in Nature Communications, not only show that acoustic enrichment enhanced fish community development, but that the number of different species increased by 50% over six weeks.
It is currently unknown whether acoustic enrichment can be used as an effective tool for enhancing recruitment of settlement stage coral planulae to coral reefs. If shown to do so, the installation of acoustic enrichment facilities on degraded reefs around the world have the potential to be a serious asset in the active restoration of coral reef ecosystems.
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