Degradation, be it from coral bleaching or disease, drastically alters the vibrant ecosystem of a reef, leading to diminished biodiversity and a muted soundscape. However, recent studies conducted by the Woods Hole Oceanographic Institution suggest that sound may hold the key to coral reef restoration efforts.
The cacophony of a thriving coral reef, filled with the chirps, hums, and crackles of its diverse inhabitants, serves as more than mere background noise. Scientists hypothesize that these sounds play a crucial role in guiding coral larvae to suitable habitats for settlement and growth.
Harnessing this understanding, researchers experimented with broadcasting recordings of healthy reef soundscapes onto damaged or depleted reefs. Their findings, detailed in a recent publication in Royal Society Open Science, revealed a remarkable outcome: coral larvae exhibited a significant preference for settling in areas where these sounds were played, with settlement rates increasing by up to sevenfold compared to areas without the sound intervention.
This groundbreaking research underscores the potential of sound as a powerful tool in the restoration of coral reefs, offering a promising avenue for replenishing these vital ecosystems and safeguarding their biodiversity for the future.
“What we’re showing is that you can actively induce coral settlement by playing sounds,” said Nadège Aoki, a doctoral candidate at WHOI and the first author on the paper.
“You can go to a reef that is degraded in some way and add in the sounds of biological activity from a healthy reef, potentially helping this really important step in the coral life cycle.”
Once corals reach adulthood, they remain stationary, making their larval stage crucial for choosing a suitable habitat. During this stage, they navigate through currents, aiming to find optimal conditions to anchor onto the seabed. While past studies highlighted the impact of chemical and light cues on this process, Aoki and her team reveal that the soundscape significantly influences coral settlement locations.
In 2022, researchers conducted a replicated experiment in the U.S. Virgin Islands, focusing on Porites astreoides, commonly known as mustard hill coral due to its distinctive lumpy shape and yellow hue. This resilient species was chosen for its adaptability to varying environmental conditions. The experiment entailed the collection of coral larvae, which were then distributed into cups strategically positioned at three distinct reefs along the southern coast of St. John.
Among the selected reefs, Tektite stood out as relatively healthy, contrasting with the more degraded conditions observed at Cocoloba and Salt Pond, characterized by sparse coral cover and diminished fish populations.
At Salt Pond, a notable intervention was introduced by Aoki and her team, involving the installation of an underwater speaker system. Cups containing coral larvae were strategically placed at varying distances from the speakers: one, five, 10, and 30 meters. Over the course of three nights, the researchers broadcasted recordings of healthy reef sounds, previously captured at Tektite in 2013. Meanwhile, similar setups were arranged at Cocoloba and Tektite but without the introduction of any sound stimuli.
Upon retrieval of the cups, a striking observation emerged: a significantly higher number of coral larvae had settled at Salt Pond compared to the other two reefs. Notably, the larvae exhibited settlement rates averaging 1.7 times higher, with some instances reaching up to seven times the settlement rates observed elsewhere. Remarkably, even cups positioned 30 meters away from the speakers at Salt Pond surpassed the settlement rates observed at Cocoloba and Tektite.
Moreover, the data revealed an intriguing trend: the highest settlement rates were recorded at a distance of five meters from the speakers. However, even cups placed 30 meters away exhibited greater larval settlement compared to counterparts at Cocoloba and Tektite. This underscores the profound impact of the enriched sound environment on coral larval settlement, suggesting a potential avenue for reef restoration and conservation efforts.
“The fact that settlement is consistently decreasing with distance from the speaker, when all else is kept constant, is particularly important because it shows that these changes are due to the added sound and not other factors,” Aran Mooney, a marine biologist at WHOI and the lead author on the paper, stated.
“This gives us a new tool in the toolbox for potentially rebuilding a reef.”
Incorporating the audio could also be quite straightforward to execute.
“Replicating an acoustic environment is actually quite easy compared to replicating the reef chemical and microbial cues which also play a role in where corals choose to settle,” said Amy Apprill, a microbial ecologist at WHOI and a co-author on the paper.
“It appears to be one of the most scalable tools that can be applied to rebuild reefs, so we’re really excited about that potential.”
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