Underwater acoustic monitoring can be used to assess whether marine protected areas are more resilient to coral bleaching events
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A new study, published in the journal Royal Society Open Science, has revealed that high-frequency sounds produced by snapping shrimp, particularly at night, can be an effective indicator of coral reef resilience.
The study, led by an international team of researchers, examined underwater soundscapes of protected and unprotected coral reefs before and after two major coral bleaching events in 2016 and 2019 around Moorea Island – part of the French Polynesia’s Society Islands archipelago in the South Pacific.
Their goal was to determine if underwater acoustic monitoring can be used to assess whether marine protected areas are more resilient to coral bleaching events.
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By deploying underwater microphones – used to listen to the reef – and conducting visual surveys for fish and bottom-dwelling organisms, researchers were able to glean insight into the intricacies of how reefs work.
Unlike previous studies, the team looked at sounds using marine-specific metrics and compared reef health before and after bleaching.
‘What a lot of people do is compare a very damaged reef to a very pristine reef or they compare a marine protected area with an unprotected area,’ said postdoctoral fellow at the K. Lisa Yang Centre for Conservation Bioacoustics at the Cornell Lab of Ornithology and lead author, Xavier Raick.
‘But in this study, we wanted to work with more realistic data, and really study the resilience of coral reefs while taking into consideration the protection status of the reef and before and after a bleaching event,’ Raick continued.
Through their research, scientists found high-frequency sounds from snapping shrimp were more prominent in protected areas after bleaching compared to unprotected sites, suggesting that protection status can help reefs withstand climate impacts.
‘The high-frequency sounds, mainly during the night, of snapping shrimp can be used as a real indicator of coral resilience,’ said Raick.
‘Snapping shrimp’s abundance is a mirror of coral cover. So if you have more corals, especially very big colonies, you have more snapping shrimps, and then you can use their sound as a proxy for the reef, structure, and health,’ Raick explained.
In addition to these findings, the research also revealed how many of these snapping shrimp need corals to survive. If they do not have corals, the shrimp could entirely disappear – representing a high correlation between the coral’s health and the snapping shrimp’s abundance.
To assess reef health, researchers recommend incorporating such acoustic monitoring into future long-term reef management programmes. As well as this, researchers emphasise that more research across different areas of the world needs to be conducted to paint a clearer picture of the relationship between aquatic life and reefs.
Noisy equals good
In terms of a coral reef, the noisier it is, the better. Researchers say that a healthy reef has a complex, ‘crackling, campfire-like’ sound, while quieter reefs are typically those that are degraded.
Research has also shown how noise attract fish and crustaceans to reefs. During another study, when the recording of healthy reef sounds were played over compromised reefs in Australia, researchers found double as many fish settled into these reefs.
In addition, a study conducted in a degraded reef off the US Virgin Islands found that playing such sounds attracted up to seven times more coral larvae and fish than a decimated reef with no acoustic enrichment.
Despite these advancements in protecting coral reefs, many across the world are facing extreme threats such as coral bleaching. This occurs when water warms too much, causing corals to turn white and die. In turn, the marine life that lives on and around the reef faces a dying and decaying habitat.
