Study finds that listening to snapping shrimp is an effective tool to monitor coral reef health

Ithaca, N.Y. — High-frequency sounds produced by snapping shrimp, particularly at night, can serve as an effective indicator of coral reef resilience, according to new research published in the journal Royal Society Open Science.

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. The goal—determine if underwater acoustic monitoring can be used to assess whether marine protected areas are more resilient to coral bleaching events.  

The research team employed underwater microphones to listen to the reef and conducted visual surveys for fish and bottom-dwelling organisms. Unlike previous studies, this team looked at sounds using marine specific metrics and compared reef health before and after bleaching in addition to protection status. 

“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. 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,” said lead author Xavier Raick, postdoctoral fellow at the K. Lisa Yang Center for Conservation Bioacoustics at the Cornell Lab of Ornithology. 

The team found that 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.

The study recommends incorporating acoustic monitoring into long-term reef management programs, as it provides an efficient, non-invasive way to assess reef health alongside traditional visual surveys.

This method offers several advantages over traditional monitoring approaches that rely on daytime scuba diving surveys. 

"For managers, using these high frequency sounds made by snapping shrimps is a very interesting tool,” said Raick. ”For the moment, people are conducting scuba diving surveys only during the daytime, not during the night, because getting reliable data during night scuba diving is challenging. And it's quite expensive, and you only have a very small snapshot." 

The research revealed that these tiny crustaceans are highly dependent on coral health. 

"Many of these very small snapping shrimp need the corals to survive. If they don't have the corals, they could disappear. So it's really a high correlation between the coral's health and the snapping shrimp's abundance," Raick noted.

While the findings are significant, Raick emphasized that more research is needed across different locations: "It's a story on one island and needs to be repeated in other parts of the world."