Listening to wildlife reveals ecosystem changes after hurricanes

When Ben Gottesman and his colleagues from Purdue University and the National Oceanic and Atmospheric Administration set up acoustic sensors in Puerto Rico, they wanted to see how acoustic signatures correlated with fish and other wildlife diversity.

What they didn’t know as they set up their monitoring sites — on the coastal gradient of the Guanica Dry Forest and on nearby coral reefs — was that two intense hurricanes would soon hit the island. When Hurricanes Irma and Maria arrived in September 2017, they would give them some unexpected insights into how sound-producing terrestrial and marine species responded to these storms.

“It gave us a really interesting window to test whether passive acoustic monitoring could help us better understand the ecological impacts of this type of disturbance,” said Gottesman, lead author of the recent research and PhD candidate at Purdue University’s Center for Global Soundscapes. He presented the findings presented at the American Geophysical Union’s Ocean Sciences Meeting in Portland, Oregon, last month. “One of the real benefits of passive acoustic monitoring stations is that you can obtain baseline data. Then, if a disturbance event occurs, you have that prior baseline information that you can use for a pre-post comparison.”

The research team found elevated noise levels due to wind during both storms, though fish choruses persisted through them. In fact, researchers observed an uptick in fish chorusing in the three days after Irma, which they believe may have have resulted from the increased turbidity that followed the storms. Fish generally prefer to chorus when it’s darker, Gottesman said, and the additional darkness likely resulted in more fish calls during courtship choruses.

Other species, however, were detected much less during the storm and following the storm. Snapping shrimp, which use snaps to stun their prey, were snapping less, Gottesman said, probably because intense storm conditions temporarily stopped them from seeking prey.

The storm also impacted terrestrial animals including bird and insect species. Bird choruses at dawn and insect calling at night decreased after Hurricane Maria, and these patterns continued for at least several weeks, which was more prolonged than the response of marine species, said Gottesman. “These findings could suggest that this dry forest coastal ecosystem was less resilient to the hurricanes than the adjacent coral reefs,” Gottesman said.

For Gottesman, the study shows how passive acoustic monitoring can allow researchers to learn more about an entire ecosystem response to an event, rather just a single species.

“Right now, as passive acoustic monitoring is becoming more common, this is a really compelling case study that demonstrates that this method can help us to better understand the impact of ecological disturbances, in water and on land.”

Header Image: A tree fell over in Puerto Rico’s Guanica Dry forest following Hurricane Irma. Researchers studied the affects of the hurricane on marine and terrestrial mammals through passive acoustic monitoring. Image courtesy of Ben Gottesman.