Snapping Shrimp: Noisy Habits Indicate Reef Health, Study Shows

A snapping shrimp's signature claw tricks may be more than just a defense mechanism. A new study suggests the species' noisy habits may actually be useful when assessing the health of an oyster reef located in North Carolina's Pamlico Sound.

Snapping shrimp are primarily found in reef environments, similar to the one in the Pamlico Sound. These shrimp can rapidly "snap" their claws shut, at a speed of about 60 miles per hour, which makes a loud snapping sound, according to a news release.

Researchers from North Carolina State University spent an entire year recording sound samples from the oyster reef in an attempt to better understand how they may benefit the underwater ecosystem.

"We're not the only ones interested in reef sounds," Del Bohnenstiehl, one of the study researchers and a professor of marine, earth and atmospheric sciences at NC State, said the release. "But until now no one had sound samples from more than a couple of days or weeks at a time. If we're really going to explore the effects of sound on reef habitats and what that means, we need a longer sample."

The natural background noise along a reef plays a key role in helping organisms, including larvae, orient themselves, former NC State graduate student Ashlee Lillis explained.

Although the year's worth of recording have provided researchers with valuable insight, their findings contradict earlier assumptions about the behavior of snapping shrimp being fairly constant.

"There are seasonal differences in the level of sound, as well as differences between night and day," Bohnenstiehl explained. "In the summertime, we got up to 2,000 snaps per minute - in the winter, it was 100 or fewer. The overall impact in terms of noise emanating from the reef is a difference of 15 decibels between seasons. We also found that the shrimp were more active at night during the summer, but more active during the daytime throughout the winter months."

Their sound recordings also revealed the shrimp are able to respond very quickly to temperature change. This was evident in the different snap numbers recorded between the summer of 2011, when they began sampling, and the summer of 2012. Therefore, their findings have implications for understanding how diverse reef species are impacted by environmental changes. For instance, if the shrimp snap less, thus producing less noise, it could indicate poor health.

"The data raises a lot of questions," Bohnenstiehl added in the university's release. "For instance, some research has proposed that the noise of the reef helps migrating fish navigate. But if the sound really drops off in the winter, does this still work? And could the difference in snap numbers between the summers be affected by water quality as well as temperature? This work highlights how little we know, and how important long-term acoustic sampling is in terms of understanding the marine soundscape."

The study was recently published in the journal PLOS ONE.

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