In the water industry we often discuss the topic of acoustic monitoring in the context of leak detection. However, acoustic sensors are being used today for a multitude of other applications. One of the more intriguing uses is as an underwater listening device to determine the vitality of coastal ecosystems.
The snapping of shrimp and the croaks and murmurs of fish produce an underwater orchestra in healthy ecosystems. However, marine environments around the world face a number of damaging anthropogenic influences. Because underwater soundscapes carry information about habitat quality, they can be used to determine the impacts of these pressures. In fact, a variety of studies have linked acoustic changes to ocean acidification, nutrient pollution, and over-fishing.
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In one 2016 study, researchers recorded four marine protected areas and four unprotected areas along the coast of the island Moorea, French Polynesia. Divers also counted fish, identified species, and measured coral cover in an effort to determine whether acoustic measurements were linked to healthier coral reefs.
They found that sites with more coral cover were, in fact, louder and areas with richer biodiversity produced more complex choruses with a wider variety of sounds. “You can, of course, hear the difference,” Frédéric Bertucci, a bioacoustician at the Insular Research Center and Environment Observatory in Perpignan, France, told Ensia author Roberta Kwok. “Reefs in good condition are really noisy.”
To test this theory, Katherine Indeckm a marine ecologist at the University of Queensland in Australia, studied recordings collected between the Gulf of Mexico and Tampa Bay, Florida. Some of the sound files were collected in 2005 during a toxic algae bloom. Others were recorded in 2013, after the ecosystem had begun to recover. During the algae bloom, Indeckm noticed that the recordings were nearly silent, but as the ecosystem regained vitality, the sounds became increasingly loud.
Traditional monitoring involves visual surveys performed by divers that scan these ecosystems, but this method is time-consuming and can disrupt reef life. Plus, visibility can interfere. The installation of underwater microphones could allow researchers to collect data for months, even in murky underwater environments.
Rather than listening for leaks in a water delivery system, this acoustic monitoring technology is being used to record the steady noise of an ecosystem and evaluate its health, as sudden silence could indicate environmental damage. What other acoustic monitoring applications can you imagine?