Oysters Use Sound to Select Their Home, Study Suggests

Oysters may rely on sound when selecting the reef they will settle in for the rest of their lives, a new study suggests.

In their youth, oysters are free spirits, drifting wherever the current may take them. Part of that is simply because they don't have much of a choice: larval oysters can't swim against or across currents, though they are able to move up and down within the column of water they inhabit As they age, however, they develop a muscular "foot" that allows them to sense their environment and they begin to look for a reef to settle down in. The moment they find the right spot, they attach themselves, remaining there throughout their lives.

What intrigued researcher Ashlee Lillis, a North Carolina State University Ph.D. candidate, the mystery as to how the oysters select their home. Despite knowing that oysters are able to respond to some chemical and physical signals, Lillis grew suspicious that sound might play a role.

"When you're as small as these larvae, even if you're only 10 or 15 feet up in a water column you wouldn't have any real sense of where you were in terms of the seafloor beneath you," Lillis said. "But an ocean reef has very loud, distinct sounds associated with it. They're noisy enough to be heard by scuba divers and snorkelers. Even though oysters don't have ears and hear like we do, they might be able to sense the vibration from the sounds of the reef."

To test this hypothesis, she teamed up with David Eggleston, a professor of marine sciences, and geophysicist Del Bohnenstiehl to make underwater sound recordings of oyster reefs and the open seafloor. Together they then tested larval oysters both in the wild and the lab and found an increased settlement both in the lab and wild when the oysters were exposed to eef sounds.

"The ocean has different soundscapes, just like on land," Lillis said. "Living in a reef is like living in a busy urban area: there are a lot of residents, a lot of activity and a lot of noise. By comparison, the seafloor is more like living in the quiet countryside.

"This research is the first step in establishing what normal, healthy reef environments sound like," she added. "If we can figure out how the noise impacts oysters it may give us strategies for establishing new oyster beds. It might also give us a noninvasive method for keeping tabs on the health of our undersea reefs."