Aran Mooney crouched on the bottom of a small boat, cradling a foot-long cylinder made of tough plastic mesh, and covered in stringy green algae. The cylinder contained an underwater recording device, and it had been sitting at the bottom of Tisbury Great Pond on Martha’s Vineyard for a month.
“Fingers crossed everything’s working,” said Mooney, a senior scientist at the Woods Hole Oceanographic Institution. “Now we’re going to go back to the lab and listen and see what this area sounds like.”
Mooney studies underwater acoustics, and he hopes the sounds recorded at the bottom of this pond will offer clues to help restore wild oysters.
“All sorts of animals use sound in a lot of different ways,” he said. The question is, “Can we use sound to help support New England oyster reefs?”
Wild oysters often live in craggy reefs, sort of like underwater cities. And much like Boston rings with the sound of “Sweet Caroline” and screechy subway cars, a reef emits its own soundscape — and oysters can recognize the sound of home.
Oysters don’t have ears, of course, but they sense sound waves with special hair cells on their gills and small balance organs called statocysts.
A few years back, scientists at North Carolina State University recorded the sound of their local oyster reefs. To the untrained ear, the reef sounds like bacon frying in a pan. Ask an expert, however, and recognize the sizzle as snapping shrimp, one of the loudest animals in the ocean.
When the North Carolina scientists played this sound underwater, swimming oyster larvae liked it. They settled to the bottom and stuck to oyster shells the researchers had placed in the water.
“We were basically tricking wild oyster larvae into settling on these shells, said David Eggleston, a professor of marine science at NC State who oversaw this research. The sound acted as a sort of “lighthouse,” he said, to guide the larvae.
“It’s a cue to say, ‘Hey, choose this spot,’ ” Mooney said. “ ‘Other oysters are succeeding here. This is where you want to be, too.’ ”
This “settlement” is a critical part of oyster development. Where oyster larvae settle down can determine whether they live or die. Land on some existing oyster shell and you might survive; land in a barren mud flat and you’re toast.
Mooney heard about the research on oysters in North Carolina, as well as experiments on different oyster species with sound from Australia and the North Sea. He and others have also done similar work on tropical coral reefs. He wondered if sound could help oysters in New England.
The New England coast used to be crowded with wild oyster reefs. When healthy, the reefs provide huge ecological benefits. The oysters clean the water, the reef provides habitat for valuable commercial fish and protects the coast during storms. But the reefs have been decimated by overharvesting, pollution, development and climate change.
While wild oysters still exist in scattered beds, the huge oyster reefs that once supported rich biodiversity are now largely absent in Massachusetts, according to the state’s Division of Marine Fisheries. It is estimated that more than 99% of historic oyster reef habitat has been lost in New England.
There are many efforts underway to restore the reefs in Massachusetts. But getting oyster larvae to settle in the right place at the right time can come down to luck; the larvae are poor swimmers and can be led astray by waves and currents.
Maybe, thought Mooney, playing those North Carolina reef sounds could guide them.
The oysters that live in New England and North Carolina are the same species: the Eastern Oyster. But the regions’ underwater soundscapes are different; it’s unclear if Massachusetts oysters would like North Carolina sounds.
“We don’t have those snapping shrimp. We have different species of fish,” Mooney said. “Are the oysters here going to respond to sound in the same way?”
Eggleston put it differently.
“Well, our North Carolina accents are different from your New England accents,” he said. “So we’ll just see if that also applies to oyster reefs.”
Dubious stuff that sometimes works
Mooney isn’t sure what healthy oyster reefs sound like in New England. Because, as far as he can tell, nobody has recorded them. That’s what led him to Tisbury Great Pond.
The team set underwater recorders at two spots in the pond for about a month. Local shellfish constables Will Diamond and Isaiah Scheffer helped the team choose sites with healthy oyster populations. Diamond seemed intrigued by Mooney’s work.
“I’m curious to see the data,” said Diamond, the shellfish constable for West Tisbury. He guessed the bottom would sound like “crinkling and crackling.” Maybe?
“I’m not sure what to expect,” he said.
Chilmark shellfish constable Scheffer seemed a bit more skeptical.
“ Some people are a little dubious about this,” he said, as Mooney’s research team unloaded gear from the boat.
Mooney smiled.
“ I’ve made my career out of doing dubious stuff that sometimes works,” he said.
The researchers will also collect sound from waters in Maine and Wellfleet, which have some healthy reefs, though not like they used to.
“Early explorers refused to enter Wellfleet Harbor because there was so much oyster reef sticking up out of the water that they thought it would jeopardize their vessels,” said Dan Goulart, a Coastal Project Manager for the Nature Conservancy in Massachusetts.
The group is working with towns and oyster farmers to restore several oyster reefs in the state, and Goulart is overseeing a project in Mashpee’s Hamblin Pond.
Wild oysters face a lot of challenges in New England: pollution, disease, climate change, invasive green crabs that eat baby oysters, and sponges that bore holes in their shells. Underwater sound will not be the silver bullet that saves them.
But Goulart is open to the possibility it offers.
“I’ll put underwater speakers out playing Mozart if it’ll help my reef grow,” he said.
The research “makes sense,” he added. When people hear music and laughter they gravitate towards it.
“I can imagine that it occurs underwater, and we’ve just been ignoring it,” he said.
What’s that rattling sound?
A couple days after the boat trip, Mooney listened to some of the sound picked up in the Martha’s Vineyard pond. There was wave noise, a little boat noise, and some weird rattling sounds. Mooney said that last bit was made by a common fish called a cusk eel.
Over the next two years, Mooney’s team — research associate Andria Salas and PhD candidate Audrey Sarin — will use these sounds, and others they find, for lab experiments.
Salas and Sarin will play sounds to oyster larvae swimming in tanks. The larvae will hear either local sounds, North Carolina sounds, or plain old gurgling fish tank sounds. They’ll measure what the larvae like best by counting how many settle into shells on the tank bottom.
“Does Massachusetts sound work better than North Carolina? Do either of them work? We don’t know,” said Mooney. “We don’t know if our oysters are deaf or don’t care about sounds, or they only want to hear Neil Diamond or what.
“The bottom line is that we don’t know, and that is the cool thing that we’re learning here.”
Mooney hopes his work will at least document the sounds of healthy New England oyster reefs, and allow people to assess a reef’s health by listening to it.
But he also has bigger ambitions for his work: he hopes it can lead to a New England “mixtape” of sorts, which oyster farmers could use to boost production, or reef restorers to make their work more efficient and successful. His job for now is to figure out the soundtrack.
This article was originally published on WBUR.org.
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