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Shhhh! Baby oysters are always listening

By Reid Creager
Correspondent
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  • http://media.charlotteobserver.com/smedia/2014/03/12/21/14/h11k7.Em.138.jpeg|316
    - COURTESY OF RETO MUELLER
  • http://media.charlotteobserver.com/smedia/2014/03/12/21/14/1slkvb.Em.138.jpeg|386
    - COURTESY OF ASHLEE LILLIS

More Information

  • 10 pearls of oyster trivia

    • The city of Crisfield, Md., is built on a foundation of oyster shells.

     

    • Oysters produce very few pearls naturally, with just one of 10,000 animals producing a pearl in the wild. Most pearls created by these mollusks begin with human intervention when pieces of shells or beads are inserted inside an oyster.

     

    • The Romans first cultivated oysters more than 2,000 years ago.

     

    • Because of oysters’ tradition as an aphrodisiac, King Henri IV of France was said to eat 400 of them before dinner. The famous 18th-century lover Casanova would eat 50 with breakfast.

     

    • The Gulf Coast region, led by Louisiana, leads the U.S. in oyster production.

     

    Sonya Thomas, an American woman weighing less than 100 pounds, ate 46 dozen oysters in 10 minutes for the world record at a 2005 competition in – where else? – Louisiana.

     

    • Though the Pacific oyster (Crassostrea gigas) accounts for less than 25 percent of the U.S. production, it accounts for more than 75 percent of Europe’s oyster production.

     

    • Depending on the type, it takes between nine months and seven years for oysters to grow to market size.

     

    • Though their average life span is estimated at one to three years, oysters can live 20 to 30 years if undisturbed.

     

    • What’s billed as “the world’s only oyster museum” is on Chincoteague Island, Va.

    Reid Creager

    Sources: Pacific Seafood Group, The Experiences Blog, ESPN.com, Yahoo!


  • Reviving oyster harvests in N.C. and elsewhere

    In 1902, 800,000 bushels of Eastern oysters – the species indigenous to North Carolina – were harvested in the state’s waters. By 1994, that number plummeted to a record low of 35,000 due to pollution, disease, habitat loss, and a decline in water quality and fisheries, according to the North Carolina Coastal Federation.

    A number of organized efforts to restore water quality and habitats have gained momentum in the last couple of decades. An aquaculture process of cultivating oysters in cages and bags is underway after spectacular successes in Virginia during the past 10 years.

    North Carolina’s oyster rebound will take time, as it will in many other places worldwide that are employing new strategies to preserve and rebuild these environments.

    “All over the world, oysters and lots of commercial fisheries landings are at historic lows,” said Lillis. “In North Carolina, different fisheries have put a lot of effort into trying to restore and improve harvests. There are a ton of people in North Carolina working on oysters. …

    “This species is really important as a keystone habitat builder. So anything we know about them could be really significant in efforts to restore habitats, improve the aquaculture of oysters or just understand more how they end up where they end up.”

    Reid Creager


  • Meet a scientist

    Name: Ashlee Lillis.

    Age: 30.

    Lives in: Raleigh.

    Occupation: Postdoctoral research scholar.

    Hobbies: Ultimate Frisbee, traveling, scuba diving.

    Favorite oyster dish: Oyster fritters.

    Favorite quote: “The best way to observe a fish is to become a fish.” -Jacques Cousteau.


We need oysters, and not just to improve our moods.

The types we eat are among the most nutritious foods – rich in protein, zinc, iron, calcium, vitamins A and B. Oysters provide a habitat to serve and feed other sea creatures; their reef structures stabilize shorelines; and each of the mollusks can filter 40 to 60 gallons of seawater a day.

Now there’s new potential to learn more about oysters and ocean reef environments. For the past four years, Ashlee Lillis, a Ph.D. candidate in marine science at N.C. State, has literally dived into a little-explored aspect of oyster settlement: how the sounds of an undersea ocean reef can attract larval (baby) oysters to a permanent home.

To her knowledge, “no one works with effects of sound on oyster larvae,” said Lillis, the project’s lead researcher. “The other work being done is all in coral reefs and on fish. So no one in this country or hemisphere is looking at the influence of sound on marine invertebrates.”

She said her team found an increased settlement rate – in both the laboratory and the wild – when the larvae were exposed to reef sounds. Determining precisely how the noise affects the baby oysters could lead to strategies for establishing new oyster beds, she said, as well as for monitoring the health of the undersea reefs.

“One of the things we’re interested in is, what is a healthy soundscape versus an unhealthy soundscape, and then, does that matter?” she said.

The oyster crawl

Oyster larvae are so small that a million can fit in a human hand. So they can’t swim across or against currents, but they can move up and down within columns of water. As they mature, they grow a “foot” that helps them feel for the ocean floor terrain.

“One of the things they’ll do is crawl around, and if the texture is appropriate, that might be where they’ll attach,” Lillis said. “They often settle on something hard, like other oyster shells.”

Finding the right landing spot is difficult for the little critters.

“Oysters and other animals that need to attach to a hard substrate or hard bottom have a particular challenge in that way because these habitats, such as oyster reefs, or in tropical systems coral reefs, are not widespread,” she said. “The larvae are potentially transported far from where they were hatched, and across large areas that are just sand or mud without appropriate settlement structure.

“Because the suitable areas in which these organisms need to settle are patchily distributed, but they disperse over many kilometers of unsuitable habitat, they have adaptations to help increase their chances of encounter with adult habitat. Responding to sounds associated with adult habitat might be one of them – as suggested by my study – and larvae are also known to use other cues such as turbulence, chemicals exuded by adults, and water properties to give them information about the environment as they are transported around by the currents.”

Testing the theory

The sounds of an undersea ocean reef are loud, like a busy city. Lillis hypothesized that if this environment is noisy enough to be heard by scuba divers and snorkelers, there might be enough vibration to affect the larvae – even though oysters don’t have ears and can’t hear sound, per se.

With help from her adviser David Eggleston, professor of marine sciences, and N.C. State geophysicist Del Bohnenstiehl, she made underwater sound recordings of the louder oyster reefs and the quiet open seafloor.

“We use what’s called a hydrophone, which is an underwater microphone,” Lillis said. “It’s attached to an acoustic recorder and then can be anything from a digital hand-held recorder that journalists may use. There are some more sophisticated long-term recorders that will take recordings at scheduled times, so we can leave those out a little bit longer.

“So we deploy these usually when scuba diving and (attach) them to the seafloor. … We’ve also had some drifting hydrophone studies, which are very interesting, to see how the sound changes as the recorder moves through the environment. There are lots of ways to do it, but the basic technology is a hydrophone and a recorder.”

Then they tested these oysters in the laboratory and in the wild to determine whether settlement rates increased when they were exposed to reef sounds versus those from farther out. They found the larval oysters preferred settling in substrates with the reef sounds.

Learning and educating

Growing interest in Lillis’ research is reflected in grants she has received. There were none at first, she said, but then “we had several small awards to me early on from the National Shellfish Reef Association. Also, the American Academy of Underwater Scientists gave me a small grant for the pilot work.

“Then once we had some good data, we received a larger National Science Foundation grant. That’s what we’re using now to continue for the next couple years to do some extensions of what I did for my Ph.D.”

Many questions remain. Besides determining what’s a healthy soundscape and what’s not, it’s not known precisely which sounds oyster larvae are attracted to, or whether human noise (such as from boat engines) affects oyster reefs.

Meanwhile, Lillis works to educate the public outside of the science community via a cartoon website that she developed with an illustrator: http://bit.ly/1oJsBDi. “It’s an attempt to do some public outreach and explain some of these concepts in a simpler way,” she said.

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