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2005
Volume 4, Number 3
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Can Oysters
Thrive Again?
Modelers
Confront
the Bay's
Complexity

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A Model Epic in Two Volumes

If the craft of a modeler can be compared to that of a writer, then the model itself could be considered an elaborate work of literary nonfiction. In the case of the oyster model, this work would read like an epic in two parts. North's larval transport model would be Volume I, the story of oysters coming-of-age. Volume II would follow the oyster and its progeny and its progeny's progeny ten years into the future. Other scientists will write this tale, technically known as the juvenile-adult demographic model.

In the opening chapter of Volume I, hydrodynamics — the Chesapeake's currents and tides — drive the plot. These forces determine the large-scale movement of oyster larvae of two species (native and non-native) over a three-week period, from spawning to settlementÂ.

After hydrodynamics set the stage in Chapter 1, the oyster larva emerges as the central character of Chapter 2. Here a particle-tracking model takes information from the hydrodynamic chapter on currents and salinity and projects where in the Bay larvae will move during their journey. Though larvae in the wild begin to swim vertically, the comÂputer's particle-tracking routine at this stage treats them as passive particles, entirely at the mercy of water, wind and waves.

By Chapter 3, however, the model begins to account for oyster biology and the larvae develop depth and complexity. Mimicking real life, they are no longer passive particles, but acquire attributes of age, swimming speed and behavior. That is, virtual larvae are now able — like real larvae — to direct their movementsÂ.

Chapter 4, the denouement of the larval oyster's "settle or die" drama, brings all of the plot lines together to make predictions about the potential distribution of larvae, both the native and non-native species. The pieces (hydrodynamics, particle-tracking and behavior) link together mathematically to generate maps of the Bay that forecast the distribution of each species (see graphic on page 8).

Later, North's maps will feed into another model developed by her collaboratorsÂ, statistician Mary Christman of the University of Florida in Gainesville and quantitative ecologist Jon V¿lstad from Versar, a science and technology consulting company. Volume II is a sequel of sorts. This so-called juvenile/adult demographic model will make predictions about what will happen as the oysters grow, reproduce, and die over the next ten years — projecting populations of the two species into the year 2015.

The outputs of Volumes I and II of the epic — the larval transport and the juvenile/adult demographic model — will generate maps that predict the potential distribution and abundance of the native and non-native oyster in the year 2015. These results will feed directly into policy makers' evaluations of the different restoration scenarios, providing one tool of many to assist them in making a final decision (see When Science Meets Policy).

Elizabeth North in a Tai-Chi pose - by Erica Goldman

Balance and form are everything in the ancient art of Tai-chi. Here researcher Elizabeth North works through a series of 108 poses to sharpen her concentration and focus — attributes she finds equally valuable in her scientific work. Photograph by Erica Goldman.

In the Public Eye

It's 5 p.m. on Monday. The day doesn't usually end so early for North, who puts her computer to sleep, picks up her gym bag, and leaves her office. This is the one day each week that she leaves work behind at a reasonable hour. She drives over to the Aquaculture and Restoration Ecology Laboratory, a new building on the Horn Point campus, to teach a class. She moves the tables out of the spacious lobby so that her students will have space to spread out across the floor.

Soon a small group of regulars arrive in the lobby and take off their shoes and socks. Several older women join a couple of graduate students at the lab for North's weekly Tai-chi instruction, their camaraderie evident as they fill each other in on the week gone by. Sitting in a circle on the floor, North begins to lead the group in a series of warm-up stretches, limbering up for the challenging poses to follow.

Class begins and North guides her students through a sequence of moves that they learned in the last session. She concentrates intently on her own form and balance, while providing tips to the class on how to improve technique. To become fluent in the full practice of Tai-chi can take years of study and practice and most of her students have only recently begun.

North's own practice of this ancient Chinese art form has evolved over the past 19 years, drawing from her skills in dance and her interest in Eastern philosophies, born of her studies of comparative religion. She takes Tai-chi, a powerful tool for mind-body relaxation, very seriously, participating in retreats and classes taught by masters of the art whenever possible.

When the class finishes the steps that they know, North goes through the complete sequence of 108 exercises on her own, while her students watch her form carefully. For this moment at least, North's mind and body are far away from models, oysters, and the pressures facing a young scientist in a political spotlight.

She anticipates the day when the spotlight may sharpen its glare in her direction, when the states of Maryland and Virginia issue the final decision on the oyster Environmental Impact Statement. She braces for the maelstrom of clashing worldviews that could hit, whatever the outcome. But for the most part, North works to make the larval transport model as iron clad as possible. She also reaches out to colleagues for advice and builds support in the academic community for her modeling efforts through seminars and presentations at national meetings.

Now that the Department of Natural Resources has provided updated maps of currently available oyster habitat, North can begin the final runs of her model. Her computer will run day and night to generate maps that show where the two species of oysters could distribute in the Bay to feed into the projections of the demographic model. Soon DNR will ask North to present her results at their headquarters in Annapolis in what will be the fourth in a series of public meetings, held to keep the EIS process transparent and open to all interested stakeholders.

North knows that communicating the idea of "model as tool" to the public could be challenging. "People get angry at weathermen when the 7-day forecast is wrong and this is a 10-year playing field. These are not predictions of what is going to happen," she says, only what could happen. She also realizes that her findings will likely face intense scientific, public, and possibly political scrutiny.

"It is scary and it is great. I like being involved. I like the idea that the tools I am developing are going to be useful," North says.

She has spoken with other scientists about how to insulate herself from the high profile nature of the EIS project. A respected colleague advised her first and foremost to publish her model expeditiously in the academic literature, to vet it through the peer review process. "If this ends up in court, which it very well could," North recounts, "published papers will be important for credibility."

North has already written the framework for the manuscript she wants to publish. An outline sits in a file folder on her desk. She needs to complete the final model runs before she can write the Results and Discussion sections. But on the same day that she delivers her final report to the Department of Natural Resources, North plans to drop the manuscript in the mail.


For More Information

Elizabeth North's Web Page
    northweb.hpl.umces.edu/

Maryland DNR's Oyster InFocus
    www.dnr.state.md.us/dnrnews/infocus/oysters.asp

Maryland Sea Grant Oyster Node
    www.mdsg.umd.edu/oysters/

National Academy of Sciences Report on C. ariakensis
    www.nap.edu/books/0309090520/html/

Chesapeake Bay Program Scientific and Technical Advisory Committee information on C. ariakensis
    www.chesapeake.org/stac/ariakensis.html
    www.chesapeake.org/stac/stacpubs.html



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