CHESAPEAKE QUARTERLY MARYLAND SEA GRANT COLLEGE • VOLUME … · College Park,Maryland 20740 301.405.7500,fax 301.314.5780 e-mail:[email protected] 8 The Culture of Disease A second

CHESAPEAKEQUARTERLYCHESAPEAKEQUARTERLY

MARYLAND SEA GRANT COLLEGE • VOLUME 5, NUMBER 1MARYLAND SEA GRANT COLLEGE • VOLUME 5, NUMBER 2

The MSX FilesUnmasking an

Oyster Killer

The MSX FilesUnmasking an

Oyster Killer

contents Volume 5, Number 2

Cover photo: Gene Burreson and Nancy Stokes read an X-ray film showing the sequence of akey section of the DNA of MSX, the parasite that devastated oyster populations in both Delawareand Chesapeake bays. Though X-ray films have now given way to computer screens, the earliertechnique provided a key to finally figuring out the probable origins of the MSX parasite.PHOTOGRAPH BY MICHAEL W. FINCHAM.

CHESAPEAKE QUARTERLY September 2006

Chesapeake Quarterly is published four times a year by the Maryland Sea Grant College for and about themarine research, education, and outreach community around the state.

This magazine is produced and funded by the Maryland Sea Grant College Program, which receives supportfrom the National Oceanic and Atmospheric Administration and the state of Maryland. Managing Editor andArt Director, Sandy Rodgers; Contributing Editors, Jack Greer and Michael Fincham; Science Writer, EricaGoldman. Send items for the magazine to:

Chesapeake QuarterlyMaryland Sea Grant College4321 Hartwick Road, Suite 300University System of MarylandCollege Park, Maryland 20740301.405.7500, fax 301.314.5780e-mail: [email protected]

8 The Culture of DiseaseA second parasite, Dermo,

now kills more oysters

than MSX, but molecular

technologies are beginning

to unlock its biological secrets.

14 The Missing LinkWhile researchers have finally identified MSX, they still don’t know how the disease is transmitted from oyster to oyster.

16 New Underwater Grasses GuideA new guide to submerged aquatic vegetation will help those interested in learning more about these important plants.

4 The Mystery Invasion of Chesapeake BayAlthough the fiftieth

anniversary of the appearance

of the oyster parasite MSX

is quickly approaching,

scientists have only recently

solved the mystery of

its origin.

T he bottom ofChesapeake Bay isa battleground lit-

tered with the emptyshells of dead oysters.Gone, for the most part,are the living oyster reefsthat once created habitatfor small fish and crabsand helped filter Baywaters now cloudy withexcess plankton.

Tongers and dredgersand police once fought overthose reefs in the infamousOyster Wars of the 19th and early 20thcenturies. But today the combatantsinclude watermen and oyster growers, sci-entists and state agencies and environmen-tal organizations.And the core battles ragenot over how to harvest the reefs, buthow best to rebuild them. Should wereplant the Bay with native oysters — orwith non-natives imported from China?

The answer may depend in part onanother question: what killed off the oys-ter reefs of the Chesapeake in the firstplace? The suspects include disease, over-fishing, sedimentation, habitat destruction,and water quality changes. Of all the well-known oyster killers, the most dramatic inrecent decades was MSX, an epidemicthat began in the late 1950s. An unknownparasite, MSX was a terrible swift sword,slashing harvests by 90 percent on theoyster grounds of Delaware Bay and by75 percent in the Virginia Chesapeake inits first three years.The result was disaster:an oyster-killing disease that altered theecology of two estuaries and nearly wipedout oyster industries in three states.

Where did this killer parasite comefrom? When Gene Burreson and NancyStokes of the Virginia Institute of MarineScience found a way to solve this long-

standing mystery,their findings

represented alandmark in theannals ofChesapeake Bay

science, but alandmark thatwas a long timecoming.Although scien-

tists first beganinvestigating the ori-

gins of MSX in 1958,the 20th century would

come to an end beforeBurreson and Stokes could eventuallypublish their findings. In the year 2000,they finally identified this deadly parasiteas a foreign invader.

Why did it take more than 40 years toanswer such a key question? Faced with aparasite of unknown origins, marine biol-ogists in the 1950s and 1960s foundthemselves working at the limits of theircurrent tool set, waiting for a break-through. In the history of science, whennew research tools come online, new dis-coveries soon follow — after new tele-scopes start up, new galaxies appear in thedepths of space; after deep submersiblesplunge to the sea floor, hydrothermalvents appear in the depths of the world’soceans.

For Burreson and Stokes and biolo-gists everywhere, the invention of a newtool called PCR — short for polymerasechain reaction — created a revolution intheir science in the early 1990s. Using thenew DNA-based tools of molecular biol-ogy, Burreson and Stokes were at last ableto trace the origins of the MSX epidemicto a parasite that invaded from elsewhere,probably as a hitchhiker on a non-nativeoyster.

If there are lessons to be learned fromthat long history, one of them might bethis: breakthroughs can breed hubris, whatphysicist Freeman Dyson called “a techni-cal arrogance that overcomes peoplewhen they see what they can do withtheir minds.” Innovations like PCR andnovel technologies for oyster aquacultureopen up discoveries and expand theoptions for commercial and ecologicalrestoration, reviving a dream in the oysterindustry of planting the Chesapeake withfaster-growing non-natives.

That dream focuses now on a Chineseoyster called Crassostrea ariakensis, but thevision has been around for 60 years,spurred by the commercial success ofJapanese oyster aquaculture in the PacificNorthwest. If it could be done elsewhere,the thinking goes, it could be tried herealso.

Humility, however, might be anotherlesson from history, humility in the face ofthe unknown and the untried.The devas-tation of MSX dates back 50 years now,and 40 of these years passed before scien-tists, thanks to a breakthrough, finallysolved the puzzle of its unknown origins.

Ironically enough, the scientistsresponsible for breakthroughs often see —more clearly than most — the limits oftheir knowledge. Some researchers warnthat we’ll never have enough knowledgeahead of time to predict accurately theoutcome of widespread introductions. Ifwe want to know the answer, we have torun the experiment.

The restoration of Chesapeake oysterswill be exactly that: a huge, system-wideexperiment in the country’s largestestuary.And the outcome is unknowable.

— Michael W. Fincham

Lessons of History: Hubris and HumilityT H E S T O R Y O F M S X

with names like Deep Water, Horsehead and Wreck Shoals. Reefslike these once made the James River the mother lode for newseed oysters for Chesapeake Bay.“It’s amazing,“ Burreson tells hiscrew,“they’ve got this reserve fleet anchored over what were oncethe most productive oyster grounds in the world.”

Closing with the fleet, Burreson and his crew find mothballedships lashed together side by side, with sharp, pointed bows tied tofat, round sterns.The U.S. Maritime Administration calls this col-lection the James River Reserve Fleet. Locals call it “the GhostFleet.” These rusting hulls carried men and women and weaponsto World War II, Korea, and Vietnam. Several ships made it to thefirst Gulf War. Now they float here, motionless, empty of peopleand cargo, their waterlines riding high above the river. Up top theycarry a jungle gym of smoke stacks and radar dishes and radio tow-ers with no signals to send. From the window of a control bridgesunlight flares out like a cannon flash from a long-forgotten battle.

COMING FAST ACROSS THE WATER HE CANsee the old fleet floating at permanent anchor. GeneBurreson is riding shotgun in a small runabout that isslicing straight across the James River, headed for the

world’s largest mothball fleet, an armada of decaying Navy shipsthat are clearly headed nowhere.

Tall, big-boned, and hatless, Burreson squints against thebright sun bouncing off the water. At 6’4” he towers over hisboat driver and three assistants crouching in the forward cockpitfor the bouncy ride across the river. From here the ships are adistant scraggle of grey hulks humped up against a brown-greenriver and distant, dark green trees.

Burreson is an oyster biologist with the Virginia Institute ofMarine Science (VIMS) and his target today is not the fleet butwhat lies beneath.Along the bottom of the river, sprawled underand around and south of the Navy ships are huge oyster reefs

4 • Chesapeake Quarterly

The MYSTERYThe MYSTERY

INVASION of Chesapeake Bay

INVASION of Chesapeake Bay

By Michael W. Fincham

Running close along the line of ships, Burreson starts to rousehis crew.“I’m worried about the Coast Guard coming out.Theyonly arrest the chief scientist,” he says.The low-key joke, deliveredin his bottom-key voice, seems to work. His lab assistants, threeyoung women in sunglasses, sunblock, and baseball caps, startpulling out dredging gear. It’s time to go to work.

There’s a long-standing mystery about the oyster reefs along theJames River.The mother lode is still there, but most of the oystershauled out of these waters never make it to market.When theseupriver oysters are replanted downriver they are supposed to growfat and salty. Now, however, they shrivel up and die, many of themvictims of a parasite called MSX.

Volume 5, Number 2 • 5

By Michael W. Fincham

The James River Reserve Fleet (shown above), often called the GhostFleet, dates back to 1925. By 1950, it held 800 ships, many of them reacti-vated for the Korean, Vietnam, and first Gulf wars. Like the oyster, the fleethas dwindled — only 57 now remain. PHOTOGRAPH BY MICHAEL W. FINCHAM.

Could a “ghost fleet” of crumbling

warships have anything to do with a

disease that has ravaged native oysters

for nearly half a century?

The dying started about 50 years ago.And it started suddenlyand massively over most of the southern Chesapeake.That’s onepart of the mystery.The dieoffs eventually spread north, reachingfrom the James River all the way up to the Bay Bridge.

And no one could figure out where this MSX parasite camefrom.That’s another part of the mystery.That’s one of the ques-tions that first brought Burreson out to these reefs.

But it would be years before he guessed how the Ghost Fleetcould be part of the answer.

IT BEGAN AS A PARTY ON DELAWARE BAY,a holiday picnic on one of the big commercial oyster boats,and two scientists — one at the beginning of his career, oneat the end — got to come along for the ride.The holiday

was Labor Day. The year was 1958.To celebrate the holiday, Norm Jeffries, an oyster grower out


of Port Norris, New Jersey, would load hisbest-looking boat with wife, family, andfriends and motor them out for a floatingparty and dress-up preview of this year’sharvest. It was a celebration of sorts, thisday on the water, an annual “trying of thegrounds” before the opening of the oysterseason.

Like farmers, oyster growers are gam-blers. Jeffries, the son of a Port Norrisoysterman, had borrowed heavily to plantoyster seed across hundreds of acres ofleased bottom. He brought scientists tothe party because he needed to knowwhether his bet had paid off.

The scientists on board often workedat the Rutgers shellfish laboratory atnearby Bivalve. One was Walt Canzonier,a young graduate student.The other wasThurlow Christian Nelson, a famous biol-ogist with a long list of honorary degreesand awards to his name, as well as morethan 125 publications, most of themabout Crassostrea virginica, the native oysterthat supported profitable fisheries inDelaware and Chesapeake bays.

Now 67, retired and ailing, Nelsontook a seat on a trunk cabin as the boatglided south past the grassy wetlands lin-ing the Maurice River and out onto thebroad flat reaches of the mainstemDelaware. From his perch on the cabin,Nelson could give orders and keep theyoung Canzonier busy.

The grad student’s job was to fill abushel basket with oysters, then empty itoyster by oyster, counting the living andthe dead. With oysters, the dead come intwo forms: boxes and gapers.When youcrack open an oyster and find it empty ofmeat, you call it a box.When you find theoyster hanging open with the meat deador decayed, you call it a gaper.

When the first oyster dredge hit thedeck, it was Canzonier who was down onhis hands and knees culling through oys-ters. Counting through the first bushel, hebegan calling out boxes and gapers at arate that stunned Nelson and every oneelse on board. Nearly all the oysters weredead.“That can’t be right,” Nelsonsnapped.“Count them again.”Young

Canzonier started over, counting out onedead oyster after another.

Perhaps this was just a bad patch, anodd local dieoff. Jeffries pulled his dredgeand motored away to try another oysterground.When he dumped the dredge ondeck, Canzonier sank to his knees againand again began calling out boxes andgapers. Jeffries headed for another oysterplanting.Then another.And another. Indisbelief, Nelson kept barking orders, call-ing for recounts.

Norm Jeffries just watched, shakinghis head, glancing at his wife.An oystergrower born into the business, he didn’tneed numbers to tell him they were in

When MSX invaded Delaware Bay, itbankrupted oyster growers and landedtheir boats on the beach. PHOTOGRAPH BY

MICHAEL HOGAN/HOGANPHOTO.COM.

The party was over for the

entire Delaware Bay oyster

industry. A devastating disease

was sweeping through oyster

beds all around the estuary.

deep trouble. Jeffries and his wife hadbuilt one of the most successful oysteroperations in the region, largely by float-ing huge loans, first to expand their plant-ings and later to build a shucking house.Planting oysters, he liked to say, was likeputting money in the bank.The moremoney he put in the bank, the larger theloan he could take out.There was a catch,of course. He had to pay all those deck-hands, all those shuckers, all those loans.He had to harvest a lot of oysters.

Finally he steamed across to the east-ern side of Delaware Bay, to his prizedCape Shore grounds where he had madehis largest, most expensive planting yet.The Cape Shore grounds had paid offwell in the past — but not this year.Thedredge came splashing up, Canzonierdropped to his knees, and Jeffries discov-ered there would be no money going inthe bank this year.The dying was generalall over Delaware Bay.

The party was over — not just forJeffries, but for the entire Delaware Bayoyster industry. A devastating disease wassweeping through oyster beds all aroundthe estuary.Within two years thecommercial harvests were cut by over90 percent.

Norman Jeffries, the 61-year oldoyster grower, lost everything.“He wentinto bankruptcy,“ says Canzonier. He soldoff the business, then the shucking house,then the boats.“The creditors took every-thing he owned — except for one littleboat that was listed in his wife’s name,”says Canzonier.All along the north shoreof Delaware Bay, in little towns likeBivalve and Shellpile and Port Norris,local growers and watermen by thedozens lost their boats to the banks andwent out of business.

Chesapeake Bay was next.A year laterthe same disease swept through the lowerBay, killing millions of oysters in MobjackBay and in the lower reaches of the Yorkand the James and the mainstem estuary.Within three years oyster harvests inVirginia dropped by 75 percent andoyster growers were getting out of thebusiness.

Out on his holiday boat ride Walt

Canzonier had become an accidental wit-ness to a turning point in ecological his-tory. As he knelt on deck counting allthose boxes and gapers he was document-ing, unknowingly, the first, sudden sign ofan oncoming ecosystem decline.

These oyster dieoffs would do morethan put a lot of oystermen out of businessin Delaware, Maryland, and Virginia: theywould change the ecology of ChesapeakeBay.

THURLOW NELSON WASseeing jello-like blobs, dozens ofthem, each one stuffed with dark,round dots.

Sitting at his microscope, he wassquinting at oyster tissue riddled withsome kind of unnamed parasite.The blobs,roundish and irregular, seemed to be sin-gle-cell plasmodia, and the dots seemed tobe nuclei, but Nelson could not identifythe mystery killer, and neither couldHarold Haskin, his protégé and now thedirector of the New Jersey oysterlaboratories.

The mystery only deepened whenthey called in other experts. Leslie Stauberfrom Rutgers was a leading authority onparasites, and John Mackin from TexasA&M had looked at more oyster slidesthan anyone else in the world. Both poredover the new slides and paged through theresearch literature, pulling out photographsand drawings, hunting for a match. Bothsearched their memories, and in the endboth made the same report: they hadnever seen this organism before.

What they could see was the route ofinfection.The parasites invade through thegills, sucked in as the oyster feeds. Once inthe gills, they divide and multiply rapidly,eventually breaking through to the circula-tory system and moving easily throughoutthe body.With its tissues overwhelmed andits nutrients absorbed by the parasite, theoyster soon shrinks and dies.

Even Walt Canzonier, the grad student,got his turn at the scope.“The plasmod-ium was spherical, and it was full ofnuclei,” says Canzonier.“We were sittingaround looking at this parasite.And wedidn’t know what it was.”

Since the new parasite needed a name,lab director Haskin gave it one.“Well, it’sobvious,” he told the scientists gatheredaround the microscope.

“This is multi-nucleated sphere X. OrMSX.” The X stood for origin unknown,and the name stuck because the mysterystuck.

Gene Burreson swings a small oysterdredge over the side of the research boatand splashes it down towards the bottomof the James River.The research boatguns forward, the line starts vibrating, andthe dredge digs into the unseen oysterreef below.

The biologist and his crew are nowworking the Horsehead oyster groundsjust downstream from the Ghost Fleet.Scientists like Burreson have been comingback to these James River reefs every yearfor nearly half a century now, hoping tofind evidence the dying is over.

Burreson is one of a second generationof oyster scientists to tackle the mysteriesof MSX, and his assistants will be part of athird generation. Early researchers at theRutgers shellfish laboratories were able toclassify the parasite as Haplosporidium nel-soni, a protozoan with at least two life his-tory stages: spores and plasmodia. Over thedecades they would document how warmwinters, drought years, and high salinitieshelped spread MSX and how cold win-ters, rainy years, and low salinities helpedslow it down. By selecting and breedingMSX survivors, scientists even made goodprogress in developing disease-tolerantoysters in the lab.

Certain tough questions, however,remain unanswered, passed down toBurreson’s generation.What are theother life stages and where are they?Scientists think there is more to MSXthan spores and plasmodia, the two lifestages they can see in oysters.Thoseother life stages probably occur in anotherorganism, an alternate host that carriesMSX around and releases it where it caninfect oysters. Could it be carried bycopepods floating in the plankton, wormsin the sediment, even fish or crabs?There are dozens of possibilities and no


answers to the question (see The MissingLink, p. 14).

While researchers have wrestled withthese questions over the last half century,MSX has been depopulating the oystergrounds of Chesapeake Bay, especially dur-ing drought years. In the last decade and ahalf, a second disease called Dermo —

caused by another protozoan parasite,Perkinsus marinus — also exploded throughthe Bay’s dwindling oyster populations (seeThe Culture of Disease, below).TheChesapeake lost bottom reefs, a majorhabitat for biodiversity, as well as millionsof filter-feeding oysters, a major force forwater clarity. By the early 21st century, 99

percent of the oysters were gone andthe ecology of the Bay had changeddramatically.

As the small dredge rises, dripping, outof the river, Burreson and a young, red-haired lab assistant swing it on board anddump its contents. Like rocks hitting aboardwalk, dozens of oysters thud acrossthe culling board. Burreson and his crewtug on gloves and start digging throughthe pile with knives and hammers.

Cracking apart a clump of oysters,Burreson holds open two interior shells,each covered with a brown, scum-likebiofilm. He points to several barnaclesgrowing inside the shell.“This is an oysterthat’s probably been dead for six months,”he says, flipping it overboard.“Maybe ayear or more.”

He taps an oyster with his knife.“Itlooks perfectly healthy,” he says, but thehollow-sounding knock tells him other-wise. Cranking it open, he finds no meatand no biofilm, just two shiny, pearl-whiteshells,“which means this is a real recentmortality, probably within the last week orso. It’s an indication that there is a mortal-


The Culture of Disease

Thurlow C. Nelson (left) was the famous son of a famous scientist, Julius Nelson, who pioneeredthe study of oysters in New Jersey. The son extended his father’s work, with new findings thatproved crucial to the oyster growers of Delaware Bay and led to the creation of two shellfish labo-ratories. Harold Haskin (right), a protégé of Thurlow Nelson, gave the MSX parasite its popularname and organized long-term studies on the biology and ecology of the organism.

Dermo, not MSX, is now the dominantoyster killer in Chesapeake Bay. A pro-tozoan parasite, Dermo (known to sci-

entists as Perkinsus marinus) was first docu-mented at low levels in the Bay in 1949, adecade before MSX showed up. It may havebeen here forever, scientists say, or it may havebeen carried in from southern U.S. waterswhere it had been killing oysters for years.

In the mid-1980s, a series of warm wintersand dry summers unleashed a Dermo epi-demic in Chesapeake Bay, and by 1990,Dermo had exploded in Delaware Bay also.A remnant population left over in low levelsfrom the 1950s had apparently endured, mov-ing from oyster to oyster and surviving coldwinters in small numbers, suggests Susan Ford,a researcher at Rutgers University’s HaskinShellfish Laboratory in Bivalve, New Jersey.In Delaware Bay, Dermo has so displaced MSXas Parasite Enemy Number One, that in Ford’swords, “If we didn’t have Dermo we wouldn’thave a disease problem.”

In Virginia,VIMS researcher Gene Burresonnotes that when Dermo moved into the richseed areas of the James River it brought theoyster industry to its knees. Back in the 1950s,

he says, some 75 percent of theharvest came from leased bottomstocked with James River seedoysters — 3 to 4 million bushels ayear. First MSX arrived, then afterthe 1980s drought, Dermo fol-lowed saltier water up into therich seedbeds and hit the oysters— and the oystermen — hard.

“They just lost everything,” hesays.

What have we learned aboutthis other oyster killer? How doesit survive? How does it grow?Does it have an Achilles Heel?

To attack these questions, sci-entists sought to study the para-site under controlled conditions inthe laboratory, but as the 1980sgave way to the 1990s, they didnot yet know how to cultureDermo and had to rely on sam-ples gathered from the wild.

Culturing an organism in thelaboratory is a key step in biologi-cal research. Cultures providecontrolled populations for ongoingstudies of all kinds. But coaxing amicroorganism to grow outside of

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Dermo arrived early in the Chesapeake, but its effectin Maryland wasn’t fully felt until years after MSX hit, whendrought caused both diseases, which thrive in higher salinities,to spread.Together, these diseases decimated what was oncethe Chesapeake’s most valuable fishery. SOURCES: GRAPH, NOAAFISHERIES ANNUAL COMMERCIAL LANDINGS STATISTICS DATABASE.ZOOSPORE DRAWING, THE EASTERN OYSTER: CRASSOSTREAVIRGINICA, BY KENNEDY, NEWELL, AND EBLE.

Dermo, biflagellated zoospore stage

ity going on up here at Horsehead,” hesays.“The salinity is just high enough thatit could be from MSX.” Dead oysters havea tale to tell, and the moral of this tale isno surprise: after nearly 50 years MSX isstill killing oysters in Chesapeake Bay.

As Burreson scrabbles through his pilesof oysters, he keeps looking for live adults.Gapers and boxes and small oysters goback overboard, but his keepers go into asmall bucket for the boat ride back to thelab.Adults usually carry heavy loads ofparasites, and Burreson has been pioneer-ing a technique for analyzing the MSXsamples, a technique never dreamt of backin 1957 when MSX first showed up.

Live oysters, it turns out, also havesome tales to tell — and one of the talescomes with a surprise ending, an answerto the enduring mystery: where did thiskiller parasite come from?

BURRESON’S FIRST CLUEScame from scientists studying oys-ters from Korea and Japan. In1971 Fred Kern was analyzing

oysters at the Bureau of Commercial

Fisheries laboratory in Oxford, Marylandwhen he saw parasites in Korean oystersthat looked like MSX.The clue was asimilarity based on a shape, a shape seenthrough a microscope, something akin toa witness watching a police lineup full ofsuspects who are all about the same size— but are all wearing masks.

In 1991, Carolyn Friedman had thesame reaction while she was checkingJapanese oysters with the CaliforniaDepartment of Fish and Game. In bothcases the MSX-like parasite turned up inCrassostrea gigas, a fast-growing Japaneseoyster that has been profitably grownsince the 1930s in California, Oregon, andWashington State. By the mid 1990s, the

question of MSX’s origins had been inthe cold case files for nearly four decades.Scientists had clues, but no way to followup, no way to unmask any suspects.

A breakthrough was coming, however,and it began late at night in 1983 on alonely road in the hills of northernCalifornia. Kary Mullis, a lab technicianwho dreamed of being a novelist, wasdriving to his cabin in the woods, mullingover ways to analyze mutations in DNAwhen — in a flash of insight — he saw anew way of making copies of DNA.Ashe drove he became so excited, he laterwrote, that he woke up his girlfriend totell her. He also began dreaming about aNobel Prize.

His insight led eventually to an inven-tive technique called PCR, short forpolymerase chain reaction, a techniquethat allows scientists to multiply one smallpiece of DNA into millions of pieces.PCR became the hottest tool in molecu-lar biology, opening the door to all kindsof new experiments and applications andinvestigations. Doctors could use PCR fordiagnosing diseases, chemists for creating


It took a technique never

dreamt of back in the 1950s,

when MSX first showed up,

to solve the mystery of the

parasite’s origin.

its native habitat can be tricky —after a half-century of research,

researchers still cannot culture theelusive parasite MSX.The effort to develop a reliable

method for culturing Dermo became pri-ority number one for researchers like

Gerardo Vasta at the University of Maryland’sCenter of Marine Biotechnology (COMB) inBaltimore.

Vasta was well equipped for the task. Hehad two Ph.D.’s — one in biochemistry andone in zoology, both from his home country ofArgentina.Vasta had come to the U.S. in 1979on an international scholarship, and he soondiscovered that oysters and their immune sys-tems provided excellent biochemical models.

In 1989, only four years after the creationof COMB,Vasta joined the new faculty. Rightaway he focused on the oyster’s defensemechanisms, especially its defenses againstDermo.The lack of a reliable means to cultureDermo in the laboratory proved afundamental barrier in pursuingthis research, and so he set hissights on that.

Vasta and his colleague JulieGauthier proceeded to testone growth medium after

another,Vasta drawing on his extensive knowl-edge of mammalian systems and applying it tothis marine organism. During 1992 and 1993,their breakthrough came, and they announcedtheir development of a novel means for cultur-ing this parasite that was ravaging the Chesa-peake’s oyster bars.

It was a spectacular moment for oysterresearch.With federal funds and scientific com-petitiveness at a peak, other researchers alsodevised methods for culturing Dermo at aboutthe same time. Jerome La Peyre at VIMS andStephen J. Kleinschuster at the Haskin ShellfishLaboratory at Rutgers University used differentmethods, but all three teams soon reportedtheir findings in the scientific literature.

The breakthroughs did not stop there.Vasta’s lab went on to produce molecularprobes for Dermo, with work done by AdamMarsh, who later joined the faculty at the Uni-versity of Delaware. Now, within a matter ofmonths,Vasta says that his lab, working withthe Institute for Genomic Research (TIGR), willcomplete the sequencing of Dermo’s entiregenome.

According to Kennedy Paynter,a longtime oyster researcher atthe University of Maryland Col-lege Park and the UM Center

for Environmental Science, the ability to cultureDermo has allowed researchers to ask andanswer important questions, to test the para-site’s response to salinity and temperatureranges. “We can see which conditions spur theparasite’s growth and which hinder it,” he says.

The molecular probe has also allowed sci-entists and research managers to pinpoint thepresence of Dermo, whether in an oyster or inthe environment.

Surveys conducted by Vasta and his col-leagues from New England to the Chesapeaketurned up Dermo everywhere. It used to bethat oysters from Maine were uninfected, hesays, but in a recent batch of Maine oystersVasta found that 30 percent were infectedwith the disease.

The future will not be easy for oysters fac-ing this persistent parasite, but Vasta remainsoptimistic. He envisions finding Dermo’s weakspots — in its need for iron to fuel its metab-olism, for example — and using selectivebreeding or genetic manipulation to tilt thistough biological battle in favor of the nativeoyster.

— Jack Greer andMichael W. Fincham

new drugs, police for doing DNA finger-printing. It was a dream come true forbiologists — and for Kary Mullis: in1993, at age 49, he won his Nobel Prize.

For Burreson, the biologist-turned-detective, it was the dream tool for crack-ing the long-standing mystery of MSX.His first step was to hire Nancy Stokes, ascientist trained not in marine science butin the new DNA-based tools of molecu-lar biology.With the PCR technique theycould finally do more than peer at para-sites through a microscope: they could tryunmasking them by examining theirDNA.

Their approach was elegant in con-cept: compare the DNA of theChesapeake parasite against the DNAof the Japanese parasite.Was the killer inthe Chesapeake a parasite from Japan?

Sitting down at his high, black lab bench,Burreson picks up an unshucked oysterand inserts a long, thin needle through theshell, slowly plunging it into the adductormuscle. Much like a doctor during anoffice visit, he’s taking a blood samplefrom a sick oyster, one of his James Riveroysters infected with MSX.The oyster, aperfect patient, doesn’t flinch.The bloodcomes up the needle as a clear liquid.

This is the first step in getting a pureDNA sample of MSX. Floating in thecolorless blood are blob-like plasmodia.When Burreson squirts his blood sampleinto a petri dish holding a saline solution,the plasmodia continue to float while theblood cells settle out and stick to the glass.He pours his solution into another dish,and the blood cells settle out again. Bypouring and settling several times, hegradually discards most of the oyster cellsand concentrates the MSX cells.“Thatwas the hardest part,” says Burreson,“get-ting the pure MSX DNA without a lot ofoyster DNA contaminating it.”

The rest was hardly easy.With thesesamples Burreson and Stokes first had tocreate a DNA fingerprint for MSX.AndPCR was their key tool because it gavethem a lot of DNA to work with.

Using cycles of heating and coolingplus a key enzyme, PCR can split a DNA

strand in two and then create two separatecopies. By running the process multipletimes — the heating, the cooling, theenzymes — scientists are, in effect, settingoff a chain reaction.They are copying thecopies, then copying the copies of thecopies until they have quickly “amplified”one piece of MSX DNA into millions ofpieces.

With all those DNA copies, Burresonand Stokes went looking for some of thesignature genes that define MSX as MSX.After picking one sector of one key gene,they were able to outline a 564 base pairsequence that was unique to the parasite,as unique as a fingerprint to a criminal.

Their work, for the first time,unmasked MSX, the Chesapeake oysterkiller. It identified the parasite not by itsbody shape as seen under a microscope,but by a diagram of its underlying DNA,its genetic fingerprint.

Like any detective worth his badge, thebiologist took his new tools and startedrounding up the usual suspects and finger-printing them.

In this case the suspects were Japaneseoysters that came from the far side of thecountry and the other side of the world.Burreson gathered tissue slides or spat orliving oysters that originated in Matu-shima Bay in Japan, in Geoje Bay inKorea, and in Drakes Estero in MarinCounty, California.

Thanks to his work with PCR,Burreson now had a molecular probe thatwould seek out and stick itself to anyDNA from MSX in any samples of oystertissue.When his probe turned up MSX inthe tissue of all his non-native suspects,the last mask was lifted: MSX, the killerparasite, was carried in oysters from Japan,Korea, and California.

For a final proof, Burreson andStokes sequenced a section of DNAfrom the parasite in Japanese oysters.When they compared it with theirearlier DNA fingerprint from theChesapeake parasite, they found anear-perfect match, a 99.8 percentmatch that would convict a culprit inany court.“That is conclusive evidencethat the parasite in Crassostrea gigas is, in


Blobs full of nuclei (right) are whatresearchers see today — just as they did 50years ago — when they look at MSX under themicroscope. To finally unravel the mystery ofthose blobs, Gene Burreson and Nancy Stokes(above and opposite page) used new technolo-gies in the 1990s to show the organism’s DNAsequence on X-ray film (opposite page). Todaythey use laser scans and computer programs toread its DNA sequence digitally (above).

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fact, MSX,” says Burreson.“They are thesame organism.”

His final verdict: the Japanese oysterwas the culprit. It sometimes carriedMSX, a parasite that seldom sickened gigasbut was lethal to oysters in both Delawareand Chesapeake bays.“MSX was likesmallpox coming in with the Europeans,“says Burreson,“and the native Americanswere wiped out, because they were naïveto it.They hadn’t seen it.”

An answer like this only leads, ofcourse, to a new question: who broughtJapanese oysters — and MSX — into theChesapeake?

T HE FIRST PERSON TOplant Japanese oysters in EastCoast waters was probably a sci-entist. Sometime in the early

1930s, a researcher drove down to theNew Jersey shore, carrying a bushel ofJapanese oysters and planted them inBarnegat Bay, a narrow estuary behind thestate’s barrier islands.The scientist wasnone other than Thurlow C. Nelson,already chairman of the Zoology

Department at Rutgers and director ofNew Jersey’s two shellfish laboratories.

His Japanese oysters grew quickly atfirst, raising his hopes that gigas oystersmight revive Barnegat Bay’s strugglingoyster industry.After two weeks, the oys-ters stopped growing and gradually diedout, perhaps from low salinity and lowoxygen. But Nelson’s interest was piqued.If he wasn’t the first person to ever plantCrassostrea gigas in East Coast waters, hewas certainly the first to talk about it.

In the spring of 1946, shortly after theend of World War II, Nelson strode to thepodium at the New Yorker Hotel and toldthe annual convention of the NationalShellfisheries Association that it was timeto try planting oysters from Japan in EastCoast waters like Chesapeake andDelaware bays.

It was a powerful message to animportant audience. Nelson was a well-established scientist, and his audience thatday included members of the OysterGrowers and Dealers Association of NorthAmerica. In the decade before World WarII, growers along the West Coast had donevery well importing, planting, and harvest-ing a Japanese oyster called Crassostrea gigas— so well that East Coast growers beganworrying about losing the post-war mar-

ket to the faster-growing Japanese oyster.World War II was now over, seed oystersfrom Japan were becoming available again,and a post-war economic boom seemedto be gearing up.

It was a propitious moment for opti-mism and Nelson was nothing if not opti-mistic about the potential of the Japaneseoyster. He extolled its fast growth in high-salinity waters and passed along reports offour-foot oysters once found in Japan.“If itwere possible to obtain in our Eastern oys-ter the rapid growth of the Japanese oys-ter,” he argued,“it would revolutionize ourindustry.” He called for Japanese oysters tobe “promptly shipped” to shellfish labora-tories on the East Coast. To an audience ofoyster growers he also suggested that “testplantings be made on a small commercialscale under natural conditions.”

GENE BURRESON FOUNDa copy of Nelson’s 1946 speechwhen he was sleuthing throughthe historical literature, looking

for evidence of early introductions ofJapanese oysters. From historical recordslike this he arrived at an uncomfortablescenario: scientists like Nelson and grow-ers like those in his audience may havebrought in MSX.


Gene Burreson draws a blood sample from asick oyster, the first step toward creating aDNA fingerprint of the MSX parasite.

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At first only a few people followedNelson’s advice about testing Japaneseoysters, at least according to the publishedreports that Burreson found. In 1949 ashellfish manager on Cape Cod plantedsix bushels of spat into BarnstableHarbor.That same year wildlife officialsin Maine tried a small planting ofJapanese and European oysters in a pond,and Victor Loosanoff, director of a federalmarine laboratory, planted Europeanoysters in the waters of Maine and Con-necticut.According to a 1950 report,there were also “numerous attempts” atintroducing Japanese oysters in LongIsland Sound.

In Nelson’s speech, in hindsight, aresome of history’s terrible ironies — andperhaps some scientific hubris.The sirencall of fatter, faster-growing oysters appar-ently led some scientists and growers totry planting local waters with non-nativeoysters — and all their hidden hitchhik-ers. In popularizing the potential ofJapanese oysters, Nelson may have unwit-tingly helped call down the destructionof the native oyster species he spent hislife studying.

For Burreson, the reports and theanecdotes are evidence of a trend, areadiness on the part of scientists andgrowers along the East Coast to experi-ment in a casual fashion with Japaneseoysters.“It was brought in a lot by scien-tists,” says Burreson.“They would bringthem in and just put them off the dockor put them in trays to see how theywould grow. It was done by industrymembers [oyster growers] as well,probably a lot, but not nearly so welldocumented.”

It’s not surprising that Burreson’sclaims have stirred some dissent, especially

from scientists who worked at Nelson’sold lab at Bivalve, New Jersey.“Somepeople would like to say Doc Nelsonbrought gigas into Delaware Bay.” says WaltCanzonier, the former grad student whoworked with Nelson nearly 50 years ago.“I don’t see anything in the record toindicate that. He may have had gigas hereto work with, but not in very large num-bers, that’s for sure.”

Despite his claims for Japanese oysters,Nelson had little reason and probably nofunding for launching a major researcheffort or planting program in DelawareBay, says Susan Ford, another scientistwith the Rutgers Bivalve Lab.“In theearly 50s, oysters were not in short sup-ply,” argues Ford,“so there would nothave been any emphasis to do anythingserious.” Growers elsewhere along thecoast may have been planting gigas, as thehistorical records suggest, but there is noevidence, says Ford, that anybody testedgigas in Delaware or Chesapeake bay —at least in the years before MSXappeared.

After MSX struck, everythingchanged. New test plantings, most ofthem small scale, were reported inDelaware, Maine, Massachusetts, Mary-land, and Virginia.And always there wereanecdotes of unreported plantings. One ofBurreson’s favorites is the story of theman who brought Japanese oysters homefrom the Seattle World’s Fair of 1962 andplanted them off his dock.An ambitiousseafood entrepreneur admitted plantinggigas in Maryland waters in the 1970s, anda Virginia grower announced at a scienceconference that he made large plantingsduring the 1980s.

By the 1990s, the Virginia SeafoodCouncil, in hopes of saving a decliningseafood industry, was asking scientists tofind an alternative oyster to replace therapidly disappearing native oyster.The firststrong candidate that scientists put for-ward for planting in the Chesapeake was,ironically enough, the Japanese oyster,Crassostrea gigas.And one of the scientistswho went to work researching the poten-tial for gigas in Chesapeake waters was,ironically enough, Gene Burreson.

T HERE’S A SECOND UNSET-tling scenario for the MSXinvasion.llllIn 1946 when Nelson was call-

ing for the planting of Japanese oysters,the old Ghost Fleet of mothballed Navyships was bringing more ships into theJames River every week.With the end ofWorld War II, hundreds of ships werearriving in Chesapeake Bay and steamingupriver for long-term anchorage.Theywere sailing back from Europe — andfrom Japan.

In 1950, the James River ReserveFleet hit its historic high with 800 shipslashed together in groups of 12 to 30ships, a flotilla that stretched miles up theriver. Between 1950 and 1954, many ofthose ships were reactivated to carrytroops off to the Korean War — andbring them home again. By 1957 MSXbegan showing up in oysters.

The timing of all that shipping trafficand the sudden onslaught of MSX a fewyears later is, at the least, suggestive. Shipscan carry MSX in various ways. Oysterscan attach to their hulls, says Ford, andMSX and perhaps an alternative hostcould be hitchhiking here in ballast water.If ships dump their ballast water or theirbilge water in the Bay, they could bereleasing those MSX or its hosts intothe Bay.

“Let’s look at this scenario,” saysCanzonier who finds this option moreplausible.“Suppose we had MSX in theChesapeake Bay for a number of yearsbeing introduced by the Naval fleet com-ing from Korea.And it just never flaredup because conditions were not quiteright.” MSX may have invaded theChesapeake first and then shipped northto Delaware with James River seed oys-ters, says Canzonier, now president of theNew Jersey Aquaculture Association.

“Perhaps in the mid-1950s, the envi-ronmental conditions were more appropriate in Delaware Bay or the alter-nate host was present in sufficient number,”he says Canzonier.“And it caught fire herebefore it caught fire in Chesapeake Bay.”


If one exotic oyster species

brought disease, can we

depend on another species

of non-native oyster to

restore the Chesapeake?


Measures to control malaria improvednearly overnight after the 1897 discov-ery that mosquitoes play a role in the

life cycle of the malaria parasite, Plasmodiumspp. This ancient disease, according to recentresearch, probably played a part in the down-fall of the Roman Empire in the 5th centuryand nearly stopped the building of the PanamaCanal in the 20th century.When simple pestcontrol measures were put in place aroundthe Panama Canal dig, the number of deathsfrom malaria dropped nearly eight-fold in thespan of just three years. Even in the 21st cen-tury, reducing mosquito abundance remains areliable control strategy for harnessing thespread of this global disease.

What if the mosquito’s role as intermediatehost in the life cycle of the malaria parasitehad remained stubbornly hidden? It’s hard toguess at the impact. But the prolonged mys-tery of the missing host for the MSX parasitehas no doubt hastened the decline and fall ofthe oyster empire of the Chesapeake Bay.

Since the 1960s, generations of scientistsstudying MSX have searched for answers tothe transmission question.They’ve found thatnative oysters never “catch” an MSX infectionin the lab from infected oysters placed next tothem. But when scientists place healthy oystersin a Bay area empty of oysters, the clean oys-ters “catch” a heavy MSX infection –– andvery quickly. Since other oysters apparently donot release infective particles, some other ani-mal — the alternate host — must be releasingMSX.

What is this alternate host? A crab, a cope-pod, a worm? In 2006, scientists still don’t havethe answer –– but not for lack of trying.Every two weeks, over a three-year periodthat started in 1999, scientists sampled anarray of organisms for MSX, using both con-ventional and molecular techniques. “We sam-pled literally every organism we could get ourhands on,” says VIMS oyster biologist GeneBurreson. “As you can imagine, the number ofpossible organisms is huge,” says Rutgers biolo-gist Susan Ford, who worked with Burresonon this study.

Burreson and Ford no longer have targetedfunding to pursue the search for MSX’s alter-nate host but they haven’t given up.They arestill sampling. “We hope we are going to getlucky,” Burreson says.

Burreson feels strongly that MSX’s alternatehost must be something that eats the sporesthat form as one stage of the parasite’s lifecycle. But the spores are tiny, just 7 microns,

and almost any-thing could eatthem.“If we hadnarrowed it downand could say,‘look, it’s in worms,’that’s one thing,but we can’t sayanything still,” hesays.

Part of theproblem, explainsmathematical biol-ogist MarjorieWonham, is thatdisease cycles inmarine systems ingeneral are muchless well-knownthan those in ter-restrial systems.“When you areliving in the water,you are in a soupof organisms thatrange from thenano to micro-scales.There are alot more optionsavailable as potential intermediate hosts.”

And water is so much harder to search,Wonham continues. “We don’t live in theocean.We don’t have the same ease of accessand intuition about marine systems as we havewith terrestrial systems,” she says.Wonham,who works at the Center for MathematicalBiology at the University of Alberta in Edmon-ton, Canada develops models to predict out-breaks of West Nile Virus and invasive speciesintroductions through ballast water exchangein the Great Lakes.

Until they unveil MSX’s intermediate host,scientists will lack the ability to control thetransmission of MSX. Generally speaking, “ifyou don’t understand the life cycle [of a para-site], you have no hope,” says ecologistAndrew Dobson of Princeton University, whostudies the role that parasites play in the pop-ulation ecology of infectious disease.

In the case of malaria, Dobson explains,once British medical officer Ronald Ross dis-covered that mosquitoes enter into the para-site’s life cycle twice, once to transmit the dis-ease to humans and once to receive the para-site back from human hosts, he rapidly con-cluded that controlling mosquito abundancewould be key. “Targeting the right point of the

parasite’s life cycle gives you a lot of insight,”Dobson says.

But in the case of MSX, just knowing thealternate host likely would not be enough. “Itmight help,” says Ford, “but how would youcontrol copepods or worms? Remember, wedo know how Perkinsus marinus [Dermo] istransmitted and it continues to kill oysters inlarge numbers.”

The unknown intermediate for MSX alsoclouds the question of the parasite’s introduc-tion to Chesapeake Bay. It is possible that MSXcame to the Chesapeake, not with Japaneseoyster (Crassostrea gigas), but inside this hypo-thetical intermediate host by some yetuncharted route.

Solving the mystery of MSX’s middlemanwould open new doors in understanding thedisease. But detectives Burreson and Ford maybe up against a funding roadblock in continu-ing their search. “You have to sample a lot oforganisms and that’s been the problem. It’srisky research for people willing to give youmoney,” says Burreson. “If you do solve it, thenI think the payoff is certainly worth it.”

— Erica Goldman, with reporting by Michael W. Fincham

The Missing LinkMSX Middleman Remains Elusive

A lingering mystery, the suspected alternate host for MSX remains unknown toscientists despite years of dedicated effort. Knowledge of the parasite’s complete lifehistory could provide clues for controlling the spread of the disease. DRAWINGS ADAPTEDFROM THE EASTERN OYSTER: CRASSOSTREA VIRGINICA BY KENNEDY, NEWELL,AND EBLE.

MSX Life Cycle

oystergills

sporestage

plasmodiumstage

unknownhost

Working just south of the GhostFleet, Burreson and his crew finishculling through their last dredge load ofJames River oysters.The biologist leansover and peers at his one bucket of liveoysters, then with a sweep of his armshoves all the shells and dead oystersoverboard.

“It’s possible that MSX came inballast water,” says Burreson, glancing atthe ships to his north.“Some of theseships here were probably involved inmoving troops from Korea. It could havehappened during that period.And thereare some cases where ships came fromKorea into Delaware Bay and dumpedballast water there.”

Naval ships, of course, were only partof the shipping traffic that was steamingthrough the Chesapeake and Delawareduring the 1950s carrying cargo andballast water and perhaps MSX fromKorea and Japan.As the size and speedof commercial tankers and freightershave increased in recent years, ballastwater has emerged as a major researchfocus for invasion ecologists, whosuspect numerous organisms areoffloading in our coastal waters.Theballast water research team at theSmithsonian Estuarine Research Centerestimates more than 150 invasive speciesare now surviving in the Chesapeake.The Chinese mitten crab may be thelatest arrival.

W HO STARTED THEMSX invasion of theChesapeake?11The interim verdict: the

MSX invasion may have begun with anexperiment by an oyster scientist, with aplanting by a grower, with a ballast waterrelease by a ship — or with all of theabove in several places on several dates.The jury is still out, the history still opento debate. “We can’t pin it down to a par-ticular introduction in a particular place,”says Burreson,“but we are convinced ithappened with that oyster [gigas].”

The future is also open to debate.Withnative oysters now depleted, thanks in partto a Japanese oyster parasite, some scientistsand growers and politicians want torebuild the commercial seafood industryand perhaps restore the Bay’s ecology byplanting Chinese oysters, Crassostrea ariak-ensis, in the Chesapeake. It’s a prospect thatstirs considerable debate in the scientificcommunity, yet a prospect that Burreson,surprisingly enough, does not oppose.

There may be lessons in his research,but keeping out ariakensis is not one ofthem, at least for Burreson.“People arenow using this [finding] as an argumentagainst introducing ariakensis,” saysBurreson before offering a different, moreupbeat reading of his own research.“Itshows what can go wrong,” he says,“when you don’t do things right.”

Contemporary scientists, in his opin-

ion, are doing things right: they are keep-ing ariakensis oysters isolated in hatcheries,then spawning sterile offspring, and onlythen trying test plantings in the Bay. Ifthis approach had been followed withJapanese oysters, he says, MSX wouldnever have invaded these waters.

Burreson, like Thurlow Nelson 50years ago, is optimistic that science mayyet find or build a better oyster for theBay.Through patient crossbreeding,researchers at Rutgers and VIMS havedeveloped several strains of disease-resist-ant native oysters for use by the aquacul-ture industry.And Mother Nature all byherself, through natural selection, maybuild a native, disease-tolerant oyster forthe Bay. Oysters that survive MSX tend topass on their resistance to their offspringuntil, over the long generations, an MSX-tolerant oyster emerges.That process hasalready worked in Delaware Bay, accord-ing to Susan Ford, and it may one daywork in the Chesapeake.

Some mysteries remain — and someironies. Burreson’s work with MSX con-tinues because, even after half a century,key questions about the disease have neverbeen solved.The other life stages of MSXremain unknown, as does the alternatehost. Burreson and his team keep search-ing for the DNA of MSX in dozens ofspecies, hoping to find the host specieswhich carries MSX around the Bay.“It’slike searching for a needle in a haystack,”he says.“I hope somebody cracks thisbefore I die.”

Thurlow Nelson, the man with highhopes for Japanese oysters, died longbefore any MSX mysteries were solved.On September 12, 1960, he left his sum-mer cottage near Cape May as HurricaneDonna swept up the coast. Hoping to tieup his rowboat, he waded out intoDelaware Bay and drowned there in therough waters of the rising storm.

The biologists he mentored decided tohonor his memory in the name of a newspecies they called Minchinia nelsoni —and, later, Haplosporidium nelsoni — thescientific term for the parasite Nelsonknew only as MSX.— E-mail the author at [email protected]


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“We can’tpin it down

to a particularintroduction...

but we areconvinced

it happenedwith that

oyster[gigas].”

Underwater grasses, orsubmerged aquaticvegetation (SAV), play

a key role in the ecology ofcoastal waters, and especiallyin Chesapeake Bay — thenation’s largest estuary.Thesegrasses provide habitat for bluecrabs and fish, and food forwaterfowl.They help keepwaters clear and offer shelterand living space for manyaquatic species.

Over the past several decades, cloudedwaters — a result of too many nutrientsand too much sediment — have blockedsunlight and smothered many SAV beds.Efforts are currently underway to helpmap, study, and reestablish underwatergrasses in the Chesapeake and othercoastal waters.

To help citizen volunteers, students,and others interested in learning moreabout these plants, Maryland Sea Granthas produced a new guide to underwatergrasses in collaboration with the National

Oceanic and Atmospheric Administra-tion’s Chesapeake Bay Office, the Alliancefor the Chesapeake Bay, and the MarylandDepartment of Natural Resources.

This 80-page guide, Underwater Grassesin Chesapeake Bay & Mid-Atlantic CoastalWaters, is 8.5” wide and 5.5” tall and fea-tures more than 100 color photographs,55 line drawings and helpful descriptionsof 20 of the most common SAV species,along with other aquatic species youmight see. The spiral-bound book isprinted on heavy, waterproof stock, similarto the marine mammal guides published

by Alaska Sea Grant and Rhode IslandSea Grant.The guide also includes waysto distinguish between similar plants, aswell as additional information about float-ing aquatic vegetation and algae, includingalgal blooms that can impact water qual-ity. Charts and maps detail the salinityrange of each SAV species, includingexpected salinity ranges in ChesapeakeBay during wet and dry years. Especiallyuseful is an identification key with detailsabout leaves, stems, and other characteris-tics to help the user identify the plant inhand.

The guide costs $29.95 plus $2.00shipping and $1.50 tax (Maryland resi-dents only). To place an order and pay bycheck,visit the web at www.mdsg.umd.edu/SAV, e-mail Maryland Sea Grant atconnors@mdsg. umd.edu, call 301.405.6376, or fax 301.314.5780. To pay bycredit card, order through Maryland SeaGrant’s distributor Cornell Maritime Pressat http://cmptp.com/6647.htm; phone:1.800.638.7641; fax: 410.758.6849.

Non-Profit Org.U.S.Postage

PAIDPermit No. 04386College Park, MD

Maryland Sea Grant College4321 Hartwick Road, Suite 300University System of MarylandCollege Park, Maryland 20740

Address Service Requested

Send us your comments — visit Chesapeake Quarterly Online at www.mdsg.umd.edu/CQ

Chesapeake Quarterly is printed on recycled paper, processedchlorine free, with soy-based inks

New Guide to Underwater Grasses

Documents

CHESAPEAKE QUARTERLY MARYLAND SEA GRANT COLLEGE • VOLUME … · College Park,Maryland 20740 301.405.7500,fax 301.314.5780 e-mail:[email protected] 8 The Culture of Disease A second