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COASTALHERITAGEV O L U M E 1 6 , N U M B E R 3 W I N T E R 2 0 0 1

Triumphof the Weed

COASTALHERITAGE

Triumphof the Weed

2 • COASTAL HERITAGE

TRIUMPH OF THE WEEDThe biological invaders are coming!

WHAT IS “NATIVE”?It’s hard to find a native species in coastal South Carolina.

PHRAGMITES: THE KUDZU OF THE WETLANDS?Some say Phragmites, an invasive plant, is disastrous for

the wetlands of South Carolina. But is it really so bad?

EBBS AND FLOWS

ON THE COVERWater hyacinth (Eichhornia crassipes), an invasive aquatic plant, fills up reservoirs and

clogs waterways. South Carolina bans its importation and sale. PHOTO/WADE SPEES

Coastal Heritage is a quarterly publicationof the S.C. Sea Grant Consortium, a university-based network supporting research, education,and outreach to conserve coastal resources andenhance economic opportunity for the people

of South Carolina. Comments regarding this orfuture issues of Coastal Heritage are welcomed.

Subscriptions are free upon requestby contacting:

S.C. Sea Grant Consortium287 Meeting Street

Charleston, S.C. 29401phone: (843) 727-2078

e-mail: Annette.Dunmeyer@scseagrant.org

Executive DirectorM. Richard DeVoe

Director of CommunicationsLinda Blackwell

EditorJohn H. Tibbetts

Art DirectorPatty Snow

Contributing WriterSusan Ferris

�Board of Directors

The Consortium’s Board of Directors iscomposed of the chief executive officers

of its member institutions:

Dr. Ronald R. Ingle, ChairPresident, Coastal Carolina University

James F. BarkerPresident, Clemson University

Dr. Leroy Davis, Sr.,President, S.C. State University

Dr. Raymond GreenbergPresident, Medical University of South Carolina

Major General John S. GrinaldsPresident, The Citadel

Leo I. Higdon, Jr.President, University of Charleston, S.C.

Dr. John M. PalmsPresident, University of South Carolina

Dr. Paul A. SandiferExecutive Director

S.C. Department of Natural Resources

CONTENTS3

14

7

SLIPPERY CHARACTERS.At a port facility, an inspector withthe U.S. Department of Agricultureexamines imported bananas forpotentially harmful pests.PHOTO/COURTESY OF USDA/APHIS

6

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For ages, a carnivorous jellyfish (Mnemiopsis leidyi)lived in the western edge of the Atlantic Oceanfrom Cape Cod to South America. But nowhere

else. Then one day in 1982 a Soviet research vesseldiscovered the jellyfish in the Black Sea in southeasternEurope. The creature found ideal conditions there: anabundant food supply and few competitors or predators.By 1988, the jellyfish flourished spectacularly, devouringso many Black Sea anchovy eggs and larvae that commer-cial fish catches dropped by 90 percent. How did thejellyfish travel thousands of miles across the AtlanticOcean? International trade carried it abroad, probablyhitchhiking in a ship’s ballast water tanks.

Several years later, a freshwater mussel also caught aride across the Atlantic in ballast water, but it traveled

west, from Europe to America. In 1986, the zebra mussel(Dreissina polymorpha), a native of the Black Sea,suddenly appeared in the Great Lakes, where it repro-duced at an extraordinary rate, clogging industrial andutility pipes. Barges then transported the nuisance musselthroughout the Great Lakes and into rivers from NewYork to Minnesota and as far south as Louisiana andTennessee. Recreational craft carried the mussel intosmaller lakes.

International trade and travel similarly send untoldnumbers of non-native species around the world eachyear. Non-native species are plants, animals, insects, ormicroorganisms carried far from their historic homes.They are also called “exotic” or “alien” or “non-indig-enous” species.

SURVIVAL OF THE FITTEST. The Earth, conservationists say, could become increasingly dominated by hardy, prolific,adaptable “weedy” species such as the green porcelain crab (Petrolisthes armatus).

PHOTO/WADE SPEES

Triumphof the Weed

By John H. Tibbetts

Who’s afraid of biological invaders?

4 • COASTAL HERITAGE

The British ecologist Charles S.Elton first popularized the threatfrom exotic creatures in a 1956 bookThe Ecology of Invasions by Animalsand Plants. Elton argued that “we areliving in a period of the world’shistory when the mingling ofthousands of kinds of organisms fromdifferent parts of the world is settingup terrific dislocations in nature.”Elton warned of an unprecedentedbiological diaspora—creaturesscattered from their native habitatsto foreign lands.

Exotic species are particularlynumerous in North America andEurope, plus Australia and NewZealand. These places have sophisti-cated economies dependent onglobal trade, according to StanfordUniversity ecologist Peter Vitousek.About 24 percent of Canada’s plantspecies and 46 percent of NewZealand’s plant species are exotic. Bycontrast, about three percent ofEgypt’s plant species and one percentof Tanzania’s are non-natives.

Species from abroad slip into theUnited States through every imagin-able pathway. Plant seeds arrive herehidden on farming equipment,packing crates, and other materials.Exotic insects hitchhike on timber,in agricultural produce, and innursery products. Travelers smugglein non-native fruits and vegetablesthat can harbor plant pathogens.Mosquitoes that spread malaria andother diseases travel on cars, planes,railway cars, and trucks. The pet andnursery industries import many alienspecies for aquarium tanks andgardens.

Restless Americans also carryexotics from one part of the countryto another. A species native to theeastern United States can be anuisance west of the Rocky Moun-tains, or vice versa. The marsh grassSpartina alterniflora is a crucialelement in the East Coast estuarinefood chain and provides nurseryhabitat for marine fisheries. Decadesago, to improve habitats, resource

managers introduced this plant to theWest Coast. Wrong move, somebiologists say. The plant has takenover mud flats, displacing valuablefeeding areas for native wading birdsand marine life. “We worshipSpartina alterniflora on the EastCoast,” says James T. Morris, amarine biologist at the University ofSouth Carolina. “But on the WestCoast it’s considered an extremepest,” and resource managers fight it.

In the aquatic realm, ports bearthe greatest brunt of biologicalinvasions. While docked in port, aship will draw water from the estuaryinto special ballast containers. Ballastprovides extra weight, so the shiprides lower in the water and hasgreater stability in the open ocean.

But ballast water isn’t sterile. It’s rifewith fish, jellyfish, clams, mussels, seaslugs, algae, bacteria, and viruses,which can survive a transoceanic triplasting weeks. When a ship enters itsdestination and releases ballast water,a Noah’s ark of small marine crea-tures is flushed into the estuary. Anexotic species can become estab-lished if the new environment issimilar enough to the old one.

Still, very few exotics survivelong in a new environment. Preda-tors eat them. Or exotics starve,unable to compete successfullyagainst natives for food. Many shrivelin inhospitable cold or heat. An

introduced species has to findsuitable conditions—the combina-tion of a satisfactory climate, foodsupply, soil or water type, and a lackof natural diseases, parasites, andpredators.

But at least 6,600 species offoreign origin have became estab-lished in the United States andCanada since Europeans beganexploring and colonizing NorthAmerica five centuries ago. Manyexotic introductions are economicblessings. Nearly every plant cropand all livestock animals cultivatedin North America are descendants ofintroduced species. The only nativeplants raised by American farmersare corn (maize), potatoes, somebeans, squash, sweet potatoes, andsome berries. The turkey, theMuscovy duck, and perhaps one kindof chicken are the only nativedomesticated animals raised in theUnited States, according to ClemsonUniversity historian William F.Steirer, Jr. About 25 percent of fishspecies, including many sport fish, inthe United States are introducednon-natives. American gardens andlawns are covered with non-indig-enous plants, and most of our petsare exotics.

In rare instances, an exoticspecies finds an environment wherenatural enemies are few and it canreproduce and spread aggressively.Ecologists call these creatures“biological invaders,” which causedamage to forests, rangelands, crops,commercial fisheries, recreationaland historic sites, water supplies, andhuman health.

Water hyacinth is among themost troublesome biological invadersin South Carolina. Water hyacinth(Eichhornia crassipes), a fast-growingplant, fills up reservoirs and clogswater supplies. “Some water garden-ers see it as pretty, and it’s a cool-looking plant, but it’s so problematicthat the state has banned its impor-tation and sale,” says Steve deKozlowski, manager of the S.C. Dept

“[W]e are living in aperiod of the world’s

history when the minglingof thousands of kinds oforganisms from different

parts of the world is settingup terrific dislocations

in nature.”

C h a r l e s S. E l t o n

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WEED PATROL. Jim Levesque, a contract herbicideapplicator for the S.C. Dept. of Natural Resources,sprays Roundup on patches of water hyacinth(Eichhornia crassipes) in the Waccamaw River. Waterhyacinth, native to Brazil and introduced to the UnitedStates in the mid-nineteenth century, reproduces rapidlyand forms huge mats that can obstruct waterways.PHOTO/WADE SPEES

6 • COASTAL HERITAGE

CLOSED ECOSYSTEM. Andrew Lohrer, a marine ecologist with the University of SouthCarolina, adjusts one of 48 tubs used to run experiments on native and invasive crabs, their prey,and their predators at the Baruch Marine Laboratory in Georgetown County.PHOTO/WADE SPEES

of Natural Resources (DNR)Aquatic Nuisance Species Program.

People have introduced manyinvaders by accident. The fire ant(Solenopsis invicta) was inadvertentlyimported from Argentina intoMobile, Ala., around 1940 in dryship ballast. Now the imported ant isa major pest in the South and agrowing problem in the Southwest.

Other invaders have beenpurposely introduced with bestintentions. Between 1935 and 1942,the U.S. Soil Conservation Servicegrew 85 million kudzu seedlings,promoted these vines for erosioncontrol, and paid southern farmers toplant them. Since then, the plant hasproliferated throughout the South,covering millions of acres of forests.

Some invaders are difficult tolabel as nuisance or benign. Peoplein one geographic region mightloathe a particular invader, but inanother place they ignore or prize it.Chinese tallow (Sapium sebiferum)—known as the “popcorn tree”—wasintroduced to America in the 1770s.

The tree is found throughout the SouthCarolina lowcountry, where manyregard it as a valuable shade tree. Thestate of Florida, though, bans Chinesetallow because it soaks up moisture fromthe water table.

Some scientists argue that weshouldn’t worry about most alienspecies. Exotics and their humanhandlers have always displaced ordiminished populations of nativeplants and animals, notes Peter DelTredici, a botanist and director ofliving collections at the HarvardUniversity Arnold Arboretum. Asclimate has changed and changedagain, species have adapted, relocated,or died out. “Evolution is aboutsurvival,” he says. “The bottom line ofevolution is, who survives?” WestCoast birds and marine life, forexample, would eventually adapt toSpartina alterniflora and other intro-duced species.

Today’s biological invasions,however, are quite different from thenatural ebb and flow of species overmillions of years, says James T.

What is “native”?

European explorers and colonists beganreshaping North American biology as earlyas the sixteenth century. From thebeginning, Europeans surroundedthemselves with plants from home. In1629, Captain John Smith reported thatmost of the woods around Jamestown,Virginia, had been cut down and “allconverted into pasture and gardens;wherein doth grow all manner of herbs androots we have in England in abundance andas good grass as can be.”

Settlers soon encouraged exotic forageplants such as white clover and a Eurasiangrass that Americans later called Kentuckybluegrass. These plants spread across thecolonies.

The climate has steadily warmed sinceEuropeans arrived here, driving up sealevels and moving salt water farther inland.A brackish marsh that you see near thecoast today was likely a freshwater systemin 1700. Thus entire plant communities—and the animal species that depend onthem—have moved over three centuries.

During the past 75 years, SouthCarolinians have accelerated the scale andintensity of ecological alterations. Majorrivers have been dammed to create lakesfor water supplies, electricity, andrecreation. The water flow into manycoastal rivers has been continuouslymanipulated for various human uses. Urbandevelopment and modern farming havesent excess nutrients into waterways,which have been dredged and altered.

Today few plant assemblages in coastalSouth Carolina could accurately be called“native.” In places like South Carolina thathave a “long history of massive humandisturbance at all levels, the concept thatthere is a plant community that is native tothat area is a biological fallacy,” says PeterDel Tredici, a botanist at Harvard University.

With a few exceptions, resourcemanagers are not really protecting wild,untouched ecosystems from exotic threats.Instead, Del Tredici says, “we are decidingthat ‘native’ species are more valuablethan exotics. And we want to do somethingthat helps encourage ‘natives’ to grow asopposed to (organisms that) we don’t like.That is called gardening.” There’s nothingwrong with gardening, he adds, “but let’snot say that we’re returning things to theirnatural state.”

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Carlton, director of the MaritimeStudies Program of WilliamsCollege-Mystic Seaport inConnecticut. There are two kindsof biological invasions: rangeexpansions (natural movements)and human-mediated introduc-tions. Range expansions flowalong predictable corridors. Bycontrast, modern trade and travelhave allowed people to “dissolveall barriers of time and space,moving species around the world,”says Carlton. “Brazilian estuariesdo not naturally exchange specieswith Japanese estuaries. Buthumans cause species to flow in amatter of hours or days betweensuch areas.”

We have legitimate reasons tofight invaders that cause genuinenuisances such as economic losses,says Mark Sagoff, a philosopher atthe University of Maryland. Butour dislike of some exotics is basedon historical attitudes towardcertain ecosystems. We want tokeep out exotic species that disruptlandscapes and seascapes we havetreasured for aesthetic or culturalreasons. Sagoff argues that “there isno biological property thatdistinguishes native from exoticspecies—it is wholly a matter ofhistory and our preference.”

Many Americans believe,inaccurately, that ecologicalstability is more natural than flux,says Sagoff. And this flawed notionunderpins a misguided preserva-tionist ethic in regard to exoticspecies. The problem is that “wewant ecosystems to stay just as theyare, to freeze nature in time.”

Numerous interest groupslobby fiercely for and againstexotic species. Hunters, birders,boaters, and fishermen shoutwhen invasive species interferewith their hobbies. But sometimeshobbyists fight each other overhow to cope with a biologicalinvasion. Boaters on some SouthCarolina lakes despise Hydrilla

Phragmites: The kudzu of wetlands?

A sturdy weed, growing as high as an elephant’s eye, has invadedGeorgetown County’s freshwater wetlands over the past two decades.Phragmites australis elbows out native plants such as wild rice that provide foodfor migratory birds.

“Phragmites grows so thick that it pushes out aquatic plants that providefood for waterfowl,” says Jack Whetstone, aquatic plant specialist with theS.C. Sea Grant Extension Program.

“Native animals and migratory waterfowl aren’t adapted to Phragmites,”agrees Steven de Kozlowski, manager of the S.C. Dept. of Natural Resources(DNR) Aquatic Nuisance Species Program. “The plant doesn’t provide thefood or habitat that native plants offer. It comes in here and changes thewhole food chain.”

Phragmites has lived along the northeastern U.S. coast for 3,000 years. Noone knows the historical extent of its range, but for most of the twentiethcentury it was a minor part of brackish tideland vegetation. Then in the 1960sand ‘70s, it spread rapidly through the New England coast and south into theMid-Atlantic states. In the early 1980s, it invaded a Georgetown County dredgedisposal site, according to Bob Joyner, manager of the Yawkee Wildlife Center.The weed, which probably hitchhiked south on dredging equipment, hasinfiltrated historic hunting plantations in Georgetown County. “Phragmites isone of the most serious threats we have to our wetlands,” Joyner says.

One morning last August, de Kozlowski pointed out a Phragmites standon the southern end of Sandy Island in Georgetown County. The stand wasso thick that it established a vertical wall of vegetation 15 feet high. “Theweed forms a dense monoculture that spreads and soon you have a huge fieldof this stuff.”

The weed often overtakes small tidal pools where migratory birds searchfor food in the former rice fields along coastal rivers, says Sandra Upchurch, abiologist for the ACE Basin National Estuarine Research Reserve. As a result,ducks have to look elsewhere for nourishment. “The big scare is thatPhragmites can diminish the ecological value of these freshwater areas.”

But sometimes we attack an exotic before we understand how it fits into aparticular niche in an ecosystem, skeptics say. Phragmites could be performingan important job in nature that we don’t yet recognize, says Peter Del Tredici,a botanist and director of living collections at the Harvard University ArnoldArboretum. “A lot of exotic species have been condemned before we’veunderstood how these plants function in an ecosystem.”

Now Phragmites is disappearing in Europe. Ironically, Europeans, whomourn its decline, prize the plant’s capacity to take up excess nutrients. In theUnited States, Phragmites grows rapidly where excess nutrients from urbanizedareas and pollution sources have flooded into coastal areas, says James T.Morris, a marine biologist at the University of South Carolina. “I think it’snutrients,” driving the plant’s success. “Phragmites is responding to a change inthe environment, either high nutrient loads or something else.”

So what would happen if resource managers knocked back the plant toits earlier East Coast range? “If you eliminate that plant,” says Morris, “some-thing else is going to replace it. And the replacement will be less adapted” tocurrent environmental conditions.

South Carolina resource managers, however, worry that if they don’tattack Phragmites stands every year, then it could spread and destroy migratorywaterfowl habitat.

To Joyner, Phragmites is an implacable enemy. And he is outraged thatanyone could see the invader as anything but a menace. “It’s the greatest threatto our marshes, next to sea level rise,” he says. “Anybody who thinks Phragmitesis an advantage ought to lie down and have kudzu crawl over him.”

8 • COASTAL HERITAGE

POP ART. An invasive species can beprized in one region and despised inanother. Holiday wreaths decorated with“popcorn” from a Chinese tallow treehang on a fence in downtownCharleston. The Chinese tallow(Sapium sebiferum) was introduced tothe Americas in 1770s. In SouthCarolina, the tree is admired for itspopcorn-like fruit. Florida, though, bansChinese tallow as an invasive pest.PHOTO/WADE SPEES

verticillata, an invasive aquaticplant, but many fishermen andhunters want to keep it becausethe plant provides food and habitatfor sport fish and waterfowl.

PROFILING INVADERS

Today’s harmless exotic canturn into tomorrow’s nuisance. Some

non-natives lie low for decades orcenturies in their new environmentsbefore causing problems. “Theyarrive and establish small popula-tions,” says Daniel Simberloff, anecologist at the University ofTennessee. “There is a lag time, andthen suddenly they explode. There’sno one answer why. There may be agenetic change or a change in the

environment that makes a speciesmore suitable” in a particularplace.

Someday scientists mighthave the tools to predict whichspecies are likeliest to wreakhavoc. Researchers have alreadyoutlined a number of typicalinvader characteristics, designinga profile of potential troublemak-ers. Some plant nuisances, forexample, have small seeds thatcan spread far and wide. Even so,invaders rarely fall into such neatcategories. “We’re still in theinfancy stage in the science ofpredicting invasiveness,” says DonC. Schmitz, a biologist with theFlorida Department of Environ-mental Protection.

Marine invasions are amongthe most mysterious because weknow far less about marine species’life histories than we do aboutthose of terrestrial creatures.Researchers draw core samplesfrom sediments and identify pollen

records to learn which land plantsexisted in North America beforeEuropeans arrived here. With thisinformation, scientists can judgewhether a plant lived in a particularplace centuries ago.

Such pollen records do not exist inocean sediments. “Our terrestrialcolleagues are much better at findingand understanding invasions than

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INTERNATIONALGATEWAY. Port facilities aremajor pathways for accidentalintroductions of exotic species,particularly via ballast water.

Nations with sophisticatedeconomies based on world

trade are likeliest tocontinue facing threatsfrom invasive species.

PHOTO/WADE SPEES

(marine scientists) are,” saysCarlton. “I don’t have my handsaround a good record” before 1800when the first biologists beganidentifying marine species in EastCoast estuaries. As a result, “wetend to underestimate the real scaleof the invasions and the staggeringnumbers of species moved aroundbefore biologists came on thescene.” Without a long-termhistorical record, scientists can notdetermine whether large numbers ofmarine species are natives ornewcomers.

That’s just the beginning of themystery. Gregory M. Ruiz, abiologist with the SmithsonianEnvironmental Research Center,says that once a marine organismarrives from abroad, scientists“don’t know whether (it) is going toreproduce; if it does reproduce, if itwill persist; how abundant it will beand what impact it will have. Wecan make good guesses, but we can’treally predict how a species is goingto behave in a novel environment.”

A dizzying variety of invadersarrive in American estuaries, bays,and shorelines every year, saysAndrew Lohrer, a marine ecologist

at the University of South Carolina.“People have tried to generalizeabout the broader patterns ofinvasions in the marine environ-ment. But there are many differentways that species, native or exotic,can make their livings in a habitat.”

Some exotics are successfulinvaders because they grow quicklyto sexual maturity, Lohrer pointsout. “They are extremely opportu-nistic, colonizing habitat rapidly andreproducing like mad before they areout-competed by native species.”Other species use a contrastingstrategy. Although growing veryslowly to maturity, they are fiercecompetitors, dominating foodsupplies and other resources.

Many invasive species appar-ently prefer disturbed habitats.Disturbed sites are places whereearth-moving machinery hasdredged up sediments and ripped outvegetation, or places where peoplehave established and maintainedmonocultures such as crops andgrasses.

“It is not any old disturbance”that enables exotics to becomeinvaders, says Simberloff. “It’s placesthat are heavily disturbed (by

humans) on a regular basis that seemto be least resistant to invasions.”Landscapes adjacent to highwayprojects, such as ditches, “are seas ofexotic plants.”

Still, invaders also overtakehabitats that are relatively undisturbedby humans. “Disturbance is not aprerequisite for an invasion,” saysCarlton, but disturbance does offermany exotics a foothold in a newhabitat.

THE UNIQUE AND THECOMMMONPLACE

By mixing species around theworld, people are interfering withevolution, disrupting a natural order,some ecologists say. But skeptics arguethat we’ve affected evolutionaryprocesses since man first began tillingthe soil and raising livestock. Overthousands of years, human beings havetransported species to new places, andpeople have bred plants and domesticanimals to encourage specific traits.

In recent decades, however,people have dramatically acceleratedtheir interference in evolution. Withapplications of antibiotics andpesticides, intense commercial

10 • COASTAL HERITAGE

fishing, and species introductions,“humans may be the world’sdominant evolutionary force,”argues biologist Stephen R. Palumbiof Harvard University in a recentstudy in the journal Science. “Accel-erated evolutionary changes are easyto understand—they derive fromstrong natural selection exerted byhuman technology.” Introducedspecies have caused unusually swiftevolutionary changes in some nativeanimals. Introduced predatory fish,for example, have caused rapidevolution of color patterns and life-history traits in some native fish.

Another question is whetherexotics diminish biological diversityin invaded habitats over the longterm. Biological invasions arecausing an international extinctioncrisis, some ecologists say. Almosthalf of the species on the UnitedStates’ list of threatened or endan-gered species are at risk partly due toexotic invaders. “There is a nearconsensus among scientists thatexotics are the second largestcontributor to species extinction(after habitat loss and degrada-tion),” says Phyllis Windle, a seniorscientist with the Union of Con-cerned Scientists, a nonprofitorganization in Washington, D.C.“And it’s a growing problem.”

The planet, some conservation-ists claim, could become increasinglydominated by hardy, prolific,adaptable “weedy” plants andanimals, such as water hyacinth,Chinese tallow, the zebra mussel, andthe imported fire ant.

Michael L. Rosenzweig, anevolutionary ecologist at theUniversity of Arizona, says thathabitat loss, not biological invasions,will continue to be the primaryculprit for extinctions. Evidencestrongly suggests, he adds, thatevolution, given enough time, wouldrepair the losses of species caused byexotics around the world. Butevolution cannot repair the damagewhen diversity is lost to habitat

degradation. Moreover, invaders usually

increase local biological diversity,says Rosenzweig. “A new speciescomes in, and it often doesn’t pushanybody around. The invaderrestricts the native’s realized (eco-logical) niche. Competition andpredation don’t always result inextinctions; it’s that simple.”

Yes, it’s true that invadersfrequently increase local biodiversity,but we shouldn’t measure an ecosys-tem simply by how many species livethere, argues Carlton. San FranciscoBay is probably the most invadedmarine ecosystem in the world, with250 more species today than it hadin 1850, yet virtually no nativespecies in the bay have been drivenextinct since then. “Exotics haveremoved virtually none of theoriginal species as far as we can telland it’s much richer,” Carlton says.“But it isn’t simply the raw numbersof species that’s important. Nativespecies are in far, far fewer numbersnow, and their role in the ecosystemis vastly reduced. What we havedone is disrupt the way that thesystem once operated. That’s whatwe lament.”

Disruption, though, is a naturalprocess, other scientists say. Naturalevents such as climate changes havealways disrupted how ecosystemsfunction. A warmer or colderclimate, for example, forces speciesto take different roles in an ecosys-tem. “Any ecosystem at any time haslots of common species and a fewrare species,” says Morris. “Whenclimate changes, common speciesoften become rare, and rare speciesbecome common.”

Modern biological invasions,however, are far different from natural

disruptions, Carlton says. Throughballast water and other pathways,exotics are pouring into marinesystems on an unprecedented scalecausing rapid alterations, according toCarlton. And it is not only thefamous invasions that are troubling;the small ones change systems as well.“You can’t put a species into acommunity and not have an impact.It has to eat something, and it has totake up space if it’s a plant or ananimal.”

Equally troubling, says Carlton, isthe idea that invasions seem to createecological conditions that allowadditional aliens to flow in. “Inva-sions beget invasions,” he points out.Eventually, an ecosystem can encoun-ter what some biologists call“invasional meltdowns.” The theory isthat “invasions themselves are adisturbance that disrupts the system,and then you have an opportunity formore invaders.”

Ecologists have found the mostdamning evidence against biologicalinvaders on oceanic islands such asHawaii and other isolated places. Fortens of thousands of years, isolatedislands were cut off from continentalevolutionary processes. Once in agreat while, a storm or freak seacurrent would carry a species—a birdor plant or an insect—from one of thecontinents across the vast PacificOcean to the islands. Most largermammals and reptiles couldn’t survivelong oceanic trips. So remote islandsremained species-poor, lacking manypredators that had shaped continentalecology.

In the nineteenth century,Europeans began introducing speciessuch as rats, snakes, and otherpredators into islands. These intro-duced species consumed native

Web sitesSea Grant Nonindigenous Species Site: www.sgnis.orgU.S. Department of Agriculture: www.invasivespecies.govS.C. Department of Natural Resources Aquatic Nuisance SpeciesProgram: water.dnr.state.sc.us/water/envaff/aquatic/index.html

WINTER 2001 • 11

AGAINST THE WALL. Steve de Kozlowski, manager of theS.C. Dept. of Natural Resources Aquatic Nuisance SpeciesProgram, worries about Phragmites australis stands like thisone on Sandy Island in Georgetown County. Bird huntersdislike Phragmites because it drives out aquatic plants thatprovide food for waterfowl. PHOTO/WADE SPEES

12 • COASTAL HERITAGE

HOLDING BACK THE TIDE. The invasive water hyacinth sends out underwater roots and takes over lakes,reservoirs, bays, and canals. Jim Levesque, a contract herbicide applicator for the S.C. Dept. of Natural

Resources (DNR), sprays on Sandy Island in Georgetown County. PHOTO/WADE SPEES

wildlife, especially flightless birds, whichhad not evolved defensive mechanismsagainst predators.

Exotic invaders pose “an extremelyserious problem in areas that have beenisolated” by seas or by climate, acknowl-edges Del Tredici. “There you have plantsand animals that have evolved in isolation,and when they are exposed to invaders, youcan have a huge extinction crisis.” Remotelakes, surrounded by high mountains, arealso biotic “islands” vulnerable to extinc-tions. Another “island” habitat is thesouthern part of Florida, a subtropicalecosystem cut off by saltwater and climatefrom similar habitats.

After invasions, “islands” often havemore species than before, but the earthoverall has lost biodiversity, ecologists say.The commonplace species has replacedthe unique one.

In North America and other conti-nents, species evolved amongst diversepopulations of predators and pathogens.Thus when biological invaders arrive inSouth Carolina or Massachusetts or Illinois,they are far less likely to cause extinctionsthan invaders in Hawaii or South Florida,

scientists say. “But,” says Lohrer, “there canbe exceptions to this rule.”

STOPPING INVASIVES

Twenty federal resource agencies areresponsible for preventing many biologicalnuisances from entering the country, butmajor loopholes still exist. The U.S. Fishand Wildlife Service requires a specialpermit to import any foreign wild animalsand some nuisance plants, though theagency doesn’t address accidental importa-tion of species. The U.S. Department ofAgriculture’s Animal and Plant HealthInspection Service (APHIS) primarilyregulates species that pose a threat toagriculture and forestry. Yet APHIS usuallydoes not address species that cause prob-lems outside those specialties. Moreover,the federal government has lacked anoverall plan with adequate funding to stopexotic introductions.

In 1990, Congress passed legislation toplug a major loophole—introductions ofaquatic nuisances pouring into the GreatLakes via ballast water. Before ships canenter the Great Lakes, they must now

Contacts

James T. Carlton, WilliamsCollege-Mystic Seaport,(860) 572-5359.

Steve de Kozlowski, SCDNR,(803) 734-9114.

Peter Del Tredici, HarvardUniversity, (617) 524-1718.

Bob Joyner, SCDNR,(843) 546-6814.

Andrew Lohrer, USC,(843) 546-3623.

James T. Morris, USC,(803) 777-3948.

Michael L. Rosenzweig,University of Arizona,(520) 621-7296.

Mark Sagoff, University ofMaryland, (301) 405-4762.

Daniel Simberloff, Universityof Tennessee,(865) 974-0849.

Jack Whetstone, S.C. SeaGrant Extension Program,(843) 546-6321.

Phyllis Windle, Union ofConcerned Scientists,(202) 223-6133.

WINTER 2001 • 13

dump ballast from the previous portat sea and then exchange it withoffshore ocean water. Organismsfrom the open ocean are unlikely tosurvive when discharged intofreshwater lakes or brackishestuaries.

In 1996, Congress passed theNational Invasive Species Act,which reauthorizes the 1990 act.The 1996 law stipulates voluntaryguidelines on ballast water for shipsthat enter all U.S. waters. But thesemeasures aren’t working. Shipscoming into the United States fromoutside the Exclusive EconomicZone, excepting the Great Lakes,are supposed to file reports with theU.S. Coast Guard outlining whatmeasures the ships have taken totreat—that is, exchange—ballastwater. But only about 28 percent ofall ships entering U.S. waters filedthese reports during the period ofJuly 1, 2000 to June 30, 2001, saysLt. JoAnne Hanson of the U.S.Coast Guard EnvironmentalStandards Division. Under thecurrent law, “we have no means toenforce it,” says Hanson. “There areno civil or criminal penaltiesassociated with noncompliance.”

The act is up for reauthoriza-tion in Congress, and some marinescientists and policymakers wantthe law changed to make ballastexchanges mandatory.

In 1999, former President BillClinton signed an executive order tocombat exotics and foster improvedcooperation among federal agencies.The order established an interagencyNational Invasive Species Council,whose members wrote a comprehen-sive plan to minimize the economic,ecological, and human healthimpacts of invasive species anddetermine additional steps toprevent their introduction andspread. The plan includes 57 “actionitems” addressing coordination,prevention, research, and more.

The Bush administration hasnot formally adopted the plan.

“With the shift in administrations,everyone’s waiting to find out whatthe council’s activities will be,” saysSimberloff.

Once a biological nuisancetakes hold in the United States,state agencies have the majorresponsibility to fight it. Yet neigh-boring states often regard a particu-lar exotic species in different ways.South Carolina resource managerssay that water hyacinth is amongtheir worst aquatic nuisances. NorthCarolina, however, does not includewater hyacinth on its list of bannedaquatic plants.

We must vigorously fightdangerous invaders, everyone agrees.But how should we address exoticsthat do not cause a direct economicor human health concern? Shouldwe become more suspicious of allinvaders, a small number of whichcould eventually prove harmful?Should we establish a coordinateddefense of American borders againstevery kind of alien? Or should wewelcome a flood of non-nativecreatures just as earlier Americangenerations did?

Government agencies, conser-vationists say, must provide betterscreening of intentional exoticintroductions for use in gardens,aquariums, and aquaculture. Agen-cies must plug major pathways ofaccidental introductions such asballast water. And governmentmust, of course, fight invaders thatpresent a direct threat to humanhealth, crops, and industries.

Before the 1990s, few peoplenoticed or cared about exoticspecies. Over the past decade,though, many Americans havebecome increasingly alarmed aboutstrange new creatures appearing inour landscapes.

This new concern over exoticsreflects a change in our values, saysCarlton. “A hundred years ago, weoperated under an environmentalethic that (encouraged) movingspecies around to improve nature.

Readings

• Carlton, James T. IntroducedSpecies in U.S. Coastal Waters:Environmental Impacts andManagement Priorities. Arlington,Va.: Pew Oceans Commission,2001.

• Cox, George W. Alien Species inNorth America and Hawaii:Impacts on Natural Ecosystems.Washington, D.C.: Island Press,1999.

• Crosby, Alfred E. BiologicalImperialism: The BiologicalExpansion of Europe, 900-1900.Cambridge: Cambridge UniversityPress, 1986.

• DeVoe, M. Richard (ed).Nonindigenous Estuarine &Marine Organisms. Proceedingsof the Conference and Workshop.Charleston, S.C.: South CarolinaSea Grant Consortium, 1992.(Available upon request.)

• Elton, Charles S. The Ecology ofInvasions by Animals and Plants.Chicago: University of ChicagoPress, 2000.

• Flannery, Tim. The EternalFrontier: An Ecological History ofNorth America and Its Peoples.New York: Atlantic Monthly Press,2001.

• Mooney, Harold A. and Richard J.Hobbs (eds). Invasive Species ina Changing World. Washington,D.C.: Island Press, 2000.

• Palumbi, Stephen R. “Humans asthe World’s Greatest EvolutionaryForce.” Science, Sept. 7, 2001.

• Pederson, Judith (ed). MarineBioinvasions: Proceedings of theFirst National Conference, Jan.24-27, 1999. Cambridge, Mass.:Massachusetts Institute ofTechnology.

• Vitousek, Peter M. et al.“Biological Invasions as GlobalEnvironmental Change.”American Scientist, Sept.-Oct.,1996.

Now we think the absolute reverse.We exist in a time when we have adesire to restore the environment,to do no more harm. Today, wehave a fear of loss, and thatpervades everything we do.”

14 • COASTAL HERITAGE

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Solutions to CoastalDisastersSan Diego, Calif.Feb. 24-27, 2002

Join coastal engineers, scien-tists, and resource managers in SanDiego for Solutions to CoastalDisasters. This conference has beenorganized to foster interdisciplinarydiscussion on disasters. Speakersidentify gaps in informationexchange between researchers andmanagers and offer potentialsolutions to close the gaps. Formore information, visit the Website: www.asce.org/conferences/cd2002

The Coastal Society2002Galveston, TexasMay 19-22, 2002

The Coastal Society’s 2002conference will explore interrelation-ships among the physical, ecological,cultural, and political currents thatconverge at our nation’s coast. Theconference will have three sub-themes: Coastal Watershed andEstuaries; Ecosystem Perspectives atthe Regional Scale; and NationalTreasures and the InternationalCommons. For general informationabout the conference, contact JudyTucker (703) 768-1599 orcoastalsoc@aol.com

6th InternationalConference on ShellfishRestorationCharleston, S.C.Nov. 20-24, 2002

This conference will provide anopportunity for government officials,resource managers, and users to discussapproaches to restore coastal ecosystemsthrough habitat quality assessment andrestoration; stock enhancement, manage-ment, restoration; and habitat remed-iation through watershed management.Those interested in participating shouldcontact Elaine Knight at (843) 727-2078or Elaine.Knight@scseagrant,org Forinformation about submitting an abstractcontact Rick Devoe at (843) 727-2078 orRick.DeVoe@scseagrant.org