Spartina invasion of Pacific coast estuaries in the United States: implications for shorebird conservation JOSEPH
B. BUCHANAN
WashingtonDepartmentof Fish and Wildlife,600 Capitol Way North, Olympia, Washington98501 USA & Cascadia Research Collective,218 • West FourthAvenue, WaterstreetBuilding,Suite 201, Olympia, Washington98501 USA, e-mail:
[email protected]
Buchanan, J.B.2003.Spartinainvasionof Pacificcoastestuaries in theUnitedStates:implications for shorebird conservation.Wader StudyGroup Bull. 100: 47-49. Over the pastcentury,exoticSpartinaspecieshaveinvadedpartsof the Pacificcoastof N America,particularly at Willapa Bay in the stateof Washington,one of the mostimportantshorebirdsitesin the region.The plantsgrow on the tidal flats in densemonospecificstandsandreducethe areaavailableto shorebirds for feeding.In recentyears,the areacoveredby Spartinain Willapa Bay hasincreasedrapidlyandmay posea seriousthreatto thebirds.Thereis anurgentneedto takeappropriate conservation measures to restoreaffected tidal flats and to preventinvasionof Spartinato otherimportantestuaries.
INTRODUCTION
between 1991 and 1995 (Buchanan & Evenson 1997), the typically circularclumpsof cordgrasswere clearly visible,
primarilyin the southernpartof thebay andto a muchlesser extentin scatteredlocalitieselsewhere.The areacoveredby cordgrasswas only about 810 ha in 1994 (Kyle Murphy, pers.comm.),but between1994 and2002, it had morethan tripled (Fig. 1). are found on the northern Pacific Coast of the United States. The increasein the numbersand distributionof Spartina The presenceof cordgrassis considereda detriment to in WillapaBay duringthe 1990swasparticularlydisconcertshorebirdpopulationsin regionswhereit is exotic,having ing becausethe spreadwasrapidandthe areascoveredwere spreadbeyondits normal range. Spartina growsin dense importantsitesfor shorebirds.The surveysconductedbemonospecificstandsand effectively capturesand accumu- tween 1991 and 1995 found that althoughSpartina already latessediment,potentiallygivingriseto increasedelevation coveredpart of the tidal flats at the mouthof the Bear River of the intertidalmudflats (Ranwell 1964). Althoughthe in- in southernWillapa Bay, the sitestill supportedthe greatest fluenceof Spartina on invertebratecommunitiesis neither numbersof shorebirdsin thewholebay with estimatedhighs consistentnor well documented(Daehler & Strong 1996), of 27,260 Dunlins Calidris alpina in winter and 36,900 thedensematsof vegetationreducethe foragingareaavail- WesternSandpipers C. mauriin spring(Buchanan& Evenableto shorebirds,andthishasbeenidentifiedas a possible son 1997). There are no count data for this site from the causeof decreasesin shorebirdpopulations(Goss-Custard periodprior to Spartinainvasion. Eleven sitesor regionsin the bay were includedin the & Moser 1988).The removalof cordgrass from marineestuariesin theregionhasbeenidentifiedasa highpriorityman- aerialsurveys.The top six for winteringDunlins(median= 8,475, range = 3,915-27,260) and four of the top six for agementactivity(Buchananin press). The cordgrass,$. alterniflora, hasinvadedWashington springmigrantWesternSandpipers(median= 14,470,range andhasbecomea problemin someestuaries. HereI describe = 9,600-36,900; Buchanan & Evenson 1997) have been inthe invasionof Spartinaat Willapa Bay and discuss(a) the vadedby Spartina since1995. Cordgrasshasbeenpartially potentialimpactsto shorebirds, (b) ongoingeffortsto remove removed at one of these sites,but the core areas of two sites cordgrass, and (c) potentialimplicationsof continuedinva- are now completelyor largely covered,and five othersites sionthroughthe coastalareasof Washingtonandotherestu- have substantialareasof Spartina.Neither aerialnor groundaries of the northern Pacific coast of North America. basedcountsof Willapa Bay havebeenconductedin winter or springsince1995, so the responseof shorebirdsto these invasions is not known. Two of the individual sites within WILLAPA BAY, WASHINGTON Willapa Bay meet the criteria establishedby the Western Spartinawasfirstrecordedin WillapaBay, anestuaryonthe Hemisphere Shorebird Reserve Network (WHSRN; see southern coastof Washington withanareaof over400km2, Harrington & Perry 1995) for regionally importantsites; in 1894,butwasnotgenerallyrecognized asa potentialprob- Willapa Bay, asa whole,meetsthe criteriaof an internationlem until 1942 (Mumford et al. 1991). For nearly a century ally importantsite (Drut & Buchanan2000). the species' distribution expanded very slowly. When The totalareaof Spartinacoveragein Washingtonis now shorebirdcounts were conductedfrom a small airplane estimatedat about 3,035-3,116 ha (Kyle Murphy, pers. CordgrassSpartina spp.is a commonfeatureof many estuariesalongthe Atlantic coastof North America. Of the 13 speciesfoundin North America,only S.foliosa is nativeto the Pacific coast,where it occursin California (Mobberley 1956). Unfortunately,four speciesof invasiveSpartinanow
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3000
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2000 1500
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Year Fig. 1. Amountof tidalflat area coveredby Spartinaalternifiorain Willapa Bay,Washington,between 1994 and 2002. Data fromWashington Department of Natural Resources database and Kyle Murphy (pers. comm.).
comm.).Most of it is foundin WillapaBay,butperhaps200400 ha existselsewhere,primarilyin northernPugetSound whereS. alternifiora, S. anglica, S. densifioraandS. patens havebeenreported(Daehler& Strong1996).PugetSound is a largecomplexof bothlargeandsmallestuaries thathave collectivelysupported52,000-83,000 winteringshorebirds between1990-91 and1995-96, andperhaps83,000-125,000 springmigrantshorebirds in 1991-94 (Evenson& Buchanan 1997).Spartinahasalsobeenreportedin GraysHarbor,the site of the highest recorded number of spring migrant shorebirdsin Washington:an estimatedone million birds werepresentin 1981(Herman& Bulger1981),and200,000+ havebeenreportedin otheryears(J. Buchanan, unpublished
alongthe Pacific Flyway are thoughtto have experienced populationdeclines(Morrison et al. 2001). Relationships betweenthesesuspected declinesandthepresence or extent of Spartina in Pacific coastestuarieshave not been established.If restoration effortsproveto be largelysuccessful in thenearfuture,thelikelihoodthatanyimpactsto shorebirds would be more than short-term in nature would be reduced.
The coverageof Spartinain Willapa Bay is extensive
ehough thatmanagement efforts involving itsremoval should be referred to in terms of restoration rather than con-
trol. Effortsto remove Spartinathroughmechanicaltilling havebeensuccessful andshorebirds havereturnedto forage in restoredareas.Mechanicaltilling is expensive,however, data). and the level of managementnecessaryto make the transiA simplemodelto assess thevulnerabilityof Pacificcoast tion from the restorationto a controlphasemay take many estuariesto invasionby Spartinawasdevelopedby Daehler years.It is thereforeessentialthat substantialfunding be & Strong(1996). The modelindicatedthat 17 sitesalongthe madeavailableuntil the restorationis complete.A control northernPacific Coast,from HumboldtBay, California, to programmay be neededafter restorationto minimize the PugetSound,Washington,werevulnerableto invasion.Sites likelihoodof significantreinvasion. were consideredvulnerableto invasionif they were both The effectivenessof managementactivitiesin Willapa tidally influencedand protectedfrom wave action.These Bay may have little impacton otherestuariesin the region. criteria typify essentiallyall of the major marineestuaries Willapa Bay is a largeestuarywith severalunitsof a national usedby shorebirdsalong the northernPacific coastin the wildlife refugeandanextensiveareaof commercialshellfish United States.Althoughnot identifiedas a vulnerableestu- beds. In a sense,it is a rather contained area where various aryby Daehler& Strong(1996),theFraserRiverdeltain SW interestgroupshaveforgedpartnerships to address concerns BritishColumbia,Canada,is alsolikely to be a vulnerable aboutSpartinamanagement.The presenceandspreadof site.This is a particularlyvaluableshorebirdsite that sup- Spartinain PugetSoundmay presentsomethingof a differportsvery large numbersduringthe non-breedingseason entchallenge.Many of the estuariestherearesmallandiso(Butler & Campbell1987, Butler 1994). lated,and despitetheir small size collectivelysupport2248% of the over-wintering shorebirdsin Puget Sound in someyears (Evenson & Buchanan 1997). A small number THE OUTLOOK of theseestuariescontainprotectedtidal flats (i.e., a refuge Withoutsystematic surveydata,it is impossible to assess the of somesort) and a few supportlocal shellfishgrowers. potential influence of the current spreadof Spartina on Widespreadinvasionof Spartina in Puget Soundmay be shorebirds. A numberof the shorebirdspeciesthat migrate
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Buchanan: Spartina invasion of Pacific coast estuaries
difficult to reverse becauseof the widely spreadareasof economicvalue(i.e., shellfishbeds)or refugestatus.In addition, moving mechanicaltillers amongthe multiple smaller estuariesmay pose logistical constraintsand require that otherremovaltechniquesbe used.Governmentagenciesand local citizens have begun to monitor a number of Puget Soundestuariesfor indicationsof Spartinapresence.These effortsmay provecrucialto preventingthe establishment of new areas of invasion.
ACKNOWLEDGEMENTS
I thankWendyBrownandKyle Murphyfor providinginformationonSpaminainvasionin Washington. HumphreySitters made commentsthat improvedthe presentation. REFERENCES Buchanan, J.B. In press. Priorities for implementation of the northern Pacific Coastregionalshorebirdmanagementplan. In Ralph, C.J. & T. Rich (editors).Bird conservationimplementationand integrationin the Americas.USDA ForestService,GeneralTechnicalReport. Buchanan, J.B. & J.R. Evenson. 1997. Abundance of shorebirds at Willapa Bay, Washington. WesternBirds 28: 158-168. Buffer, R.W. 1994. Distributionand abundanceof WesternSandpipers, Dunlins, and Black-belliedPloversin the FraserRiver estuary.Pages 18-23 in Butler, R.W. & K. Vermeer (editors). The abundance and distributionof estuarinebirds in the Strait of Georgia, British Columbia. CanadianWildlife ServiceOccasionalPaperNumber83.
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Buffer, R.W. & R.W. Campbell. 1987. The birds of the Fraser River delta: populations,ecologyand internationalsignificance.Canadian Wildlife ServiceOccasionalPaperNumber 65. Daehler, C.C. & D.R. Strong. 1996. Status,predictionandpreventionof introducedcordgrassSpartina spp.invasionsin Pacific estuaries,USA. Biological Conservation78:51-58. Drut, M.S. & J.B. Buchanan. 2000. U.S. National shorebirdconservation plan:northernPacific coastworkinggroupregionalmanagement plan. Portland,Oregon. Evenson,J.R. & J.B. Buchanan. 1997. Seasonalabundanceof shorebirds at Puget Soundestuaries.WashingtonBirds 6: 34-62. Goss-Custard,J.D. & M.E. Moser. 1988. Ratesof changein the numbersof Dunlin Calidris alpina winteringin British estuariesin relation to the spreadof Spartina anglica. J. App. Ecol. 25: 95-109. Harrington, B. & E. Perry. 1995. Important shorebirdstaging sites meetingWesternHemisphereShorebirdReserveNetwork criteria in the United States. USDI
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Herman, S.G. & J.B. Bulger. 1981. Distribution and abundance of shorebirdsduring the 1981 springmigrationat Grays Harbor, Washington.U.S. Army Corpsof Engineers,contractreportDACW67-81M-0936. Seattle,Washington. Mobberley, D.G. 1956. Taxonomyanddistributionof the genusSpartina. Iowa State College J. Science30:471-574. Morrison, R.I.G., Y. Aubry, R.W. Butler, G.W. Beyersbergen,G.M. Donaldson, C.L. Gratto-Trevor, P.W. Hicklin, V.H. Johnston & R.K. Ross. 2001. Declinesin North American shorebirdpopulations. Wader Study Group Bull. 94: 34-38. Mumford, T.F., Jr., P. Peyton, J.R. Sayce& S. Harbell (editors). 1991. Spartina workshoprecord. WashingtonSea Grant Program,University of Washington,Seattle,Washington. Ranwell, D.S. 1964. Spartinasaltmarshes in southernEngland,II, rateand seasonalpattern of sedimentaccretion.J. Ecol. 52: 79-94.
Developmentof Spartinameadowon formerlyopen mud flats at Willapa Bay, Washington,USA. Photo by Blain Reeves.
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