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The relation between distribution of zooplankton and salinity in the Changjiang Estuary

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The relation between distribution of zooplankton and salinity in the Changjiang Estuaryof,in,The,and,the

    The relation between distribution of zooplankton and salinity in the Changjiang

    Estuary

    ChineseJournalofOceanologyandLinmology

    Vo1.26No.2,E178185,2008

    DoI:10.1007/s0034300801781

    Therelationbetweendistributionofzooplanktonand

    salinityintheChangjiangEstuary一一一一

    GAOQian(高倩),,,xuZhaoli(徐兆礼),,ZHUANGPing(庄平)"

    tlnstituteofOceanology,ChineseAcademyofSciences,Qingdao266071,China tKeyandOpenLaboratoryofMarineandEstuaryFisheries,MinistryofAgricultureofChina,EastChindSeaFisheries

    ResearchInstitute,ChineseAcademyofFisheriesSciences,Shanghai200090,China GraduateUniversityofChineseAcademyofSciences,Beijing100038,China ReceivedApr.19,2007;revisionacceptedSept.12,2007

    AbstractSeasonalnetzplanktonsamplesfromstationsintheChangjiang(YangtzeRiver)Estuary

    werecollectedfromMay,2004toFebruary,2005.Thedominantspeciesandtheircontributiontothe

    totalzooplanktonabundanceweredetermined.Moreover,therelationshipbetweenthesalinityand

    abundancewasstudiedwithstepwiselinearregression.Duringthewholeyear,thesalinitywaspositively

    correlatedwiththeabundance.whilethetemperature.negatively.Linearregressionanalysisshowedalso

    ahighpositivecorrelationwithsalinityfortotalabundanceinAugustandNovember,whilein

February

    andMay,noobviousrelationswerefound.Themostabundantcommunitywascomposedofneffticand

    brackish

    waterspecies.TheNorthPassageCNP)(salinity<5)wasgreatlydilutedbyfreshwaterwhilethe

    NorthBranchfNB)wasbrackishwaterwithsalinityrangeof12-28.Consequently.cleardeclinein

    abundanceofzooplanktonwasalongtheestuarinehaloclinesfromthemaximumintheareaofhigh

    salinitytotheminimuminthelimneticzone.Totalzooplanktonabundanceandbiomasswerelowerin

    NPthantheNBinallseasons.Inshort.thesalinityinfluencedeabundanceofeachspeciesof

    zooplankton,andultimatelydeterminedthetotalabundanceofzooplankton.Furthermore,awinterpeak

    intheabundanceexisted,whichmightbecausedbytheflourishingofSinocalanussinensis,awidely

    distributedspeciesintheChan~iangEstuary.

    Keyword:salinity;Changjiang(YangtzeRiver)Estuary;zooplankton;abundance;dominantspecies

    lINTRODUCTION

    TheChangjiang(YangtzeRiver)Estuary,a

    meso-tidalestuary.isfamousforlargerunefrandhigh

    suspendedsedimentconcentration.Anestuaryisa

    placewhereriversmeettheseaandhydrological

    characteristicschangesviolently,especiallyinsalinity

    thatisanimportantfactorcontrollingdissolved

    oxygen(D0),nutrients,andproductivitytosome

    contents,andfurthermore,affectthedistributionof

    estuaryorganismsinhorizonmldirection(Perkins,

1974;Zheng,1982).

    Obviously,thesalinityinanestuaryiscrucialto zooplankton.Howzooplanktoncommunitiesreactto thesalinityisahottopicforscientists.Ingeneral,the numberofspeciesinestuaryissmallerthanthatin marineenvironment(Remane,1971).Thebiotaof estuarineareasislargelymadeupofeuryhaline marinespecies(Gunter,1961),andrelativelyfewer t~eshwaterspeciesoccurevenatlowsalinities(Kinne, 1971;Remane,1971).IntheJiulongEstuary(Fujian Province),HuangandZheng(1987)andShangeta1. (2005)studiedcopepodcommunitiesalonghorizontal salinitygradients,andfoundthatspeciesdiversity increasedwithsalinityincrease.Martin(2002) pointedoutthatsalinityvariationinfluencedthe distributionoforganismsintheestuaries.Inthe ZhujiangEstuarythatenterstotheSouthChinaSea, significantspatialvariabilityinzooplankton abundanceandbiomasswasduetoincreasein

    horizontalsalinity(Lieta1.,2006).Islameta1.(2005) foundthatalongsalinitygradientthereweredifferent environmentsintheturbiditymaximumofthe

    estuarinesystemintheAriakeSea.T1us.totally

    differentcommunities..——oligohalineandeuryhaline

    oneswerefound.Therefore,salinityimpactsthe communitiesofzooplanktonconsiderablyinestuary. SupportedbytheMajorResearchPlanoftheNatura1Science FoundationfNSF)ofChina(No.905l1005),MajorProgramofNSFof China(No.30490234,WP4003),ResearchProjectofShanghaiYangtze EstuarineNatura1ReserveforChineseSturgeonandSpecialResearch

    ProiectoftheMinistryofScienceandTechnologyofChina(No. 2003DIB4Jl29)

    Correspondingauthor:xiaomin@public4.sta.net.cn

No.2GAOeta1.:TherelationbetweendistributionofzooplanktonandsalinityintheChangji

    angEstuary179

    IntheChangiiangEstuary,mostpreviousstudiesin estuaryhavebeenlimitedtothespeciescomposition, dominantspecies,seasonalcommunitysuccession, andsoon(Zhu,1988;Cheneta1.,1995a,b;Xueta1., 1995,1999a,b;Guoeta1.,2003;Zhangeta1.,2005; Xu.2005;XuandShen,2005;JiandYe,2006). However,fewconcemedhowsalinityaffects dk,;tributionandabundanceofzooplankton. TheinvestigationareawasOffChongmingIsland, nearthemouthbaroftheestuary.Accordingto hydrographyandzooplanktonspeciescomposition, theareawasdividedintotworegions--——NorthBranch

    (NB)andNorthPassage(NP)(Kongeta1.,20O4). Relationshipofthesalinitytotheabundanceand distributionofzooplanktonwasstudiedforunder- standingthephysiologicalecologyofzooplankton. 2MATERIALANDMETHoD

    2.1Studyareaandsamplingmethod

    SamplingintheChangjiangEstuarywasconducted infourcruisesrepresentingfourdifferentseasons: spring(May2004),summer(August2004),autumn (November2004)andwinter(February2005).The samplinggridwascomprisedof16stationsineach survey,inwhichStations1,2,3,6,9,10,14,and16

    wereintheNP,andtheothersintheNB(Fig.11.The tworegionswereneareachother.butthesalinityand zooplanktonspeciescompositionwereverydifferent. Temperaturewasstable,andsodidnutrients(Shen andPan,2001:TuandWang,2006).

    Sampleswereverticallytowed.withanopening. closingstandardlargenetrdiameter50cm.meshfiber GQ14,meshsize0.505mm),fromthebosomtothe surface.Thevolumeofwaterwasmeasuredbyaflow meter.Zooplanktonsampleswerepreservedin5% formalin,identifiedtospecieslevelundera stereomicroscopy,andtheabundanceofeachspecies 32

    N

    31.5

    3l

    305

    wascalcu1ated.TheunitOfabundancewasind/m3and theunitofbiomass(notincludeMedusaeand Thaliacea)wasmg/m.Foratechnicalreason,the Station11wasnotinvestigatedinAugust. 2.2Dataprocess

    Thedominance(1,)ofeachspeciesidentifiedby ZhaoandZhou(1984)wascalculatedwiththe fo~owingequations:

    rni/N)xf,

    ?1ereniistheabundanceofspecies,isthe occurrencefrequencyofspecies,andNisthetotal abundance.O.02woulddenoteadominantspecies inacommunity(XuandChen,1989).

    Thecontributionofabundanceofeachdominant speciestototalabundanceofzooplanktonwas determinedbyastepwisemultipleregressionofthe totalabundance(thedependantvailable)onthe abundancesofindividualdominantspecies(the independentvailables)(ChenandWang,1987).The stepwiseregressionwasalsocarriedoutbetweentotal abundanceandthesurfacetemperatureff)orsurface salinity((ChenandWang,1987;XuandLi,2006). 3RESULT

    3.1Relationofsalinitytootherhydrological factors

    Largedifferenceswereobservedinsurfacesalinity inthestudyareaduringfoursurveys(Fig-2).Ahigh salinitycenter(14.61intheNPwasnoticedduring springtideofAugust.Inotherseasons,salinity maximumoccurredintheNB.FromNPtONB.the salinityincreasedconsistently.Theaveragesalinityin NovemberwasslightlyhigherthanthoseinFebruary orMay.InAugusttheaveragesalinitywasthelowest ofal1.Theaveragesalinityreadingsofspringtide Fig.1MoftheChangjiangEstuarywithsamplingstations (NBstandsforNorthBranch,NPf0rNorthPassage)

180CHIN.J.OCEANOL.LIMNOL.,26(2),2008

    werehigherthanthatofneaptide:howevertheir horizontaldistributionsweresimilar.Becausethe depthwasfairlysmallandthemixingwasstrong.the salinityshowednosignificantdifferencesbetweenthe surfaceandbottomwater.InNP.thesalinitywas<5

    a1lyearlong,WhileinNB,thesalinityranged differently:May(13.2_22.1),August(3.4.20.5), November(22.38.5),andFebmary(11.6_27.4). Spatiallythetemperaturewasstable:thesurface temperaturewasclearlylowerinFebruary(5.7?0.8.C1

    thanthoseinNovember(16.3?0.4.C),May

    (21.8?1.oC),andAugust(28.3?1.oC).NPandNB

    arenotfarfromeachother,asaresult,exceptsalinity, thephysicalcharacteristicssuchastemperature,SSL, nutrientsvariedonlyslightly.

    3.2Horizontaldistributionofabundance

    Horizontalabundanceswereobviouslyuneven Vb1.26

    (Fig.3).InMay,atspringtide,theabundancecentre appearedinNP:whileatneaptide,itwasinNB.The dominantspecieswereMonoculodesfimnophilus, Schmackeriapoplesia,TortanusveFmiculusand Labidoceraeuchae,reachinghighofl750.0ind/m insalinityof15.9.FromSOUthtOnorth,thegreaterthe salinitywas,thehighertheabundancewas.Moreover thereexistsaseasonalalterationofdominantspecies. InAugust,S.poplesia,Acartiapacca,and

    veFmiculusweredominant,WhileinNovember,at springtide,Leuchaeta,Paracalanusparvus,andp, aculeatusdominatedreachingthehighestabundance Ofl226.7ind/m,andatneaptide,Pparvuswasthe onlydominantspecierl036.7ind/m').Sinocalanus sinensisandAcartiahongiwerenormallyflourishedin Febmary(winter),atneaptide,theabundancewas 8080.0and2960.0ind/m~forthetwospecies.

respectively.

    Fig.2Horizontaldistributionofsalinityindifferentseasonsandtideperiods

No.2GAOeta1.:TherelationbetweendistributionofzooplanktonandsalinityintheChangji

    angEstuary181

    Fig.3Horizontaldtstributionofabundance(ind./m.)indifferentseasonsandtideperiods

    3.3Seasonalchangesinabundanceandbiomass ofzooplankton

    Thezooplanktonabundanceoftheinvestigated watersexperiencedFebruarypeak(2094.3ind/m).In otherseasons,theywerealmostatthesameorderof magnitude(Fig.4),v/z.Novemberat428.9ind/m, Mayat392.9ind/m.,andAugustat283.6ind/m.The seasonalbiomassvariedinthesamepattem.Ingeneral, theabundanceandbiomassOfNBwerehigherthan thoseofNP.

    3.4Seasonalcontributionofpredominantspecies tototalabundance

    InTable1,theregressionindexBindicatesthe contributionoftheabundanceofaspeciestothetotal abundance.InMay,thedominance(0.34)and abundance(120.6ind/m3)ofLcwerethe

    highestintheNByetitsregressionindexBwas0.34 lessthanthatof^imnophilusat0-47.IntheNP. sinensiswasthemostimportantspeciesindominance, abundance,and8value.InAugustS.sinens&wasthe highestinabundanceanddominance,butthe contributionofA.pacificatothetotalabundancewas higherthanthatofsinensis.InNovember,inNB parvuswasthemostabundant;andinS.sinens

dominated.InFebruary,theestuarywassimply

    dominatedbysinens&.

    3.5Relationshipbetweenaboticfactorand

    abundance

    LinearregressionshowedahighlYpositive

    correlationbetweensalinityandtheabundancein AugustandNovember,butFebruaryandMayhadno

    significantrelations.Duringthewholeyear,the abundancewaspositivelycorrelatedwithsalinity, whilenegativelycorrelatedwithtemperature.

182CHIN.J.

    OCEANOL.LIMNOL.,26(2),2008

    Fig.4Regionalandseas0naldistributionofbiomassandt0talabundance

    (Unit:ind/m.;NBstandsforNorthBranch,NPforNorthPassage) Table1Contributionofabundanceofdominantspeciestototalabundance

    MonthDominantspecies

    YY

    May

    August

    November

    inocalanussinensis0.0416.20.113.380.67155.90.7731.18 Schmackeriapoplesia0.0630.2.0.01.0.10.027.20.052.42* Labidoceraeuchaeta0.34122.60.345.57

    Tortanusvermiculus0.1147.60.272.1600727.50.312.48 Monoculodesfimnophilus0.0654.70.475.00

    Limacinatrochiformis0.0215.80.020.57

    poplesia0.38158.6O.726.09

    Acartiapacca0.2594.90.2413.580.164.30.915.78* vermiculus0.1868.00.28.42

S.sinensis0.265.50.510.93

    Brachyurazoea0.020.80.O40.76

    Calanussinicus0.0419.80.055.08

    S.sinensis0.69113.50.98129.45

    Paracalanusparvus0.31176.107884.18

    P.aculeatus0.27142.10.4747.75

    Leuchaeta0.1789.70.2317.600.036.500912.32 vermiculus00213.50.086.76*

    sinensis0.721435.40.7444.63077362.90.97205.20 FebruaryAcartiahongi0.15360.20.2917.800.029.00.024.15 Limnoithonatetraspina0.0631.30.0713.79 Yisdominantspecies;ismeanabundance(ind/m),standardregressindex)indicatesthecontri

    butionofaspeciesto

    totalabundance;istheresultoft-testfP<O.O1:P<0.05)

    4DISCUSSION

    4.1Salinityandotherenvironmentalfactors Spatialdistributionpatternsofsalinitywereobvious. TheNPwascharacteristicoffreshwaterinsalinity below5:NB,however,hadhighersalinityofl228

    (Fig.21inallseasonsexceptofAugust.NPwasthe majorchannelforca.50%oftheseawardflowofriver water,whileNBtookonlyl%(Shen,2001).InoveralI, thesalinityincreasedfromthesouthtothenorth. Clearly,thesalinitychangesseasonally,higherin dn,seasonsandlowerinfloodseasons,showinga clearrelationshiPbetweenrunoffandsalinity. Vbl-26

    Generally,partsoftheestuarywereoccupiedby certainspecieslivinginthewaterdependedupon runofffromtherivers.Althoughthestudyareawas

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