NewZealandMudsnails:EffectsonNativeHydrobiidSpecies,ReproductionafterDigestionbyFish,andUpdateonRangewithinUtah

RandyOplingerandEricWagner

UtahDivisionofWildlifeResourcesFisheriesExperimentStation

1465West200NorthLogan,UT84321

July2016PublicationNumber16-13GregorySheehan,Director

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TableofContentsExecutiveSummary.....................................................................................................................................3

Task1:EffectoftheInvasiveNewZealandMudsnailontheBehaviorofTwoNativeSnails......................4

Task2:EffectoftheInvasiveNewZealandMudsnailontheRecruitmentandSurvivalofTwoNativeSnails..........................................................................................................................................................16

Task3:RecruitmentPotentialAmongNewZealandMudSnailsthatSurviveFishDigestion...................22

Task4:UpdateoftheRangeofNZMSwithinUtah...................................................................................27

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ExecutiveSummary

Weworkedonfourtasksthatwereintendedto:a)improveourunderstandingoftheeffectsthatinvasiveNewZealandmudsnails(NZMS)haveonnativesnails,b)determinewhetherNZMSthatsurvivepassagethroughfishdigestivetractscanreproduce,andc)updateourunderstandingonthedistributionofNZMSwithinUtah.

Inthefirsttask,wedeterminedtheeffectthatNZMShadonthebehavioroftwonativehydrobiidsnailspecies;theToquervillespringsnailPyrgulopsiskolobensisandthemudamnicolaAmnicolalimosus.Toaccomplishthis,weestablishedtestarenathatcontainedvariousdensitiesofthenativesnailsandNZMS.WevideorecordedthemovementsofthesnailsandcomparedmovementsofthenativesnailsbothbeforeandaftertheadditionofNZMStothearena.WefoundthattheadditionofNZMSdidnotaffectthenetdistancethatthenativesnailsmovedduringthetrials.ThedistanceseparatingthenativesnailsfromconspecificsdidnotchangewhenNZMSwereadded.Thenativesnails,however,tendedtospendmorecumulativetimeclosertoconspecificsthantoNZMSandthistendencytobeclosertoaconspecificincreasedasthenumberofNZMSwithinthetestarenaincreased.

Inthesecondtask,weevaluatedtheeffectsofNZMSonthesurvivalandrecruitmentofthesametwonativehydrobiidspeciesevaluatedinthefirsttask.WefoundthatthepresenceofNZMShadnoinfluenceonthesurvivalofthenativespecies.NewZealandmudsnailsproducedmorerecruitsandahighernumberofrecruits/adultthanthenativespecies.ThisresearchdemonstratesthatthehighinvasionratesofNZMScanatleastbepartiallyexplainedbytheirhighrecruitmentrates.

Inthenexttask,wefedNZMStorainbowtroutfromtwosizeclasses(averagetotallength141and207mm,respectively).ThesurvivingNZMSwereharvestedandtheneonateproductionamongthesesnailswasevaluated.WefoundneonateproductionamongNZMSthatweredigestedbybothsizeclassesoffish.TheresultsindicatethatNZMSthatsurvivedigestionarenotsocompromisedthattheycanreproduce.ThisshowsthatextremecautionshouldbetakenwhenstockingfishfromhatcheriesthatcontainNZMS.

Inthefinaltask,wesurveyedPosey,WideHollow,UpperBoxCreek,andLowerBoxCreekReservoirsforNZMSanddidnotfindthesnailinanyofthesereservoirs.WepresentanupdatedmapshowingthedistributionofNZMSwithinUtah.

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Task1:EffectoftheInvasiveNewZealandMudsnailontheBehaviorofTwoNativeSnails

Background

NewZealandmudsnails(NZMS)Potamopyrgusantipodarumareanexampleofasuccessfulinvasivespecies(AlonsoandCastro-Diez2008).Onceestablished,NZMScanbecomeadominantcomponentofaninvertebratecommunityandconsequently,NZMShavetheabilitytonegativelyaffectothertaxa.Forexample,severalstudieshavefoundthatthegrowthratesofothersnailtaxaaresuppressedinthepresenceofNZMS(KristandDybdahl2005;RileyandDybdahl2015).Rileyetal.(2008)foundthatNZMSlimitedthegrowthofthenativesnailPyrgulopsisrobustaandthatthenativesnailfacilitatedthegrowthofNZMS.StudieshavealsofoundtheabundanceofotherinvertebratetaxatocovarywithNZMSabundance(Keransetal.2005;Mooreetal.2012).Finally,NZMShavebeenshowntoalterthebehaviorofotherspecies.Forexample,Keransetal.(2005)foundthatotherspeciesofmacroinvertebrateswerelessabundantontilesthatwereheavilycolonizedbyNZMS.Keransetal.(2010)foundthatNZMSinterferedwiththeforagingofmayfliesinthefamilyBaetidaebutthatthecaddisflyBrachycentrusoccidentaliscausedNZMStoabandonthesurfacesoftiles.ThepresenceofNZMShasalsobeenassociatedwithshiftsinfeedingpreferencesintheisopodAsellusaquaticus(Aberleetal.2005)andbaetidmayflies(Keransetal.2010).

NewZealandmudsnailsaremembersofthesnailfamilyHydrobiidae,whichisthelargestfreshwatermolluskgroupwithmorethan1,000species(HershlerandPonder1998).Manyspecieswithinthefamilyhavespecifichabitatrequirements,limitedranges,andaresensitivetohabitatalteration(HershlerandPonder1998).Consequently,manyhydrobiidspeciesareconsideredthreatenedorendangered(e.g.,BlissRapidssnailTaylorconchaserpenticola;Richards2004).TheeffectsthatNZMShaveonotherhydrobiidtaxaarepoorlyunderstoodbutsimilaritiesinbodysize,habitat,andlife-historyrequirementswouldsuggestthatNZMScouldhavestrongercompetitiveeffectsonotherhydrobiidspeciesthanotherinvertebratetaxa.

ThegoalsofourresearchweretoassesshowNZMSaffectthebehavioroftwootherhydrobiidspecies,theToquervillespringsnailPyrgulopsiskolobensisandmudamnicolaAmnicolalimosus,bothofwhicharenativetotheUnitedStates.TodothisweplacedP.kolobensisorA.limosusalongwithvaryingdensitiesofNZMSwithinPetridishesandvideotapedtheinteractionsamongthesnails.WedeterminedhowNZMSaffectedthemovementofthenativesnailsandwhetherthenativesnailspreferredtocongregatenearconspecificsoverNZMS.WehypothesizethatthepresenceofNZMSwouldreducethemovementofnativesnailsandforcenativesnailstocongregatewithconspecifics.

Methods

SnailCollectionandMaintenance

Pyrgulopsiskolobensis,A.limosus,andNZMSwerecollectedinthefieldandtransportedtotheUtahDivisionofWildlifeResource'sFisheriesExperimentStation(FES;CacheCounty,Utah).Snailsweretransportedin4.0Lvolumeplasticbagsthatwerefilledwith1-2Lofwaterandnaturalvegetationfrom

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thecollectionsites.Bagswerefilledwithoxygenandtransportedincoolerswithice.P.kolobensiswerecollectedonJuly28,2015fromasmallspringsituatedonNationalForestlandnearPineValley,Utah(WashingtonCounty).MudamnicolawerecollectedonAugust3,2015fromtheRightHandForkoftheLoganRiver(CacheCounty,Utah).NZMSwerecollectedonJuly27,2015fromtheLoaStateFishHatchery(WayneCounty,Utah).UponarrivaltoFES,snails,water,andcollectionsitevegetationweretransferredtoplasticaquaria(35x21x12.5cm,lengthxwidthxheight)withoneaquariumusedperspecies.Anairstoneconnectedtoanaquariumairpumpwasusedtoaeratetheaquariaandwerestoredinarefrigerator(FrigidaireElectroluxFFHT2021QW10,Charlotte,NorthCarolina,USA)withaon/offcyclecontrolledbyatemperaturecontrolswitch(JohnsonControlsmodelA419ABG-3,WestValleyCity,Utah,USA).Thetemperatureintherefrigeratorwassetat6°Candaveraged5.2±2.3°C(mean±SD;measuredevery15minwithaHoboOnsettemperaturelogger,Bourne,Massachusetts,USA).WaterexchangeswereperformedtwiceweeklyusingFESwellwater(pH=7.2,hardnessandalkalinity=200mg/L).Toprovidefood,watercressNasturtiumofficinalewasperiodicallycollectedfrombelowtheFESfishhatchery,rinsed4-5xwithwatertoremoveotherinvertebrates,andaddedtotheaquaria.

VideoCollectionApparatus

FourLogitechc525webcameras(Newark,California,USA)weremountedonashelfwithinthesamerefrigeratorwheretheaquariawerestoredandthesecameraswereaimeddownwardtocaptureimagesonashelfthatwas32cmbelow.Thewebcameraswereattachedviafourseparateuniversalserialbus(USB)connectorstoaHewlettPackardCompaq8510plaptopcomputer(PaloAlto,California,USA)thatwassituatedoutsidetherefrigerator.ThewebcamerasweremanagedandvideoswerecapturedusingiSpyvideosurveillancesoftware(version4.1.9.0;http://ispyconnect.com).ThedefaultiSpysettingswereused,exceptthesoftwaresettingswerechangedtocaptureoneimageeverysecond.VideoswerecapturedusingiSpyinaMP4format.TheywerethenconvertedtoaWindowsMediavideofile(WMVformat)usingMicrosoftLiveMovieMaker(2011Version;Redmond,Washington,USA).DecompileVideoMasterversion1.8(http://audane.com)wasusedtoseparatetheWMVfilesintoseparateJPGimageswithoneimagecapturedevery10seconds.Finally,MakeAVIsoftware(http://makeavi.sourceforge.net/)wasusedtocompress/converttheJPGimagesintoasingleAVIformatvideo.AVIfileswereprocessedusingthe"ManualTracking"plugininImageProcessingandAnalysisinJava(ImageJ)software(http://imagej.nih.gov/ij/).

ExperimentalDesign

ExperimentaltrialsweredesignedtoassesstheeffectsthatNZMShaveonthetwonativespecies.Trialslasted48hrswiththefirst24hrsservingasacontrolperiodwherethreeindividuals,allfromthesamespecieswereinatestarena.Afterthecontrolperiodwascomplete,1,3,or6individualsfromeitherthesamespeciesorNZMSwereaddedtothearenaswithfivereplicatesofeachcombinationtested.Thus,thetreatmentsfortheP.kolobensiswerethreeP.kolobensisforthefirst24hrsfollowedbytheadditionof1,3,or6P.kolobensisforthesecond24hrs.Alternatively,1,3,or6NZMSwereadded.Similarly,1,3,or6A.limosusor1,3,or6NZMSwereaddedfortrialsthatbeganwithA.limosus.OnlyNZMSwereaddedafter24hrstoarenasthathadNZMSforthe24hrcontrol

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period(1,3,or6individualsadded).Testarenaswere150mmdiameterPetridishesfilledwith25mLofFESwellwateranda1cm2pieceoffresh,organic,storepurchasedspinachSpinaciaoleraceawasaddedtothePetridishestoprovidethesnailswithforage.Snaildensitiesduringthefirst24hrswere170individuals/m2andwere226,340,or509individuals/m2duringthesecond24hrsdependingonwhether1,3,or6individualswereadded.Eachwebcamerarecordedasingletestarena.Atotalof75videoswererecordedandrecordingsbeganonAugust10,2015andwereshotatfourvideosatatimeuntilallvideoswererecorded.Topreventbias,theorderthatthevideoswererecordedwasrandomizedamongtreatmentsandindividualsnailsonlyparticipatedintherecordingofasinglevideo.

VideoProcessing/StatisticalAnalysis

TheprocessingofthevideosfollowedtechniquesthataresimilartothosedescribedinMyrick(2009).Eventhough48hrsofvideowasrecordedforeachreplicate,onlyfourhourswasfurtherprocessed.Wedecidedtoprocessthesecondandlasthourofvideofromeach24hrperiod(i.e.,hours2,24,26,and48).Thesetimeswereselectedtorepresentbehaviorchanges(e.g.,tiring)acrosstheentireobservationperiodandwewantedtogivethesnailsatleastonehourtoacclimateafteradditiontothetestarenas.Regardlessthatweonlyobservedfourhoursofvideo,individualsnailswerefollowedbywatchingthevideosatacceleratedspeedsoindividualsthatparticipatedintheinitial24hourcontrolperiodcouldbeseparatedfromtheadditionalsnailsthatwereaddedafter24hrs.

Thepositionofthesnailswastrackedusingthe"Manualtracking"plugininImageJandcoordinateswerecopiedintoaMicrosoftExcelspreadsheet(Redmond,Washington,USA).Coordinatepositionwasdeterminedevery10s(sinceimageswerecapturedofftheoriginalvideosevery10s).Pixelcoordinateswereconvertedtomillimetercoordinatesusingtheformula(Myrick2009):

𝑐𝑜𝑜𝑟𝑑𝑖𝑛𝑎𝑡𝑒 𝑚𝑚 = 𝑐𝑜𝑜𝑟𝑑𝑖𝑛𝑎𝑡𝑒 𝑝𝑖𝑥𝑒𝑙𝑠 × 𝑚𝑒𝑎𝑠𝑢𝑟𝑒𝑑 𝑤𝑖𝑑𝑡ℎ 𝑜𝑓 𝑎𝑟𝑒𝑛𝑎 (𝑚𝑚)𝑚𝑒𝑎𝑠𝑢𝑟𝑒𝑑 𝑤𝑖𝑑𝑡ℎ 𝑜𝑓 𝑎𝑟𝑒𝑛𝑎 (𝑝𝑖𝑥𝑒𝑙𝑠)

Then,coordinateswereconvertedtodistancesusingtheformula(Myrick2009):

𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒!!! = 𝑥!!! − 𝑥! ! + (𝑦!!! − 𝑦!)!

wherexi+1andxiarethex-coordinatesandyi+1andyiarethey-coordinates.

Thedistancestraveledduringeach10sincrementweresummedtodeterminethecumulativedistancetraveledinanhour.Inaddition,thedistancetothenearestconspecificsnailandNZMSwasdeterminedforeach10sincrementandwereaveragedforeachhour.Thenvaluesfromhours2and24wereaveragedtoassessbehaviorbeforeadditionalsnailswereaddedandhours26and48wereaveragedtoassessbehaviorafteradditionalsnailswereadded.Foreachsnail,theaveragesfromaftertheadditionofsnailsweresubtractedfromtheaveragesfrombeforethesnailswereaddedtodeterminehowthecumulativedistancemovedandthedistancetothenearestconspecificdifferedbetweenthefirstandsecond24hperiods.Thus,positivevaluesrepresentedgreaternetdistancetraveledandconspecificseparationbeforeadditionalsnailswereaddedthanafteradditionalsnailswereadded.Also,inthesecond24hperiod,foreach10sincrement,wesubtractedthedistancetothe

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nearestNZMS(intreatmentsthatincludedNZMS)fromthedistancetothenearestconspecificandcomputedanaverageforhours26and48.PositivevaluesrepresentsnailsbeingnearerNZMSthanaconspecificandnegativevaluesrepresentbeingnearertoaconspecific.

Therewerefourprimaryquestionsthatwewishedtoaddresswiththesedata;1)doestheadditionofNZMSreducethedistancenativesnailsmove,2)donativesnailstendtoreduceseparationamongconspecificsafterNZMSareadded,3)donativessnailstendtobeclosertoaconspecificthanNZMS,and4)donativesnailsspendmorecumulativetimeclosertoaconspecificthanaNZMS?Datafortwooftheresponsevariables,netdistancetraveledanddistancetonearestconspecificwereanalyzedasa3-wayANOVAwithinitialspecies,speciesaddedafter24hrs,andnumberofindividualsaddedasmaineffects.TheresponseofwhethersnailswereclosertoNZMSorconspecificswasanalyzedasatwo-wayANOVAwithspeciesduringtheinitial24hrsandthenumberofadditionalsnailsaddedasmaineffects.DatawereanalyzedwiththesoftwareprogramR(Hornik2016)andvalueswereconsideredsignificantatP<0.05.Significantmaineffectsandassociatedinteractionswerefurtherexploredusingcontrasts(Kuehl2000).Alog-linearanalysiswasperformedtodeterminewhethersnailsspentmorecumulativetimeneareraconspecificthanaNZMS.Forthisanalysis,theproportionoftensecondtimeincrementsduringhours26and48thateachindividualnativesnailwasclosertoaconspecificthantoaNZMSwasdeterminedandwedeterminedwhetherthecumulativetimethatsnailswereclosertoaconspecificvariedbetweenthetwonativespeciesandwiththenumberofNZMSadded.Theanalysiswasperformedusingthe"GLM"functioninprogramR(Hornik2016).

Results

Thenetdistancethesnailsmoveddidnotvarywithspeciesthatwasaddedafter24hrs(Figure1;F2,63=1.61,P=0.21),indicatingthatthemovementofnativesnailswasnotsignificantlyreducedwiththeadditionofNZMS.Also,thenetdistancethatthesnailsmoveddidnotvarywiththenumberofindividualsaddedafter24hrs(F2,63=1.38,P=0.26),indicatingthatthemovementofthesnailswasnotdensitydependant.Onaverage,P.kolobensismoved228±146mm/hr(mean±SD),A.limosusmoved275±128mm/hr,andNZMSmoved212±168mm/hr.

Theseparationamongconspecificsnailsafter24hrsvariedwiththespeciesofsnailadded(Figure2;F2,63=4.08,P=0.02)butdidnotvarywiththenumberofsnailsadded(F2,63=2.61,P=0.08).TheonlysignificantchangeinseparationoccurredamongP.kolobensis(Tukey'sHSDTest,P=0.02),wheredistancetothenearestconspecificdecreasedby15.8±10.3mmaftermoreconspecificswereadded.Forbothnativespecies,thedistancetothenearestconspecificdidnotchangeafterNZMSwereadded(bothP≥0.06).

NativesnailpreferenceforresidingnearertoaconspecificthanaNZMSvariedwiththenumberofNZMSadded(Figure3;F2,25=14.69,P<0.01)butdidnotvarybetweenthetwonativespecies(F1,25=0.62,P=0.44).ContrastsindicatedthatwhenoneNZMSisaddedthatsnailswereonaverage29.0±5.5mmclosertoaconspecificthanaNZMSthanwheneitherthreeorsixNZMSwereadded(t1,25=5.26,P<0.01).Incontrast,wheneitherthreeorsixNZMSwereadded,thenativesnailsshowednopreferencetowardsbeingneareraconspecificoraNZMS(t1,25=0.82,P=0.42).Regardlessofthedistance

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separatingnativesnailsandNZMS,bothnativespeciesspentmorecumulativetimeclosertoaconspecificthanaNZMSandthisvariedwiththenumberofNZMSadded(Table1;χ2,P<0.01,df=50).OddratiosshowedthatP.kolobensiswere1.4timesmorelikelythanA.limosustobeclosertoaconspecificthanaNZMSwhensixNZMSwasaddedtoatestarena.Thisoddsratiowas0.9whenoneNZMSwasaddedand1.1whenthreeNZMSwereadded.Mudamnicolawere0.8timesaslikelytobenearesttoaconspecificthanaNZMSwhenoneNZMSwasaddedand1.2and1.4timesmorelikelytobenearerotherA.limosusthanNZMSwheneitherthreeorsixNZMSwereadded,respectively.

Finally,thedistanceamongNZMSvariedwiththenumberofadditionalNZMSadded(Figure4;F2,26=32.6,P<0.01).TheresultsofaTukey'smultiplecomparisontestshowedthatthedistancetothenearestNZMSwassignificantlycloserwhensixNZMSwereaddedthanwhenthreewereaddedandtheadditionofthreeNZMSleadtosnailsbeingclosertooneanotherthanwhenasingleNZMSwasadded(Pforallpairwisecomparisons≤0.04).

Conclusions

Invasionsbyexoticspeciesarebecomingincreasinglycommonandmoreresearchontheinteractionsbetweennativeandnon-nativespeciesisrequired(Byers2000).WeobservedsnailsinourbehaviortrialtodeterminewhetherinterferenceoccursbetweenNZMSandP.kolobensisorA.limosus.TheresultsfromthesetrialsindicatethattheadditionofNZMSdidnotalterthewillingnessofthenativesnailspeciestomove.Thedistancesandhencevelocitiesofthenativesnailsdidnotvarybyspeciesadded,nordidthedistancemovedchangebetweenthefirstandsecond24hrobservationperiods.Also,thedistancetothenearestconspecificdidnotchangewhenNZMSwereadded,indicatingthatNZMSdidnothaveanantagonisticeffectonthenativesnails.BothP.kolobensisandNZMSmovedclosertooneanotherwhenconspecificswereadded,suggestingattractionamongindividualswithinthesespecies.BothA.limosusandP.kolobensiswereequidistantlyspacedbetweenconspecificsandNZMSwheneitherthreeorsixNZMSwereadded,whichagainindicatesalackofantagonisticeffect.Interestingly,however,spacingamongspecieswassimilarwheneitherthreeorsixNZMSwereadded,whichprovidessomeindicationthatthenativesnailssoughtcompanyofconspecificsathighNZMSdensities.ThisisfurthersupportedbydatashowingthatbothnativespeciesspentmorecumulativetimeneareraconspecificthanNZMSathigherNZMSdensitiesthanlowerNZMSdensities.OtherstudieshavedocumentedsimilaraggregationamongsnailsincludingAchatinafulica(Chaseetal.1980)andBiomphalariaglabrata(Simpsonetal.1973).

TheresultsfromourresearchindicatethatNZMSdidnotdirectlyaffectthebehaviorofP.kolobensisorA.limosus.TherearefewNZMSpredatorsandparasitesinNorthAmericaandNZMStolerateawiderangeofphysiochemicalconditions(AlonsoandCastro-Diez2008)andthusNZMSmayexertastrongercompetitiveeffectonP.kolobensisorA.limosusundercertainenvironmentalconditions.LittleisknownaboutP.kolobensisandA.limosus,buttherangeofthesespecieshasnotexpandedlikeNZMSanditislikelythatthesespeciesarelesstoleranttoextremeconditionsastheNZMS.Thus,humanalterationofecosystemsmaycreateconditionsthataremoreconduciveforNZMSandlessfavorableforP.kolobensisandA.limosus.Ingeneral,therearemanyhydrobiidspeciesintheIntermountainWest(HershlerandPonder1998)andmanyofthesespecieshaverestrictedranges.Due

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torelatedness,competitionbetweenNZMSandnativehydrobiidswouldbeexpectedbutlittleevidenceofcompetitionwasobservedinourstudies.FutureresearchshouldevaluatetheeffectofNZMSonadditionalspeciesandshouldfocusonNZMSeffectsinnaturalenvironments.

LiteratureCited

Aberle,N.,H.Hillebrand,J.Grey,andK.H.Wiltshire.2005.Selectivityandcompetitiveinteractions betweentwobenthicinvertebrategrazers(AsellusaquaticusandPotamopyrgusantipodarum): anexperimentalstudyusing13C-and15N-labelleddiatoms.FreshwaterBiology50:369–379.

Alonso,A,andP.Castro-Díez.2008.Whatexplainstheinvadingsuccessoftheaquaticmudsnail Potamopyrgusantipodarum(Hydrobiidae,Mollusca)?Hydrobiologia.614:107–116.

Byers,J.E.2000.Competitionbetweentwoestuarinesnails:implicationsforinvasionsofexoticspecies. Ecology.81:1225–1239.

Chase,R.,R.P.Croll,andL.L.Zeichner.1980.AggregationinsnailsAchatinafulica.Behavioraland NeuralBiology30:218-230.

Hershler,R.,andW.F.PonderWF.1998.Areviewofmorphologicalcharactersofhydrobioidsnails. SmithsonianContributionstoZoology600.

Hornik,K.2016.TheRFAQ.http://cran.r-project.org/doc/FAQ/R-FAQ.html.Accessed2-11-16.

Kerans,B.L.,M.FDybdahl,M.MGangloff,andJ.E.Jannot.2005.Potamopyrgusantipodarum: distribution,density,andeffectsonnativemacroinvertebrateassemblagesintheGreater YellowstoneEcosystem.JournaloftheNorthAmericanBenthologicalSociety24:123–138.

Kerans,B.L.,C.A.Cada,andJ.Zickovich.2010.AsymmetricalbehavioralinteractionsbetweentheNew Zealandmudsnail,Potamopyrgusantipodarum,andscraping,collector-gatheringandcollector- filteringmacroinvertebrates.JournalofFreshwaterEcology25:657–666.

Krist,A.,andM.Dybdahl.2005.TheinvasiveNewZealandmudsnail,Potamopyrgusantipodarum, reducesgrowthofthenativesnail,Fossariasp.UniversityofWyomingNationalParkService ResearchCenterAnnualReport29:42–48.

Kuehl,R.O.2000.DesignofExperiments:StatisticalPrinciplesofResearchDesignandAnalysis,2nd Edition.DuxburyPress,PacificGrove,California.

Moore,J.W.,D.B.Herbst,W.B.Heady,andS.M.Carlson.2012.Streamcommunityandecosystem responsestotheboomandbustofaninvadingsnail.BiologicalInvasions14:2435–2446.

Myrick,C.A.2009.Alow-costsystemforcapturingandanalyzingthemotionofaquaticorganisms. JournaloftheNorthAmericanBenthologicalSociety28:101–109.

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Richards,D.C.2004.CompetitionbetweenthethreatenedBlissRapidssnailTaylorconchaserpenticola (Hershleretal.)andtheinvasiveaquaticsnailPotamopyrgusantipodarum(Gray).Dissertation, MontanaStateUniversity.

Riley,L.A.,andM.F.Dybdahl.2015.Therolesofresourceavailabilityandcompetitioninmediating growthratesofinvasiveandnativefreshwatersnails.FreshwaterBiology60:1308–1315.

Riley,L.A.,M.F.Dybdahl,andR.O.Hall.2008.Invasivespeciesimpact:asymmetricinteractions betweeninvasiveandendemicfreshwatersnails.JournaloftheNorthAmericanBenthological Society27:509–520.

Simpson,A.W.,J.D.Thomas,C.R.Townsend.1973.Socialbehaviorinthefreshwaterpulmonatesnail Biomphalariaglabrata(Say).BehavioralBiology9:731-740.

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Table1:PercentageofobservationswhereP.kolobensisandA.limosuswereclosertoaconspecificthantoNZMS.Thepercentageofobservationsandstandarddeviation(SD;inparentheses)arebasedon5replicatesofeachtreatmentand720observationsperreplicate(120minobservationx6observationperiods/min).

NativeSpecies

Numberof

NZMSin

Arena

%ofObservationsClosertoConspecific

ToquervilleSpringsnail 1 45.6(5.6)

3 57.6(23.4)

6 72.6(4.7)

MudAmnicola 1 37.3(9.3)

3 61.0(9.8)

6 70.9(13.7)

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Species

Toquerville Mud Amnicola NZMS

Diff

eren

ce In

Net

Mov

emen

t Bef

ore/

A

fter S

nail

Addi

tion

(mm

)

-200

-150

-100

-50

0

50

100

150Conspecific AddedNZMS Added

Figure1:DifferenceinmovementofP.kolobensisandA.limosusaftertheadditionofconspecificscomparedtotheadditionofNZMS.Dataonthey-axisrepresenttheaveragenetdistancethatsnailsmovedafteradditionalsnailswereaddedsubtractedfromtheaveragenetdistancemovedbeforeadditionalsnailswereadded.Positivevaluesrepresentgreaterdistancestraveledbeforeadditionalsnailswereadded.Errorbarsrepresent±1SD.

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Time (hrs)

24 48

Mea

n Se

para

tion

Amon

g

Con

spec

ifics

(mm

)

20

30

40

50

60

70

80

90Toquerville-Toquerville AddedToquerville-NZMS AddedMud Amnicola-Mud Amnicola AddedMud Amnicola-NZMS Added

Figure2:AveragedistancebetweenP.kolobensisorA.limosuseitheraftertheadditionofconspecificsortheadditionofNZMS.CirclesrepresentdatafromP.kolobensisandtrianglesrepresentA.limosus.ClosedsymbolsrepresenttheadditionofconspecificsandopensymbolsrepresenttheadditionofNZMS.Errorbarsrepresent±1SD.

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Species

Toquerville Mud Amnicola-40

-20

0

20

40

601 NZMS Added3 NZMS Added6 NZMS Added

Diff

eren

ce In

Sep

arat

ion

Betw

een

C

onsp

ecifi

c an

d N

ZMS

(mm

)

Figure3:AveragedifferenceindistancebetweennearestconspecificandnearestNZMSaftertheadditionofNZMSatthreedifferentdensities.Dataonthey-axisrepresenttheaveragedistancetothenearestconspecificminustheaveragedistancetothenearestNZMS.PositivevaluesrepresentsnailsbeingnearertoconspecificsandnegativevaluesrepresentsnailsbeingclosertoNZMS.Errorbarsrepresent±1SD.

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# of NZMS Added

1 3 6

Dis

tanc

e to

Nea

rest

NZM

S (m

m)

0

20

40

60

80

100

A

B

C

Figure4:AveragedistanceofNZMStothenearestNZMSaftertheadditionofeither1,3,or6NZMStothetestarenas.TreatmentswithdifferentlettersabovethebarsaresignificantlydifferentfromoneanotheratP<0.05.Errorbarsrepresent±1SD.

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Task2:EffectoftheInvasiveNewZealandMudsnailontheRecruitmentandSurvivalofTwoNativeSnails

Background

NewZealandmudsnails(NZMS)Potamopyrgusantipodarumareanexampleofasuccessfulinvasivespecies(AlonsoandCastro-Diez2008).Onceestablished,NZMScanbecomeadominantcomponentofaninvertebratecommunityandconsequently,NZMShavetheabilitytonegativelyaffectothertaxa.Forexample,severalstudieshavefoundthatthegrowthratesofothersnailtaxaaresuppressedinthepresenceofNZMS(KristandDybdahl2005;RileyandDybdahl2015).Rileyetal.(2008)foundthatNZMSlimitedthegrowthofthenativesnailPyrgulopsisrobustaandthatthenativesnailfacilitatedthegrowthofNZMS.StudieshavealsofoundtheabundanceofotherinvertebratetaxatocovarywithNZMSabundance(Keransetal.2005;Mooreetal.2012).Finally,NZMShavebeenshowntoalterthebehaviorofotherspecies.Forexample,Keransetal.(2005)foundthatotherspeciesofmacroinvertebrateswerelessabundantontilesthatwereheavilycolonizedbyNZMS.Keransetal.(2010)foundthatNZMSinterferedwiththeforagingofmayfliesinthefamilyBaetidaebutthatthecaddisflyBrachycentrusoccidentaliscausedNZMStoabandonthesurfacesoftiles.ThepresenceofNZMShasalsobeenassociatedwithshiftsinfeedingpreferencesintheisopodAsellusaquaticus(Aberleetal.2005)andbaetidmayflies(Keransetal.2010).

NewZealandmudsnailsaremembersofthesnailfamilyHydrobiidae,whichisthelargestfreshwatermolluskgroupwithmorethan1,000species(HershlerandPonder1998).Manyspecieswithinthefamilyhavespecifichabitatrequirements,limitedranges,andaresensitivetohabitatalteration(HershlerandPonder1998).Consequently,manyhydrobiidspeciesareconsideredthreatenedorendangered(e.g.,BlissRapidssnailTaylorconchaserpenticola;Richards2004).TheeffectsthatNZMShaveonotherhydrobiidtaxaarepoorlyunderstoodbutsimilaritiesinbodysize,habitat,andlife-historyrequirementswouldsuggestthatNZMScouldhavestrongercompetitiveeffectsonotherhydrobiidspeciesthanotherinvertebratetaxa.

ThegoalsofourresearchweretoassesshowNZMSaffectthebehavioroftwootherhydrobiidspecies,theToquervillespringsnailPyrgulopsiskolobensisandmudamnicolaAmnicolalimosus,bothofwhicharenativetotheUnitedStates.TodothisweplacedP.kolobensisorA.limosusinexperimentalmesocosmswithvaryingdensitiesofNZMSanddeterminedhowNZMSaffectedthesurvivalandrecruitmentofthenativesnails.WehypothesizedthatNZMSwouldreducethesurvivalandrecruitmentofthetwonativespecies.

Methods

SnailCollectionandMaintenance

Pyrgulopsiskolobensis,A.limosus,andNZMSwerecollectedinthefieldandtransportedtotheUtahDivisionofWildlifeResource'sFisheriesExperimentStation(FES;CacheCounty,Utah).Snailsweretransportedin4.0Lvolumeplasticbagsthatwerefilledwith1-2Lofwaterandnaturalvegetationfrom

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thecollectionsites.Bagswerefilledwithoxygenandtransportedincoolerswithice.P.kolobensiswerecollectedonJuly28,2015fromasmallspringsituatedonNationalForestlandnearPineValley,Utah(WashingtonCounty).MudamnicolawerecollectedonAugust3,2015fromtheRightHandForkoftheLoganRiver(CacheCounty,Utah).NZMSwerecollectedonJuly27,2015fromtheLoaStateFishHatchery(WayneCounty,Utah).UponarrivaltoFES,snails,water,andcollectionsitevegetationweretransferredtoplasticaquaria(35x21x12.5cm,lengthxwidthxheight)withoneaquariumusedperspecies.Anairstoneconnectedtoanaquariumairpumpwasusedtoaeratetheaquariaandwerestoredinarefrigerator(FrigidaireElectroluxFFHT2021QW10,Charlotte,NorthCarolina,USA)withaon/offcyclecontrolledbyatemperaturecontrolswitch(JohnsonControlsmodelA419ABG-3,WestValleyCity,Utah,USA).Thetemperatureintherefrigeratorwassetat6°Candaveraged5.2±2.3°C(mean±SD;measuredevery15minwithaHoboOnsettemperaturelogger,Bourne,Massachusetts,USA).WaterexchangeswereperformedtwiceweeklyusingFESwellwater(pH=7.2,hardnessandalkalinity=200mg/L).Toprovidefood,watercressNasturtiumofficinalewasperiodicallycollectedfrombelowtheFESfishhatchery,rinsed4-5xwithwatertoremoveotherinvertebrates,andaddedtotheaquaria.

ExperimentalDesign

TheeffectofNZMSonthesurvivalandrecruitmentofA.limosusandP.kolobensiswasdeterminedusingsevendifferenttreatmentswithfivereplicatesofeachtreatment.Theseventreatmentsincludedtenindividualsfromeachspecies(NZMS,A.limosus,andP.kolobensis)housedallopatrically,fiveindividualsfromthetwonativespeciesheldsympatricallywithfiveNZMS,andfiveindividualsfromthetwonativespeciesheldsympatricallyalongwithtenNZMS.Snailswereaddedtoplasticaquaria(35x21x12.5cm,lengthxwidthxheight;136snails/m2intreatmentswith10snailsand204snails/m2intreatmentswith15snails)onDecember9,2015andlasted60d.Theaquariawereplacedontwoadjacentstorageshelvingunits,eachwiththreeshelves.Wewereconcernedabouttemperaturedifferencesamongshelvesandstratifiedtheexperimentbyplacingonereplicateofeachtreatmentoneachshelf(oneshelfononestorageunitnotused).Treatmentplacementonindividualshelveswasrandomized.TemperaturedatacollectedwithHoboOnsettemperatureloggers(Bourne,Massachusetts)revealedthattreatmentstratificationwasjustifiedasthereweresignificanttemperaturedifferencesamongshelves(F2,17379=6738,P<0.01,topshelves:13.9±2.9°C,middleshelves:12.4±2.3°C,bottomshelves:8.6±2.4°C,allmean±SD).Toprovideforage,10.0gofwatercresswasaddedtoeachtoteandwasreplenishedbyadding5.0additionalgramshalf-waythroughtheexperiment.Thewaterineachtotewasreplacedevery3-4dbypouringthecontentsofthetotethrougha100µmsieveandaddingthecontentsandfreshFESwellwaterbacktotheaquaria.Aerationwasprovidedtoeachtoteviaanaquariumairpumpandairstone.

Attheendofthetrial,adultsnailswereremovedfromtheaquariaandsurvivaloftheseadultsnailswasassessedviaobservationunderadissectingmicroscopeandsnailsthatreactedtotouchwithaneedlewereconsideredalive.Snailsthatdidnotrespondorhademptyshellswereconsidereddead(Schisleretal.2008).Theremainingaquariacontentswerefrozenandlaterthawedandnumbersofjuvenilesfromeachspeciesweredeterminedusingadissectingmicroscopeunder15Xmagnification.Thesurvivalstatusofthejuvenilesattheendofthetrialwasnotassessed.Tofacilitateinseparating

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juvenilesfromdetritus,sampleswerestainedusinga0.1%AlizarinRedsolutionfor2hrsfollowedbyrinsingwithdeionizedwater(HowardandSmith1983).Sampleswerethenstainedfor10-15susing1.0%LightGreenSFYellowishfollowedbyadditionalrinsing(HowardandSmith1983).

Data(survivalofadultsfromeachspeciesandnumbersofjuvenilesproducedforeachspecies)wereanalyzedusingone-wayrandomizedcompleteblockdesign(Kuehl2000).Themaineffectwastreatmentandeachshelfwasconsideredablock.ContrastswereusedtodetermineNZMSeffectsbycomparingcontrolconditions(speciesheldallopatric)againstthetwoNZMSdensitytreatments.Similarly,contrastswereusedtocomparesurvivalandjuvenileproductionbetweenthetwoNZMSdensities.AllanalyseswereperformedusingprogramR(Hornik2016)andvalueswereconsideredsignificantatP<0.05.

Results

Thesurvivaloftheadultsnailsdidnotvaryamongtreatments(F6,24=1.97,P=0.11)indicatingthatNZMSpresenceanddensitydidnotaffectthesurvivalofthenativesnails.ThesurvivalofNZMSdidnotvarybetweenthetwodensities(5versus10NZMSwithinaquaria;F3,12=2.65,P=0.10).Thenumbersofjuvenilesnailsproducedvariedamongtreatments(Table2;F6,24=4.67,P<0.01).Whenheldallopatrically,NZMSproductionexceededproductionofbothA.limosusandP.kolobensis(bothP<0.01).NoreductioninjuvenileproductionwasobservedwhenNZMSwereadded,regardlessofNZMSdensity(allP≥0.15).Significantdifferencesinjuvenileproductionwerealsoobservedafterstandardizationtocontrolfordifferencesinnumbersofadultnativesnailsamongtreatments(i.e.,numberofjuvenilesproduced/numberofadultsaddedtoaquaria;F6,24=3.45,P=0.01).Whenanalyzedinthismanner,underallopatricsituations,NZMSproducedmorejuveniles/adultthanbothA.limosusorP.kolobensis(bothP≤0.01)andtherewasnodifferenceinjuvenileproductionamongthetwonativespecies(t1,24=1.22,P=0.23).Undersympatricconditions,theadditionofNZMShadnoeffectontheproductionofP.kolobensis(t1,24=0.29,P=0.77)whereastheadditionofNZMSincreasedjuvenileproductionamongA.limosus(t1,24=2.15,P=0.04).Regardless,chi-squaretestsshowedthattheproductionofjuvenileswasnotdisproportionatelyskewedtowardsNZMS(allP≥0.10).

Conclusions

TheresultsindicatethatthepresenceofNZMSdidnotaffectthesurvivalorrecruitmentofthenativesnails.Weobserved,however,thatNZMSrecruitmentrates(juvenilesproduced/adult)werehigherthanthenativespecies.Otherstudies(e.g.,AlonsoandCastro-Diez2008)havealsonotedahighreproductiverateamongNZMS.ThereproductiverateforNZMSinourstudy(0.02±0.01individuals/d)wasmuchlowerthanhasbeenreportedinotherstudies(0.1-1.3individuals/d;Halletal.2006).ItispossiblethatreproductiveratesinNZMSarereducedwhensnailsareremovedfromnaturalconditions,butregardless,weingeneralhaveseenlessreproductionamongNZMScollectedfromtheLoaHatcherythanhasbeenreportedbyotherresearchers(Oplinger,personalobservation).ItappearsthatthecombinationofhighfecundityandgrazingsuccesscontributestotheeffectthatNZMShaveonothertaxa.Forexample,Mooreetal.(2012)foundthattheabundanceofnativegrazersdeclinedasNZMSnumbersincreasedandthenrecoveredwhentheNZMSpopulationcrashed.Rileyetal.(2008)andRiley

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andDybdahl(2015)studiedNZMSinteractionswithPyrgulopsisrobusta,whichisinthesamegenusastheP.kolobensisandfoundasymmetriccompetitiveinteractions;thepresenceofNZMSaffectedP.robustabutP.robustadidnotaffectNZMS.TheeffectsofNZMSwereassessedinthesestudiesintermsofgrowthandalthoughnotassessedinourstudy,changesingrowthmayultimatelyaffectrecruitmentandshouldbeevaluatedinP.kolobensisandA.limosus.

LiteratureCited

AberleN,HillebrandH,GreyJ,WiltshireKH.2005.Selectivityandcompetitiveinteractions betweentwobenthicinvertebrategrazers(AsellusaquaticusandPotamopyrgusantipodarum): anexperimentalstudyusing13C-and15N-labelleddiatoms.FreshwaterBiol.50:369–379.

AlonsoA,Castro-DíezP.2008.Whatexplainstheinvadingsuccessoftheaquaticmudsnail Potamopyrgusantipodarum(Hydrobiidae,Mollusca)?Hydrobiologia.614:107–116.

HallRO,DybdahlMF,VanderloopMC.2006.Extremelyhighsecondaryproductionofintroducedsnails inrivers.EcolAppl.16:1121-1131.

HershlerR,PonderWF.1998.Areviewofmorphologicalcharactersofhydrobioidsnails.SmCZool. 600.

HornikK.2016.TheRFAQ.http://cran.r-project.org/doc/FAQ/R-FAQ.html.Accessed2-11-16.

KeransBL,DybdahlMF,GangloffMM,JannotJE.2005.Potamopyrgusantipodarum:distribution, density,andeffectsonnativemacroinvertebrateassemblagesintheGreaterYellowstone Ecosystem.JNAmBentholSoc.24:123–138.

KeransBL,CadaCA,ZickovichJ.2010.AsymmetricalbehavioralinteractionsbetweentheNewZealand mudsnail,Potamopyrgusantipodarum,andscraping,collector-gatheringandcollector-filtering macroinvertebrates.JFreshwaterEcol.25:657–666.

KristA,DybdahlM.2005.TheinvasiveNewZealandmudsnail,Potamopyrgusantipodarum,reduces growthofthenativesnail,Fossariasp.UnivWyomingNat.ParkServ.ResearchCenterAnnual Report29:42–48.

KuehlRO.2000.DesignofExperiments:StatisticalPrinciplesofResearchDesignandAnalysis,2nd Edition.DuxburyPress,PacificGrove,California.

RichardsDC.2004.CompetitionbetweenthethreatenedBlissRapidssnailTaylorconchaserpenticola (Hershleretal.)andtheinvasiveaquaticsnailPotamopyrgusantipodarum(Gray).Dissertation, MontanaStateUniversity.

RileyLA,DybdahlMF.2015.Therolesofresourceavailabilityandcompetitioninmediating growth ratesofinvasiveandnativefreshwatersnails.FreshwaterBiol.60:1308–1315.

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RileyLA,DybdahlMF,HallRO.2008.Invasivespeciesimpact:asymmetricinteractionsbetweeninvasive andendemicfreshwatersnails.JNAmBentholSoc.27:509–520.

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Table2:Averagenumber(withSDinparentheses)ofnativesnailandNZMSrecruitsproducedperadultaddedintoaquaria.MArepresentsmudamnicolaandToqrepresentsToquervillespringsnail.

Treatment #ofNatives #ofNZMS

10MA 0.08(0.1)

10Toq 0.2(0.2)

10NZMS

1.0(0.6)

5MA+5NZMS 0.3(0.4) 0.5(0.4)

5MA+10NZMS 0.5(0.5) 1.2(0.5)

5Toq+5NZMS 0.1(0.2) 0.5(0.4)

5Toq+10NZMS 0.4(0.3) 0.6(0.1)

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Task3:RecruitmentPotentialAmongNewZealandMudSnailsthatSurviveFishDigestion

Background

NewZealandmudsnails(NZMS;Potamopyrgusantipodarum)havebeendiscoveredinmanypublicandprivatefishhatcheries.WithinUtah,theNZMSisfoundwithintheLoaStateFishHatcheryandhasbeenknowntooccurwithinthehatcherysinceNovember2007.NZMSappeartohavenoadverseeffectsonfishwithinhatcheries.ThepresenceofNZMShasbeenassociatedwithdecreasesingrowthandconditionofwildfish(VinsonandBaker2008).

HatcheryrearedfishcanbedistributedtomanywatersandthereareconcernsinhatcheriesthathaveNZMSthatsnailscanbeinadvertentlystockedatthesametimethatfisharestocked.Therearemanystepsthatcanbetakentodecreasethisrisk.Forexample,hatcherydistributiontruckscanbefilledwithfilteredwaterorwaterfromaNZMS-freesourceandthelikelihoodofaccidentallyloadingsnailsintothedistributiontruckcanbedecreasedbynottouchingtheracewaywallsandfloorwithanetwhileloadingfish.Onelargerconcern,however,isthatthefishthemselvescouldhaveNZMSintheirdigestivetractsandthatthesnailscouldbeexcretedaliveafterstocking.Oplingeretal.(2009)foundthat4.5%ofNZMSthatareingestedbysub-catchablesizedrainbowtroutsurvivedigestion.StaffattheLoaHatcherydissected1,539fishinracewaysandfoundatotalof120NZMSinthedigestivetractsofthesefish(Oplingeretal.2011).BasedontheseaveragesitisestimatedthatoneliveNZMScouldbeinadvertentlyaddedtothewildforevery285fishstockedfromthehatchery.Thehatcheryhasapolicystatingthatfisharequarantinedpriortostocking.Atotalof2,100fishinspeciallycleanedquarantineracewaysweredissectedandnoNZMSwerefoundinthedigestivetractsofthesefish(Oplingeretal.2011).Thisdataindicatesthatinprinciplethatthereisnoriskassociatedwiththestockingoffishfromthequarantineraceways.Inreality,however,NZMSareknowntooccurineveryracewayatthefacilityanditislikelythatsomeNZMSarenotkilledduringthepreparationofthequarantineraceways.ThusthereissomeriskthatthestockingoffishfromtheseracewayscouldleadtotheestablishmentofnewNZMSpopulations,albeitthequarantineprocessgreatlyreducesthisrisk.Regardless,eventhoughitisknownthat4.5%ofingestedNZMSsurvivedigestion,itisnotknownwhethersnailsthatpassthroughthedigestivetractofafishmakeafullrecoveryandeventuallyreproduceorifthesesnailsaresocompromisedbythedigestionprocessthattheyneverreproduceorultimatelypassaway.ThisdetailisimportantbecauseNZMSreproduceasexuallyandtheintroductionofasinglesnailmaybesufficienttoleadtotheestablishmentofanewNZMSpopulation.

ThepurposeofthisstudywastodeterminewhetherNZMSthatsurvivedigestionarecapableofreproducing.WecomparedthereproductionabilityofsnailsthatweredigestedbytwosizeclassesofrainbowtroutOncorhynchusmykiss.Thiswasdonetodeterminewhetherthe"thoroughness"ofdigestionvarieswithfishsize.

Methods

ThisstudywasperformedattheLoaStateFishHatchery.Sixaquaria,each110Linvolumewereplacedonracewayfloors.Asiphonwasusedtodeliverwaterintotheaquariaandoutflowwas

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directedthroughastandpipe.Boardswereplacedontopoftheaquariatopreventfishescape.Threeaquariawereusedforeachfishsizeclasswith7-8fishplacedintoeachaquaria.FishwereacquiredfromtheEganandGlenwoodStateFishHatcheries.Fishinthesmallersizeclassrangedbetween122and159mmtotallengthwithanaverageof141mm.Fishinthelargersizeclassrangedbetween160and240mmtotallengthwithanaverageof207mm.Wehadhopedtohaveagreaterdiscrepancyinlengthbetweenthelargerandsmallerfish.Thesmallerfishareofasizeconsistentwith"sub-catchables"thatarestockedwithinUtah.Wehopedtofind"catchable"fishbutthelargersizeclasswerethelargestfishavailableatthetimeofthestudy.

WefoundthatthefishdidnotvolitionallyconsumeNZMS.Instead,NZMSwereforce-fedtothefishbyanesthetizingthefishwithMS-222andinsertingatubeintotheirstomachs(Oplingeretal.2009).TenNZMSwereplacedintothetubeandasyringefilledwithwaterwasusedtoflushthesnailsfromthetubeintothestomachs.Thefishwereheldfor15minutesinfreshwatertoallowforanesthesiarecoveryandtoprovidethefishtheopportunitytoregurgitatesnails.Afterwards,thefishwereplacedbackintotheaquaria.

Twicedaily,thebottomsoftheaquariaweresiphonedandwastewasremoved.NZMSwereseparatedfromtheotherwasteandplacedintobeakersofhatcherywater.Snailswereprovidedatleast6hourstorecoverandafterrecovery,snailsthatmovedwereconsideredalive.Livesnailswereseparatedfromdeadsnailsandwereplacedinto5.7LaquariathatwereplacedontheflooroftheLoaHatcheryShop.Asinglelivesnailwasaddedtoeachaquariaand10gofwatercressNasturtiumofficinalewasaddedtoprovidethesnailswithforage.Atotalof66aquariawereestablished;22containedsnailsthatsurviveddigestionbysmallerfish,22containedsnailsthatsurviveddigestionbylargerfish,and22containedsnailsthatwerenotfedtofishandwerethuscontrols.Thesnailsremainedintheaquariafor74d.Thewaterandwatercressineachaquariawasreplacedthreetimesduringtheholdingperiod.Aftertheholdingperiodwascomplete,thesurvivalofthesnailswasassessedandthecontentsofeachaquariawerepreservedbyfreezing.

SamplesweretransportedtotheFisheriesExperimentStationwheretheywerethawedandfilteredusingsievestocollectparticlesthatwere100-500µminsize.Theseparticleswerestainedfor1-4hrsina0.1%alizarinredsolution(HowardandSmith1983).Theseparticleswerethenrinsedandcounterstainedfor10susing1.0%lightgreen,SFyellowish+1%glacialaceticacidandafterwardstheparticleswerethoroughlyrinsed(HowardandSmith1983).Adissectingmicroscopewasusedtoscanalloftheparticlesunder20xmagnificationandNZMSneonateswereobservedandenumerated.Notall66sampleswereprocessed.Weenumeratedneonatesfrom11ofthe22snailsthatsurviveddigestionbythesmallerrainbowtrout,7ofthe22snailsthatsurviveddigestionbythelargerrainbowtrout,and5ofthe22controlsamples.Anone-wayANOVAwasusedtocompareneonatenumbersacrosstreatments.Inaddition,at-testwasusedtodeterminewhetherthenumberofneonatesobservedwasgreateramongsnailsthatsurvivedtheentire74dholdingperiod.AlldatawereanalyzedusingR(Hornik2016)andconsideredstatisticallysignificantatP<0.05.Logarithmictransformationswereusedtoensurethedatametthenormalityassumptionoftheanalyses.

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Results/Discussion

Neonateswerefoundinalltreatments(Figure5)andthenumberofneonatesproduceddidnotvaryamongtreatments(F2,20=0.48,P=0.63).Only5ofthe66snails(7.6%)ofthesnailssurvivedtheentire74dholdingperiod.Twoofthosesnailswerefromthecontroltreatment,twosurviveddigestionbysmallerfish,andonesurviveddigestionbylargerfish.Thenumberofneonatesproduceddidnotvaryamongaquariawherethesnailssurvivedtheentire74dholdingperiodcomparedtoaquariawherethesnailsdidnotsurvivetheentireholdingperiod(Figure6;F1,21=0.89,P=0.36;3of23samplesprocessedhadNZMSthatsurvivedthe74dholdingperiod).ThesedataclearlyindicatethatNZMSthatsurvivedigestionhavetheabilitytoreproduce.Thus,iffisharestockedfromahatcherythathasNZMS,anysnailsthatsurvivedigestionhavetheabilitytoreproduceandestablishnewNZMSpopulations.Also,reproductiveratesamongsnailsthatsurviveddigestionwerenotreducedcomparedtocontrols,indicatingthesurvivingsnailswereingoodcondition.Finally,similarnumbersofneonateswereproducedbysnailsthatsurvivedtheentire74dholdingperiodcomparedtosnailsthatdidnotsurvive.Thiswouldsuggestthatmostneonateswereproducedearlyintheholdingperiod,beforesignificantnumbersofsnailsdied.

Fish Size

Small Large Control

Neo

nate

s Pr

oduc

ed

0

1

2

3

4

5

6

7

8

9

Figure5:Averagenumberofneonatesproducedbysnailsthatsurviveddigestionbyeithersmallerorlargerrainbowtrout.Thecontroltreatmentreferstosnailsthatwerenotfedtofish.Errorbarsrepresent±1standarddeviationofthemean.

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Survival at Trial End

Dead Alive

Neo

nate

s Pr

oduc

ed

0

1

2

3

4

5

6

7

8

9

Figure6:Averagenumberofneonatesproducedbysnailswereeitheraliveordead74daysafterdigestionbyfish.Errorbarsrepresent±1standarddeviationofthemean.

LiteratureCited

Howard,D.W.,andC.S.Smith.1983.Histologicaltechniquesformarinebivalvemollusks.NOAA TechnicalMemorandumNMFS-F/NEC-25.

Oplinger,R.,W.,P.Brown,andE.J.Wagner.2009.Effectofsodiumchloride,tricaine methanesulfonate,andlightonNewZealandmudsnailbehavior,survivalofsnailsdefecated fromrainbowtrout,andeffectsofepsomsaltonsnaileliminationrate.NorthAmericanJournal ofAquaculture71:157-164.

Oplinger,R.,P.Brown,E.Wagner,M.Durfey,E.VanDyke,andT.Howick.2011.Researchandefforts placedintoremovingNewZealandMudSnailsfromtheLoaStateFishHatchery.UtahDivision ofWildlifeResourcesPublication11-25.

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Vinson,M.,andM.Baker.2008.PoorgrowthofrainbowtroutfedNewZealandMudSnails Potamopyrgusantipodarum.NorthAmericanJournalofFisheriesManagement28:701–709.

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Task4:UpdateoftheRangeofNZMSwithinUtah

NewZealandmudsnails(NZMS)werediscoveredintheLoaStateFishHatcheryin2007.Aftertheirformaldiscovery,NZMSshellswerefoundinpilesoffishwasteatthehatcheryandthesepileswereproducedpriorto2007(likely2004or2005).Thus,itisassumedthatNZMSactuallyenteredthehatcheryearlierthan2007.ThediscoveryofNZMSin2007promptedaquarantineoftheLoaHatcheryandsubsequentsamplingfoundnoNZMSinanywatersthatwerestockedbyLoain2007.Sitesamplingwasperformedbyspendingoneman-houroftimeassessingthepresence/absenceofNZMSinhabitatsthataresuspectedtoharborNZMS.

InlightofthefactthatNZMSwerelikelyintroducedintoLoapriorto2007,wereviewedstockingrecordsandidentified22sites(Table3)thatwerestockedbyLoabetween2004and2006thathadnotpreviouslybeensurveyedforNZMS.Thegoalistovisit3-5ofthesesitesperyearuntilallsitesaresampled.In2015,WideHollowReservoir,UpperandLowerBoxCreekReservoirs,andPoseyLakeweresurveyedforNZMS.NoNZMSwerefoundatanyofthesesites.AnupdatedmapshowingthedistributionofNZMSwithinUtahispresentedinFigure7.Todate,noNZMShavebeenfoundatanysitesthatwereformerlystockedbyLoa.SamplingfromadditionalsitesinTable3willbeperformedacrossthenextseveralyears.

Table3:ListofwaterbodiesstockedbytheLoaStateFishHatcherythathadnotpreviouslybeenassessedforthepresenceofNZMS.

WaterBodyYearnsReservoir NavajoLake

BurrastonPonds EnterpriseReservoir,LowerTowneReservoir EnterpriseReservoir,UpperPoseyLake WideHollowReservoirGrantsvilleReservoir PalisadeReservoirGatesLake BoxCreekReservoir,LowerBeaverRiver BoxCreekReservoir,UpperNineMileReservoir AsayCreekColemanReservoir PanguitchLakeSettlementCanyonReservoir SevierRiver,EastForkMinersvilleReservoir MammothCreek

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Figure7:MapofthedistributionofNZMSwithinUtah.X'srepresentsitescontainingNZMSandO'srepresentsiteslackingNZMS.