AssessingnaturalresourcesintheNoosaBiospheretorestoreafunctionalestuary:
interimreport
Reportpreparedby:
DrCarmelMcDougall
AustralianRiversInstitute,GriffithUniversity,Brisbane
DrSimonWalkerEcologicalServiceProfessionalsPtyLtd,Brisbane
For:
TheNoosaBiosphereReserveFoundation
EcologicalServiceProfessionalsPtyLtd
October2020
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Authorcontactdetails'0449218134
8https://www.griffith.edu.au/australian-rivers-institute
ReportcitationMcDougallC,WalkerS,2020.AssessingnaturalresourcesintheNoosaBiospheretorestoreafunctionalestuary;interimreport.AustralianRiversInstitute,GriffithUniversity,Brisbane
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Contents1. ExecutiveSummary........................................................................................................42. ProjectBackground........................................................................................................53. Methods.........................................................................................................................7
Ambientwaterquality.............................................................................................7Aim1-EvaluatethedistributionanddiversityofoysterspecieswithintheNoosaestuary.....................................................................................................................7Aim2-Evaluatethesettlementpreferencesofdetectedoysterspecies...............9Aim3-InvestigatetheutilityofeDNAfordetectionandmonitoringofoysterbiodiversity.............................................................................................................10
4. ResultsandDiscussion.................................................................................................10Characterisationofcollectionsites........................................................................10ThedistributionanddiversityofoysterspecieswithintheNoosaestuary...........11SettlementpreferencesofoysterspeciesintheNoosaestuary...........................14Comparisonofmethodsforspeciesdetection......................................................18Historicalsignificanceandimplicationsforshellfishdesign..................................18
5. Acknowledgements.....................................................................................................196. References...................................................................................................................20
Figures
Figure1. Intertidalremnantoysterreef,TurkeyBeach,Queensland.............................5Figure2. SitesinthelowerNoosaEstuary.Bluedots:adultoystercollectionsite.Black
dots:settlementrackdeploymentsite.Pinkdots:eDNAsamplecollectionsite...........................................................................................................................8
Figure3. Settlementplaterackdesign.Top:constructionofsettlementracks.Bottom:settlementrackinsituatsiteSD1....................................................................9
Figure4. MorphologyofadultSaccostreaglomerataandSaccostrealineageG..........12Figure5. SubtidalrockrubbleandoysterbankatTewantin.........................................13Figure6. LowreliefaggregationofsubtidalleafoysterbedoversandandmudinWeyba
Creek...............................................................................................................13Figure7. Morphologyofspatofeachdetectedspecies................................................15Figure8. Averageabundance(±SE)ofrockoystersonhorizontalsettlementplates
amongsites.....................................................................................................16Figure9. Averageabundance(±SE)ofrockoystersonverticalsettlementplatesamong
sites.................................................................................................................16Figure10. Settlmentplateswithhighcoverageofsedimentonuppersurface..............17
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TablesTable1 Waterqualityparametersmeasuredinsituateachsite...............................11Table2 Temperatureandsalinityforoptimumgrowthandtolerancelimitfor
Saccostreaglomerata.....................................................................................13Table3 PERMANOVAresultsfordifferencesinoysterdensityamongsite,substrate
typesandsurfaceorientations........................................................................17
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1. ExecutiveSummary
Shellfishreefsareculturally,economically,andecologicallyimportantbuthavealmostentirelydisappearedfromAustralia’scoastlines.IntheNoosaestuary,oysterswereonceabundantbuthavenotrecoveredsinceoverharvestinginthelate19thcentury.Oysterreefrestorationprojectshavecommencedbuttheirefficacytorestorethislosthabitattypeisunknown.Thisprojectaimsto1)evaluatethedistributionanddiversityofoysterspecieswithintheestuary,2)evaluateoystersettlementpreferences,and3)investigateenvironmentalDNAtechniquesfordetectionandmonitoringofrestoredreefs.Thiswilldirectlyinformthedesignofreefmodulestomaximisesettlementofoysterspeciesforongoingrestorationprojets.
Thesudyfindsthat:
1. Minimally, there are four species of rock oyster present in the estuary. These includeSaccostreaglomerata(theSydneyrockoyster),SaccostrealineageB,SaccostrealineageG,andOstreaequestris.
2. Theoysters(andtheirspat)cannotbereliablyidentifiedbymorphologyalone.3. Ostreaequestriswasonlydetectedonsettlementplates,whereasSaccostrea lineageB
wasonlydetectedviasurvey.4. Oyster diversity appears to be higher near the rivermouth than in the upper reaches,
withSaccostreaglomerata thesolespeciespresentupstream.This result ispreliminaryandneedstobeverifiedwithsequencingofadditionalspecimens.
5. Several other native shellfish were identified in the estuary, including pearl oysters(Pinctadaalbina/nigraspeciescomplex),hairymussel(Trichomyahirsuta)andleafoyster(Isognomon ephippium, identified by morphology only) that are capable of clumping,consolidatingrubble/shellsubstrateandcontributingtothediversityofrestoredshellfishreefhabitats.
Eachrockoysterspeciesrecorded,oracombination,couldbetargetedforshellfishreefrestoration,however,consideringthemoderndaydominanceofS.glomerataitisanobviouschoice.ThecurrentdistributionofS.glomerataintheNoosaestuaryappearstobelargelylimitedtotheintertidalzone,withonlysparseindividualsobservedsubtidally(likelyaresultofcomplexecologicalinteractionsbetweenenvironmentalconditions,predation,settlementandrecruitmentandotherdisturbance).Thisstudyidentifiedkeyshellfishspeciesinatropical/sub-tropicalsetting,whichwillinformthefuturedesignphaseofrestorationefforts,includinghabitatsuitabilitymodelsandotheraspectsoftheearlydesignofhabitats.Thisisexpectedtoresultinsignificantcostsavingsbyhelpingimprovetheefficiencyandefficacyofcurrentandfuturerestorationeffortsaimedatrevivingtheselostorthreatenedecosystems.Thisstudyalsoprovidesanexcellentopportunitytotrialinnovative‘environmentalDNA’(eDNA)techniquesforthedetectionofoysterspeciesthroughouttheestuary.eDNA(DNAshedbyorganismsintotheenvironment)canbeobtainedfromwater(orsoil)samples,andcanallowdetectionoforganismswithoutneedingtosurveylargenumbersof(potentiallypoorlyaccessible)sites.ThisprojectwillprovidethefirstcomparisonofoysterbiodiversityobtainedfromeDNAsamplingcomparedwithtraditionalphysicalsurveysthroughouttheestuary.Ifsuccessful,wewilldevelopanefficientmeansofevaluatingoysterpopulations,whichcanbeappliedintheNoosaRiverestuaryandtootherestuariesaroundtheworld.Theresultsfromthisaspectoftheprojectwillbepresentedinthefinalreport.
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2. ProjectBackground
Shellfishreefs(reefscomposedpredominatelyofbivalvemolluscs)arenotasfamous,orperhapsasbeautiful,ascoralreefs,butwereoncecommonalongAustralia’scoastline(Gilliesetal.,2018)(Figure1).Thesereefsprovideimportantecosystemfunctionsincludingcoastlineprotection,habitatprovision,carbonsequestration,foodprovision,andimprovementofwaterquality(Gilliesetal.,2018;Grabowskietal.,2012).TheimportanceofreefstoestuarieshasunderpinnedtherecognitionofshellfishreefsasawetlandhabitattypeaspartoftheConventiononWetlandsofInternationalImportance(TheRamsarConvention–habitattype‘Ga’)(Kasoaretal.,2015).Todayoysterreefsareconsideredgloballythreatened,withanestimated85percentofhistoricalreeflost(includingfromAustralia)(Becketal.,2011;Gilliesetal.,2018).Thefunctionallossofoysterreefhabitatshasbeenlinkedtooveralldeclinesinecosystemproductivity,particularlyoffishstocks,likelyduetothelossofforagingandnurseryhabitats(Gilbyetal.,2018).Thelossofshellfishreefshasbeenattributedtoseveralfactorsincludingoverexploitation,dredging,increasedsedimentation,disease,andfloodevents(Becketal.,2011).Thepersistenceofmanyofthesestressorsmaymeanthatthesereefscannotberestored(Gilbyetal.,2018).However,examplesofsuccessfulshellfishreefrestorationprojectsintheUnitedStates,andtheconfirmationofoystersurvivalandrecruitmentonvariousprojectswithinAustralia,includingwithintheNoosaRiverestuaryindicatethat,withsuitablereefrestorationdesign,ongoingmonitoringandmaintenance,manyoftheseecosystemsmaybeabletoberecovered.
Figure1. Intertidalremnantoysterreef,TurkeyBeach,Queensland
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IntheUSA,oysterrestorationisleadingthewayinestuarinerestorationthroughthecreationof“green”jobsfollowingtheUSeconomicdownturn(Edwardsetal.,2013).Theserestorationprojectsprovidesubstantiallocalemploymentandeconomicopportunitiesthroughthecreationofnaturalinfrastructurethatcanenhanceecosystemservices(includingcoastalprotection)worthmillionsofdollarsandsupportotherindustriesincludingfishing(boostingcommercialandrecreationalproductivity)andtourism(Grabowskietal.,2012;Petersonetal.,2003).DespiteevidenceofsubstantialdeclinesintheconditionofestuariesinAustraliaandcallstorestorethemtomaintainfisheriesproductivity(Gilliesetal.,2018),marinerestorationinAustraliahastypicallylaggedbehindtherestoftheworld.However,shellfishreefrestorationprojectsarerecentlygainingmomentumwithinAustralia,withseverallarge-scaleprojectsinvestingupwardsof$20milliontowardsrestorationefforts.TherearecurrentlyseveralinitiativeswithinAustraliathataimtoprovidescience-based,well-consideredrestorationofhabitatsthathavebeenlost,includingtherestorationofoysterreefs(www.shellfishrestoration.org.au).TwoprojectsarecurrentlyunderwayinQueensland;oneinPumicestonePassage(MoretonBay),andanotherintheNoosaRiverestuary.
ResearchintothehistoryoftheNoosaRiverestuaryhasrevealedextensiveIndigenoususeofoysters(evidencedbylargeshellmiddensandreferencesfromearlysettlers),andtheexistenceofalargeoysterfisheryinthelate19thandearly20thcenturies(Thurston,2015).Leasesweregrantedfrom1881onward,andoysterswereharvested,includingbydredge,formarketsinBrisbaneandbeyond(Thurston,2015).Evenafterlargeoystershadallbutdisappeared,harvestofyoungoystersalsooccurredbydredge,theseweretransportedliveandon-growninMoretonBay(Thurston,2015).By1930commercialoysterharvestingintheNoosaestuaryhadlargelyceased,yetpopulationshavestillnotrecovered(Thurston,2015).Itisthoughtthatthedredgingofoysterbanksremovedalargeproportionofthesubstraterequiredforoystersettlement,andthatthehumanmodificationsoftheestuary(particularlytheNoosaRivermouth)furtherreducedtheavailabilityandsuitabilityofhabitat(Thurston,2015).
ItisgenerallyassumedthattheoysterspeciesharvestedfromtheNoosaestuarywastheSydneyRockoyster,howeverhistoricalrecordspointtowardsmorphologicaldifferencesbetween‘dredge’and‘bank’shellfish(Saville-Kent,1891).ArecentsurveyofoysterspeciesaroundtheQueenslandcoasthasrevealedhigherthanexpecteddiversity,withanumberofcurrentlyunrecognisedspeciescommonlyfoundinsimilarhabitatstoSydneyRockoysters(McDougalletal.,2020).Itisthereforepossiblethatdredgeandbankoystersrepresentdistinctspecies;thiswouldhaveimportantimplicationsforshellfishreefrestorationprojectsandmayexplainwhysettlementhasnotbeenobservedonsubmergedsubstratesinareaswithhealthySydneyRockoysterpopulationsinsometrialswithintheNoosaestuary(Gilby,2018;TheNatureConservancyandEcologicalServiceProfessionals,2015).
InNoosa,anoysterrestorationprogramisunderwaytorestorerockoysterreefsthatwerethoughttohaveconsistedofSydneyrockoysters.Unexpectedly,earlyresultshaveindicatedthatseveraltypesofoysteraresettling–theidentityofthese‘other’oystersisunknown,andlikelyreflectsthepaucityofinformationregardingoysterbiodiversity,ratherthantherecruitmentofexoticspecies.Thesignificantlackofknowledgeofshellfishreefecosystems
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hasbeenhighlightedintheliteratureasapriorityforresearch,andpriorstudieshaveoftenoversimplifiedshellfishreefecosystems(Gilliesetal.,2018);manymoreoysterspeciesarecapableofformingreefs,andreefsareoftencomposedofmultipleshellfishspecies(McDougall,unpublisheddata).Interspecificdifferencesinbiologyandhabitatpreferencesmeanthatsomeoysterspeciesarelikelytobemoresuitableforreefrestorationprojectsthanothers,butthisknowledgeiscriticallylacking.Understandingwhichspeciesarebeingtargetedinreefrestorationprojectsisessentialforoptimaldesign,whichshouldtakeintoaccountthehabitatpreferencesofthespeciesnaturally(and/orhistorically)foundinthearea.Furthermore,increasingdiversityofecosystemscanimprovetheircapacitytorespondto,andrecoverfrom,futuredisturbances.
Understandingoftheecologyoftargetspeciesisanessentialcomponentforsuccessfulrestorationprojects,howeverduetotaxonomiccomplexitiesinthisimportantshellfishgroup,ithasbecomeevidentthatageneticscreenisnecessarytodeterminethewealthofshellfishdiversity.Thisinformationwouldinformdesignoflarge-scalerestorationinitiatives,andaddressesanimportantknowledgegapidentifiedduringthetrialreefrestorationphaseinNoosa.Therefore,theaimsofthisprojectwereto:
1. EvaluatethedistributionanddiversityofoysterspecieswithintheNoosaestuary.2. Evaluatethesettlementpreferencesofdetectedoysterspecies.3. InvestigatetheutilityofeDNAfordetectionandmonitoringofoysterbiodiversityinthe
estuary.
3. Methods
Ambientwaterquality
Waterqualityparametersweremeasuredinsurfacewaters(30cmbelowthesurface)ateachsiteonseveraldaysduringdeploymentofsettlementplatesandwhilecollectingeDNAsamples.WaterqualitywasloggedusingaYSIProDSSmulti-parameterwaterqualitysonde.TheunitwascalibratedpriortodeploymentmanufacturercalibrationmethodsandsamplingcompletedinaccordancewiththeQueenslandMonitoringandSamplingManual2018(DepartmentofEnvironmentandScience,2018)forthefollowingparameters:watertemperature;dissolvedOxygen;specificconductance;salinity;pH;and,turbidity.
Aim1-EvaluatethedistributionanddiversityofoysterspecieswithintheNoosaestuary.
SamplingofoystersintheNoosaEstuarywasconductedbyfootonthe18thofDecember2019andbyboatonthe24thofAugust2020.Eightcollectionsiteswereselectedbasedontheavailabilityofhardsubstrateandthepresenceofoysters(Figure2).Waterqualityparameterswererecordedateachsite.Betweenthreeandtwelvespecimenswerecollectedateachsitedependingontheobservedmorphologicaldiversityapparentinthepopulation.Oysterswerestoredincoolerboxesoniceandreturnedtothelaboratory,wheresampleswerestoredin70%ethanoluntilprocessed.NoadultoysterswereobservedonmangroverootsatsiteSD1althoughoystersdidsettleonexperimentalsettlementplates.
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Figure2. SitesinthelowerNoosaEstuary.Bluedots:adultoystercollectionsite.Blackdots:settlementrackdeploymentsite.Pinkdots:eDNAsamplecollectionsite.
Oysterswerephotographed,shucked,andasmallsampleofadductormusclewasdissected.ExtractionswereperformedusingtheDNeasyBloodandTissueDNAKit(Qiagen)asperthe
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Oyster Survey Sites
±0 0.5 1 1.5 20.25Kilometers
Datum: GDA2020 Zone 56JData Sources:© State of Queensland.All care has been taken to ensure the accuracy of data. However,Griffith University make no representations or warranties about the accuracy, reliability or suitability and disclaims all liability for expenses, damages and costs incurred due to the data being incomplete or inaccurate.
LegendSurvey Sites
Adult Oyster Collection
Settlement Plates
eDNA
Noosa Heads
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manufacturer’sinstructions.Apartialfragmentofthe16SgenewasamplifiedbyPCRusingthetheprimers16S_Fwd(Banksetal.,1993)and16Sbr-H(Palumbietal.,1991)andthefollowingthermoprofile:95°Cfor30seconds,followedby30cyclesof95°Cfor1minute,51°Cfor1minuteand68°Cfor1minute,andafinalextensionat68°Cfor5minutes.PCRproductsweregelpurifiedandsenttoMacrogen(SouthKorea)forsequencing.Resultingtraceswerequalitytrimmed.Speciesidentificationwasperformedbyaligningtheresultingsequencesagainstanin-housedatabaseofoyster16Ssequences.
Aim2-Evaluatethesettlementpreferencesofdetectedoysterspecies.
Settlementracksweredeployedatthreesitesonthe18thofDecember2019(Figure2).Rackscontainedpairedstackedplates(onenylon,oneconcrete),withfourpairsplacedhorizontallyonthetopoftheunit,andfourpositionedverticallyattheendoftheposts(Figure3).Treatedshells(bothSROandPacific)werecable-tiedontoeachoftheposts(4ofeachspeciesoneachrack).UnitsweredeployedattwoexistingrestorationsitesandonenewsiteinLakeDoonella,andwerepositionedinordertobeexposedduringlowtide.Waterqualityparameterswererecordedateachsite.
Figure3. Settlementplaterackdesign.Top:constructionofsettlementracks.Bottom:settlementrackinsituatsiteSD1.
Settlementplateswerecollectedon8thofMay2020.Theabundanceofattachedspatwasrecorded(basedonmorphology),individualswerephotographed,andtheneachindividualwascarefullyremoved(avoidingcrosscontamination)andpreservedseparatelyin70%
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ethanolforsequencing.DNAextractionand16SPCRwasperformedasdescribedabove.Differencesinthedistributionandabundanceofrockoysterswerecomparedamongthetypesofsettlementplates(cementsheetandnylon),surfaceorientations(verticalandhorizontal),andsitesusingathreefactorPERMANOVA.UntransformedoysterabundancewasconvertedtoEuclideandistancematrixpriortoanalysis.Duetosubstantiallossesoftheoystershelltreatmentatsomesites,thesewereexcludedfromformalstatisticalanalyses;however,wheresettlementontooystershelloccurred,theresultsforcomparisonwiththeothertreatments.
Aim3-InvestigatetheutilityofeDNAfordetectionandmonitoringofoysterbiodiversity.
Watersamples(2Lwatersample,fourreplicatespersite)weretakenintosterileplasticcontainersatthreesitesvisitedonthe24thofAugust,2020(Figure2),fromsiteE1atslacklowtide,siteE3onanincomingtide,andsiteE2atslackhightide.Samplesweretakenfromthemiddleofthechannelandapproximately10cmbelowthesurface.Watersampleswerekeptoniceinthefieldandat4°Cuponreturntothelaboratory,andwerefilteredthroughsterile250mL0.45µmcellulosenitratefilterfunnels(Nalgene145-2045)usingavacuummanifold.Filtrationwascompletedwithin24hoursofsamplecollection.Threeadditionalsterileplasticcontainerswerefiledwithwaterfromthelaboratorysink(waterthebottleshadbeenrinsedin)andfilteredtoprovidenegativecontrols.DNAextractionwasperformedusingtheDNeasyBloodandTissuekit(Qiagen)protocol,withamodifiedlysisstepasperformedbyAlexanderetal.,2019.
4. ResultsandDiscussion
Characterisationofcollectionsites
CollectionsitesspannedfromtheNoosaRivermouthupstreamtotheentrancetoLakeCooroibah,andincludedsitesinLakeDoonellaandWeybaCreek(Figure2).Thewaterqualityparametersmeasuredinsituatthevarioussitesweretypicalofthatinlowertomid-estuarinewaters,withtemerpaturereflectingtheambientairtemperature,gooddissolvedoxygenconcentrationandpHtypicalofseawater(Table1).Turbidityrangedfrom1to39NTU,withthehighestrecordsoccurringinLakeDoonella(siteSD1).Theexceptionwassalinity(andspecificconductance),whichtypicallyrangedfrom23to42PSU.ThehighestrecordsoccurredatsitesinWeybaCreek(sitesS12&S13)inDecember2019(Table1),followinganextremelydryperiodwithverylowrainfall.Thesehypersalineconditionsexceededthenormalgrowingconditions;however,salinitymeasuredinMarch2020followingrainfallhaddeclinedtoexpectedsalinitylevels,andwellwithintheoptimalgrowthrangeforrockoysters(Table2).
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Table1. Waterqualityparametersmeasuredinsituateachsite
Site Date Time WaterTemperature(°C)
DissolvedOxygen(mg/L)
SpecificConductance(µS/cm)
Salinity(psu)
pH Turbidty(NTU)
SD1 18/12/19 12:36 26.89 6.54 53572 35.33 7.98 9.49 30/4/20 15:15 29.22 8.37 36746 23.14 8.11 39.03 8/5/20 11:00 22.07 6.57 52437 34.59 7.92 12.09A5/S12 18/12/19 11:29 25.53 7.44 61798 41.56 7.87 3.09 30/4/20 Nodata Nodata Nodata Nodata Nodata Nodata Nodata 8/5/20 15:21 23.17 7.49 45396 29.42 8.03 5.64A6/S13 18/12/19 9:45 23.85 7.26 62662 42.26 7.81 8.24 30/4/20 13:00 25.20 6.91 41210 26.38 8.05 4.89 8/5/20 12:35 22.51 7.15 48062 31.36 8.00 3.31A4 24/8/20 9:20 17.83 7.57 49615 32.52 8.22 2.81E1 24/8/20 8:16 18.00 7.22 50393 33.09 8.16 0.99E2 18/12/19 13:00 25.90 6.25 54201 35.82 7.97 6.67 24/8/20 14:06 18.90 7.58 51590 33.98 8.20 1.48A8/E3 24/8/20 12:28 16.61 7.39 46727 30.41 8.05 5.22A1 24/8/20 10:41 19.40 7.50 53330 35.27 8.32 9.64A2 24/8/20 10:04 18.17 7.37 51475 33.89 8.24 1.21A3 24/8/20 8:30 17.50 7.22 49667 32.56 8.18 1.08
ThedistributionanddiversityofoysterspecieswithintheNoosaestuary.
16Sfragmentsweresuccessfullyamplifiedandsequencedfor39oysterscollectedthroughouttheNoosaEstuary.Sequenceanalysisrevealedthattheoystersbelongedtothreedifferentspecies;Saccostreaglomerata(Sydneyrockoyster),SaccostrealineageBandSaccostrealineageG.TheuseofSaccostrea‘lineages’asopposedtospeciesisestablishedintheliteraturebecausethedifficultyinmorphologicallyidentifyingoysterspecieshaspreventedtheconfidentassignmentofspeciesnames(LamandMorton,2006;SekinoandYamashita,2016).Indeed,inthisstudyitwasimpossibletodistinguishSaccostreaglomerataandSaccostrealineageGmorphologically(Figure4).A16Sfragmentwasalsocollectedfora‘hairymussel’collectedfromsiteA2.ThesequenceconfirmsthatthisspeciesisTrichomyahirsuta.
ThefindingofSaccostreaglomerataintheNoosaEstuarywasexpected,andiscongruentwiththeknownnaturaldistributionofthespecies(fromtheTownofSeventeenSeventyinQueenslandtotheBassStrait,andNewZealand).SaccostrealineageBwaspreviouslyreportedfromYepoonandCairns(LamandMorton,2006),andbothSaccostrealineagesBandGwerefoundtobebroadlydistributedinQueenlandinarecentsurvey(McDougalletal.,2020).ThesetwospecieshavebroadIndo-Pacificdistributions,occurringasfarnorthasJapan(SekinoandYamashita,2016).
Saccostreaglomeratawasfoundatallsitessurveyed,otherthansiteSD1atwhichnoadultoysterswerefound.SaccostrealineageGwasfoundatsitesclosetotherivermouthandatTewantinboatramp(sitesA1,A2andA7),butnotinWeybaCreek,LakeDoonella,oratthemouthoflakeCooroibah.SaccostrealineageBwasfoundneartherivermouthonly(siteA1,howeverjuvenilesofthisspecieswereobservedatsiteA2also).Theseresultsindicatethatthethreespecieshavedifferenthabitatrequirements;thismayberelatedtodifferentsalinitytolerancesand/orabilitytowithstandsedimentation.
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Figure4. MorphologyofadultSaccostreaglomerataandSaccostrealineageG.
Theaccommodationspacerepresentstheareainanestuarywithenvironmentalconditionssuitableforgrowthofoysters(Volety,2013).Oystersgrowfromtheintertidaltodepthsofatleast20metresandthisiswheremuchofthehandgatheringordredgingofoystershashistoricallyoccurred(Nell,2001).However,itisthoughtthatduetochangesinambientconditionsandavarietyofexternalfactors,rockoystersinSouthernQueenslandaretypicallyfoundonlyintheintertidalzoneandhavebeenfunctionallylostfromsubtidalhabitats(Diggles,2013).ConditionssuitableforoptimalSaccostreaglomeratagrowtharesummarisedbelowfrom(Holliday,1995;NellandHolliday,1988;Rubio,2007).Adultrockoystersareabletoclosetheirvalveforseveraldaysifsalinityislessthan15ppt,althoughprolongedperiodsoflowsalinitycancausedeath(Holliday,1995;NellandHolliday,1988).Basedonambientconditions,itwouldbepossibleforoysterstogrowatanyofthesitessurveyed,wheresuitablesubtsrataisavailableforsettlement(Figure5&6).Optimalconditionsfortheotherbivalvespeciesidentifiedwithinthisstudyarenotpresentlyknown.
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Table2. TemperatureandsalinityforoptimumgrowthandtolerancelimitforSaccostreaglomerata
Parameter Units Life History Stage Larvae Spat Adult Temperature optimum growth °C 24-26 14-28 18-26 Temperature tolerance limit °C unknown 11-30 11-30 Salinity optimum growth ppt 23-39 20-40 25-35 Salinity tolerance limit ppt 15-39 0-40 0-50
Figure5. SubtidalrockrubbleandoysterbankatTewantin
Figure6. LowreliefaggregationofsubtidalleafoysterbedoversandandmudinWeybaCreek
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SettlementpreferencesofoysterspeciesintheNoosaestuary
DNAfragmentsweresequencefromatotalof44oysterspatcollectedonsettlementracksatthreesitesthroughouttheestuary.Threespeciesweredetected;Saccostreaglomerata,SaccostrealineageG,andOstreaequestris.OstreaequestrishasawidedistributioninbothAtlanticandPacificoceans,includingArgentina,U.S.A.,Japan,ChinaandNewZealand(Huetal.,2019).ThepresenceofthespeciesinAustraliahas,untilnow,notbeenconfirmedwithgeneticevidence(althoughspecimensofthesamespecieswerepreviouslydiscoveredonsettlementplatesinthePumicestonePassage,McDougallunpublisheddata).Itisasubtidalspecies(whichexplainswhyitwasnotfoundintheadultoystersurveys,whichpredominatelyexploredtheintertidalzone),andisreportedtosurviveinhighsalinityenvironments(GaltsoffandMerrill,1962).Twosmallpearloysterspecimenswerealsosequenced;theybothbelongtothePinctadaalbina/nigraspeciescomplex.
Theexternalmorphologyofoysterspatwasrecordedinphotographstakenpriortodissection.Oncesequencingresultshadbeenreturnedphotographswereexaminedtodeterminewhetherspeciescouldbereliablyidentifiedbymorphology.Extensiveoverlappingvariationwasobservedacrossthethreespecies(Figure)indicatingthatmorphologicalidentificationisnotfeasible.
AllthreespeciessettledontoplatesatsitesS12andS13(WeybaCreek),howeveronlySaccostreaglomerataspatweredetectedatsiteSD1(LakeDoonella).Thisisincontrastwithadultoysterdistributions,withonlySaccostreaglomerataadultsdetectedatsitesS12andS13.Thelackorreducedabundanceofotherspecies(specifically,SaccostrealineageG)atthesesitesisnotduetolackoflarvalrecruitment,butmostlikelyduetounfavourableenvironmentalconditionsthatcausemortalityofsettledindividualsenablingthenumericaldominanceofS.glomerata.SpatofSaccostrealineageBwerenotdetectedonanyoftheplates;thiscouldhaveseveralexplanations,forexample,lackoflarvalsupply(adultsofthespecieswereonlydetectedattherivermouth),lackofsuitabilityofplatesforsettlement,earlymortality,orthelackofaspawningevent.Itisnotablethatthe2019/2020summerwasparticularlydry,possiblyaffectingspawningbehaviour.Adultsweregenerallyinlowdensitieswhererecordedatthemouthoftheriver.
Thereweredifferencesinthedensity(individualsper0.01m2)ofoystersonplatesaroundtheestuaryaswellasondifferentsurfaceorientationsandtypesofsettlementsurface(Table:PERMANOVAsitexorientationinteractionpseudo-F2,36=5.55,p=0.002,Figure8&9).Therewasalsoageneralincreaseinthedensityofoysterssettlingontonylonthanconcretesheet(Table:PERMANOVAsubstratetypepseudo-F1,36=4.56,p=0.029,Figure8).Theaveragedensitywasgreatestonhorizontalsurfaces,particularlyontheundersidesofplates.Alayerofsedimenthadaccumulatedontheuppersurfaceofeachplate(Figure,upto5mmthickonsomeplates),whichpreventedsuccessfulattachment.ThegreatestdensityofoysterswasrecordedatsiteS12,whichisclosesttothemouthofWeybaCreek.Onverticalsurfaces,thedensityofrecentlysettledoysterspatontooystershellswastypicallysimilartothatfoundonverticalnylonsheetsatsiteS12,butmuchgreaterthanonoystershellthanontheplatesatsiteS13(Figure).
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Figure7. Morphologyofspatofeachdetectedspecies.
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Figure8. Averageabundance(±SE)ofrockoystersonhorizontalsettlementplatesamongsites
Figure9. Averageabundance(±SE)ofrockoystersonverticalsettlementplatesamongsites
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12.0
14.0
16.0
18.0
20.0
DS1 S12 S13
Mea
n ab
unda
nce
(ind.
/0.0
1m2
)(±SE
)
Site
Concrete sheet Nylon Oyster shell
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Table3. PERMANOVAresultsfordifferencesinoysterdensityamongsite,substratetypesandsurfaceorientations.
Factor df MS Pseudo-F P(perm)Site 2 1654 20.16 0.001
SubstrateType 1 374 4.56 0.029Orientation 1 884 10.77 0.002
SitexSubstrateType 2 221 2.69 0.081SitexOrientation 2 455 5.55 0.002
SubstrateTypexOrientation 1 96 1.17 0.302
SitexSubstrateTypexOrientation 2 28 0.34 0.743Error 36 82
PariwiseComparisons (b)HorizontalvsVertical
t-value P(perm)
S12 2.68 0.010 S13 4.11 0.002
DS1 4.43 0.001 (c)Horizontal (d)Vertical
Differencesbetweensites t-value P(perm) t-value P(perm)S12vsS13 3.53 0.005 3.12 0.004
S12vsDS1 3.76 0.003 3.22 0.003
S13vsDS1 2.10 0.061 0.68 0.586
Figure10. SettlmentplateswithhighcoverageofsedimentonuppersurfaceinMay2020
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Comparisonofmethodsforspeciesdetection
Neitherofthetwomethodsofspeciesdetectioninvestigatedsofar(adultoystersurveysorsettlementplates)gaveacomprehensivepictureofthespeciespresentwithintheNoosaestuary.Itispossiblethatadditionalspeciesremaintobedetected,particularlythosethatoccursubtidally.Oystersurveyswouldpossiblyhavebeenmorecompletehadsubtidalcollectiontechniquesbeenutilised,andadditionalspeciesmayhavebeencollectedonsettlementplatesiftheyhadbeendeployedatadditionalsites.Eachofthesemodificationpresentsadditionallogisticalchallenges;useofdiversforcollectionisexpensive(anddredgeshit-and-miss),andsettlementplatesdeployedatlocationswithhigherhumantraffic(suchasaroundtherivermouth)aremorelikelytobeinterferedwith.WeawaittheresultsoftheeDNAsamplingtoseeifthisprovidesamorerobustwaytodetecttherangeofspeciespresent(includingamixofbothadultsandspat).Untilthen,itappearsthatusingacombinationoftechniquesisneededtodetermineaccuratelythecompositionofoysterassemblagesinestuaries,andinparticularontohabitatrestorationunits.
Historicalsignificanceandimplicationsforshellfishdesign
ThehistoricalpresenceofoystersintheNoosaestuaryiswellrecorded,bothwithinmiddensandintheliterature(Thurston,2015).Whilenomentionismadeofthespeciesofoysterpresent,‘bank’and‘dredge’oystersaredistinguished.Saville-Kent(1891)believedthattheserepresentedtwoformsofSaccostreaglomerata,andnotedthatthedifferenceinmorphologywaslikelyanenvironmentaleffect,withsubtidal‘dredge’oystershaving‘asmootherandmoreponderousform,withoftenanabnormallyelongatedcontour,andamoreorlesscompleteabsenceoftheconspicuouscolourationcharacteristicoftheshellsexposedtolightandair’.Despitethis,healsonotedthatthetwo‘forms’ofoystersoccurredwithinthesameclump,leavingopenthepossibilitythattheyaredistinctspecies.Inadditiontothesereports,anewspaperarticlefrom1915authoredbyHarryC.Perrystatesthat‘MudoystersareplentifulinLakeWeyba’(Perry,1915).While‘mudoysters’insouthernstatesrefertoOstreaangasi,thespeciesdoesnotoccurinQueensland.Otherarticlesindicatethattheterm‘mudoyster’wasusedforanyoysteroccurringbelowthelowwatermark(1934).Giventhedifficultyindistinguishingoysterspeciesbymorphology,determiningwhatspecieswerehistoricallypresentintheNoosaestuarywillbechallenging,particularlyiflivingspecimenshavebecomelocallyextinctandarcheologicalevidencefrommiddensneedstobereliedupon.Saccostreaglomerata,SaccostrealineageGandSaccostrealineageBaremorphologicallyverysimilarasadults,andwerelikelyconsideredtheonespeciesinhistoricalaccounts.Whetheraccuratedeterminationscanbemadefrommiddenspecimensremainstobeestablished.
ThisstudyhasshownthatthereareatleastfourspeciesofrockoysterpresentintheNoosaestuary,presumablyeachofthese,oracombination,couldbetargetedforshellfishreefrestoration.Giventhateachspecieslikelyhasuniqueenvironmentalrequirements,andthatmodellingforappropriatereefrestorationsitesisgenerallybasedonparametersforSaccostreaglomerata,considerationofalternativespeciesmaysignificantlyincreasethenumberofpossiblesites.Thedetectionofasubtidalspecies,Ostreaequestris,suggeststhat
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submergedreefsmaybepossible;however,reportsindicatethatthespeciesdoesnotnaturallyformreefs(GaltsoffandMerrill,1962).Giventheresultspresentedhere,werecommendtrialstoexploretheattributesofeachspecies(resilience,performance,provisionofecosystemservices)underdifferentenvironmentalconditionstoprovideessentialbaselineinformationtointegratewithshellfishreefrestorationdesigns.
5. AcknowledgementsTheauthorswouldliketoacknowledgetheprojectfunders,GriffithUniversityandtheNoosaBiosphereReserveFoundation,NikolinaNenadic for laboratoryassistance,andBryanWalshfromtheNoosaParksAssociationforfieldassistance.
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