Responses of subtropical seagrasses to fluctuations in salinity within an experimental facility

218 Pages·2002·8.7 MB·English

by  Chesnes, Thomas C.,

RESPONSESOFSUBTROPICALSEAGRASSESTOFLUCTUATIONSIN
SALINITYWITHINANEXPERIMENTALFACILITY
ADISSERTATIONPRESENTEDTOTHEGRADUATESCHOOL
OFTHEUNIVERSITYOFFLORIDAINPARTIALFULFILLMENT
OFTHEREQUIREMENTSFORTHEDEGREEOF
DOCTOROFPHILOSOPHY '
UNIVERSITYOFFLORIDA
2002
Copyright2002
By
ThomasChesnes
ThismanuscriptisdedicatedtoRoseTrivigno.
Iknowthatyouwouldbeproud.
ACKNOWLEDGMENTS
Wordscannotexpressmyappreciationforthosewhosupportedmeinthis
endeavor. Mysupervisorycommitteehasbeenwithoutadoubtinstrumentaltomy
success.IthankEvanChipourasforhissupportfromtheearlieststagesofthisproject,as
wellashisabilitytohelpmekeepthingsinperspective. IthankFrankNordliefor
introducingmetoecologicalresearchandmentoringmyundergraduateproject. Without
him,Icertainlywouldnotbeinthisprofession. IthankStephenDavis,whose
enthusiasmforalgaeiscontagiousandinspiring. IespeciallythankThomasCrisman
whohelpedreintroducemetomyecologicalroots. Hispatienceandassistancewere
essentialingettingthroughadifficultperiod. Lastly,IthankmychairmanClay
Montague,whosemixofhumorandscientificcuriosityhasinspiredmetodevelopa
strongscientificethic,aninterestintheworkingsoftheuniverse(onalltemporaland
spatialscales),andanever-endingpursuitoftruthoveracceptedideas.
Thisstudywouldnotbepossiblewithoutfundingandlogisticalsupportfromthe
EvergladesNationalParkInteragencyScienceCenterinKeyLargo,Floridaandthe
SouthFloridaWaterManagementDistrict,whoalsoprovidednutrientanalysis. The
AylesworthFoundationandGreeningUFprovidedadditionalsupport. Specialthanksto
thosewhoassistedindatacollection:CasieRegan,ChristosAnastasiou,JoelDudas,
JessicaDiEgidio,BenLoughran,andlast,butcertainlynotleast,BridgetChesnes.
Finally,Igivethankstomyfamilyandfriendswhohavealwayssupportedme. I
amtrulyblessed.
IV
TABLEOFCONTENTS
page
ACKNOWLEDGMENTS
iv
ABSTRACT vii
CHAPTERS
1INTRODUCTION 1
2DESCRIPTIONOFFACILITYDESIGNEDFORSALINITYFLUCTUATIONAND
PILOTSTUDY 9
DescriptionofFacility 9
MaterialsandMethodsofPilotStudy 13
ResultsofPilotStudy 16
DiscussionofPilotStudy 24
3MATERIALSANDMETHODSFORMAINSTUDY 28
SeagrassCollectionandAcclimation 28
DescriptionandProtocolofFacilityExperiments 29
DataandStatisticalAnalysis 35
4RESULTSOFEXPERIMENTS2THROUGH7INTHESALINITYFLUCTUATION
FACILITYONKEYLARGO 39
Experiment2:EffectofAmplitudeofSalinityFluctuationonSeagrasses 39
Experiment3:RateofChangeofSalinityFluctuation(Pyramidvs.SquareWave)....58
Experiment4:SalinityFluctuationaroundDifferentMeans 78
Experiment5:ExtremeSalinityFluctuationandEffectofPeriod 96
Experiment6:SalinityFluctuationandCirculation:ConstantThroughFlowofWater
vs.AirCirculationinExperimentalTanks 114
Experiment7:EffectofSalinityFluctuationandReductionofLight 134
5CORRELATIONSBETWEENBIOLOGICALMEASUREMENTSANDPHYSICAL
VARIABLESINFACILITYEXPERIMENTS 147
CorrelationswithSalinity 147
CorrelationswithTemperature,Light,andWaterClarity 155
CorrelationswithWaterNutrientConcentrations 160
CorrelationswithFieldConditionsatCollectionSites 165
6PRODUCTIVITYANDLEAFOSMOLALITY-RESULTSOFEXPERIMENT8...173
Introduction 173
MaterialsandMethods 175
DataAnalysisforExperiment8 178
Results 179
Discussion 190
7DISCUSSION 196
OverallDiscussion 196
Conclusions 201
REFERENCES 203
BIOGRAPHICALSKETCH 207
VI
AbstractofDissertationPresentedtotheGraduateSchool
oftheUniversityofFloridainPartialFulfillmentofthe
RequirementsfortheDegreeofDoctorofPhilosophy
RESPONSESOFSUBTROPICALSEAGRASSESTOFLUCTUATIONSIN
SALINITYWITHINANEXPERIMENTALFACILITY
By
ThomasC.Chesnes
May2002
Chairman: ClayL.Montague
MajorDepartment: EnvironmentalEngineeringSciences
Thesparsityofseagrasscommunitieswithinthepondsandbaysofnorthern
FloridaBaymaybeduetothewidefluctuationsofsalinityinthesehabitats. Seven
experimentswereperformedinafacilitydesignedforsalinityfluctuation. Threeseagrass
species,Thalassiatestudinum,Halodulewrightii,andRuppiamaritima,were
transplantedtothefacilityandsubjectedtovaryingdegreesofsalinityfluctuation.
Treatmentswerevariedaccordingtosalinitywavemean,amplitude,frequency,and
suddenness(slope)ofchange.Twoexperimentscrossedtheeffectsofsalinityfluctuation
withmethodsofwatercirculationandreductionsinavailablelight. Afinalexperiment,
performedinbuckets,measuredthephotosyntheticandinternalosmoticresponsesof
seagrassestofluctuationsinsalinity.
Toassessthelossofphotosyntheticmaterialintheseagrassesduringthe
experiments,agreenleafindex(GLI)wasdeveloped,basedonthepercentgreenleaves
vn
presentperturion,proratedforpartialgreencoloration. Leafandrhizomemorphometries
weremeasuredpriortoandfollowingthetreatments.
Thalassiawasthemostsensitivetosalinityfluctuation. Biologicalparameters
werenegativelycorrelatedwithincreasingsalinitywaveamplitudes,frequencies,and
suddennessofchange. Theeffectofsalinityfluctuationwasdampenedwhensalinity
fluctuatedwithinarangeofhighersalinities. Salinityfluctuationwasmoreofan
influenceonThalassiasurvivalthanthereductionoflight.
Haloduleconditionwasimpairedbysalinityfluctuation,butnottotheextent
experiencedbyThalassia. Greenleafindicesdecreasedwithincreasesinsalinitywave
amplitude,frequency,andslope. Thenumberofturionspersprigcorrelatednegatively
withincreasingamplitudeandmoresuddenchangesinsalinity.Halodulesurvivalwas
enhancedbyfluctuationswithinahighersalinityrange.
Ruppiawasthemostresilientoftheseagrassspeciestested. Thisseagrasswas
abletosurviveallofthesalinityfluctuationtreatments. Increasingthefrequencyof
salinitychangedidhaveanegativeimpactonthisseagrass,resultinginlowergreenleaf
indicesandnumberofleaves.
Inordertosurvivefluctuatingsalinities,seagrassesmustregulatetheirinternal
osmoticconcentrationsinrelationtotheirsurroundingwaters. Ruppiaosmoregulated
morequicklythanThalassiaandHaloduleandmaybethekeytoitsresiliency.
Vlll
CHAPTER
1
INTRODUCTION
Since1881,humanactivitieshavedisruptedthenaturalflowoffreshwaterfrom
theEvergladesintoFloridaBay(FourqureanandRobblee1999). TheEverglades
watershedhasbeenengineeredandmanagedforagriculture,floodcontrol,andwater
supplyforthegrowingpopulationinSouthFlorida(LightandDineen1994). Water
managementprotocolsinvolvingalterationsinfreshwaterflowcanchangetheregimeof
salinityfluctuationsinthedownstreamestuary. Suddenreleasesoffloodwatermay
createrapiddropsinsalinity,whereaswaterheldbackintimesofdroughtmayamplify
salinityincreasesdownstream(MontagueandLey1993). Changesincommunity
structurewillbemostnoticeableintheestuarinesalinityfieldsclosesttoland(Estevez
2000).
Salinityrelatedproblemsarisewhenestuariesreceivetoomuchortoolittlefresh
water,orwateratimpropertimes(Odum1970). Thesehabitatsarecharacterizedas
beingharshduetothesalinitychanges,especiallywhencomparedtothemorestatic
conditionstypifyingmarineorfreshwaterhabitats(DeatonandGreenberg1986).
Changesinsalinityoccurrapidlyintheshallowbasinslocatedwithinthenorthernland
marginofFloridaBay. Periodsofhighfreshwaterinflowduringtheonsetoftherainy
season,intropicalstorms(Chesnes1999),orwatermanagementreleasescancauseareas
withmarinestrengthsalinitiestobecomefresh,insomecaseswithinamatterofdays
(Mclvoretal.1994,MontagueandChipouras1998).
Themeteorologicallydrivenpatternsofsalinityareclearlyseeninthesalinity
recordofLittleMadeiraBay,locatedwithinthenorthernlandmarginofFloridaBay
(Figure1-1). Duringthecourseofthedryseason,salinitysteadilyrosefrom10%o
(December1998)toabove30%o(May1999). Attheonsetofthewetseason(May/June
1999),salinitydroppednearly20%ointhefirstweek,andapproximately30%owithin
three.
Acutefluctuationsinsalinityalsooccurredduringthistimeperiod. DuringJuly
andAugustof1998,salinityfluctuatedbetween1and18%o,withaperiodof
approximately4daysbetweenpeaksandtroughs. Theamplitudeofthefluctuation
variedoverthecourseofthemonth(Figure1-1). Acutefluctuationsalsooccurredin
OctoberandDecemberof1998,January1999,andagaininthelatesummer/early
autumnof1999. TheamplitudeofsalinitychangewashigherinJulyandAugustof1999
thanin1998,whenchangesofover20%owereseenoverfourdayperiods.
Thepatternofsalinitychangeduringtransitionfromhightolowsalinityinthe
pondsandbaysofthelandmarginofFloridaBayismoreacutethanduringthetransition
fromlowtohigh(MontagueandChipouras1998). Increasesinsalinitycanbecausedby
evaporationduringthedryseasonorbywindspushingsalinewaterfromFloridaBayinto
theestuary. Thetransitiontosaltierconditionsisthoughttobemoregradual,andthe
lossofstenohalinefreshwatermacrophytesmaybeamoreprogressiveprocessasthe
salinityslowlybecomeselevated.Conversely,asharpdeclineintheabundanceof