!!! Seasonal!Variation!of!Zooplankton!Nutritional!Quality!at!a!Reef! Manta!Ray!(Mobula'alfredi)!Feeding!Ground!on!Ningaloo!Reef!

Transcription

1 SeasonalVariationofZooplanktonNutritionalQualityataReef MantaRay(Mobula'alfredi)FeedingGroundonNingalooReef Submittedby AlexandraThornton ThisthesisispresentedforthedegreeofBachelorofScienceHonours,SchoolofVeterinary andlifesciences,ofmurdochuniversity,2017

2 Declaration Ideclarethatthisthesisismyownaccountofmyresearchandcontainsasitsmaincontent work,whichhasnotpreviouslybeensubmittedforadegreeatanytertiaryeducation institution. AlexandraThornton 2

3 Acknowledgements First of all, I would like to thank my amazing supervisors Mike van Keulen and Frazer McGregor,whoseexpertiseandadviceIcouldnothavedonewithout.Thankyouforbeingso supportiveandbelievinginme,evenwhenididnot.andthankyouforremindingmeofthe importanceofworklifebalance.ifeelincrediblyluckytoabletohavenotjustsupervisors, butincrediblementorswhomi malsoluckytocallfriends.aspecialthankyoutomyfield workpartnerincrimetarryncoward,forsuchgreatfieldtripsandlatenightlabworkwithso manylaughs. I would also like to thank Asia and Amelia Armstrong whose assistance up in Coral Bay undertakingfieldworkwasinvaluable.yourknowledgeandadvicewassohelpful.iwouldalso liketothankthevolunteersfromtheearthwatchteamwhoassistedmewithmyfieldworkin May.ThankyoutoAlexKyddandKarenEigelandwhomhelpedoutwhilesamplingonthe tourvessel.aspecialmentiongoestoamberbennettwhoalsovolunteereddoingfieldwork and provided general moral support and invaluable friendship that helped keep me level headed.thankyoutoianmckernanforprovidingmewithallofmyfieldworkequipmentand beingasupportivefriend. ThankyoutoNavidMoheimaniforlettingmeusehislabfacilities,makingmefeelwelcome and teaming me up with Ashiwin Vadiveloo and Tasneema Ishika. They were both so incrediblyhelpfulwiththenutritionalanalysislabprocedures,andwillingtoanswerallofmy millionsofquestions,icouldnothavedoneitwithoutthemsothankyousomuch. IwouldliketosaythankyoutoLesleyBrainforhelpingmewiththestatisticalanalysisand for somehow making stats seem easier than I think it is. Thank you so much to Claire Greenwell and Stefan Brown for being such supportive friends, always willing to help and provideadvice,yourfriendshipsmeanalottome. 3

4 Finally,IwouldliketogiveaspecialmentiontoJeremyAlmanandmyfamilyforbeingso incrediblysupportiveandencouragingmetokeepatit,butremindingmetotakeadayoff everynowandthen.youaremyrocksandiamsogratefulforallyoursupportthroughout thislearningprocess. 4

5 TableofContents Abstract..7 Chapter1Introduction.9 1.1ZooplanktonBiodiversityandBiochemicalComponents Abundance,DistributionandSpeciesComposition BiochemicalComposition LipidsandFattyAcids Protein Carbohydrates Carbon:NitrogenRatio ImpactsofClimateChangeonPlanktonCompositionandDistribution PlanktivorousElasmobranchs MantaRays NingalooReef Aims.29 Chapter2MaterialsandMethods DescriptionofStudyArea ZooplanktonCollection SampleProcessing BiochemicalAnalysis StatisticalAnalysis.39 Chapter3Results EnvironmentalVariablesandObservations Biomass Carbon:NitrogenRatio NutritionalComponents LinktoMantaRayAggregations..48 Chapter4Discussion EnvironmentalVariablesandObservations 50 5

6 4.2Biomass Carbon:NitrogenRatio NutritionalComponents LinktoMantaRayAggregations RecommendationsforFutureStudiesontheNutritionalQualityofZooplankton Conclusion..63 References.65 Appendix1ProcedureforLipidExtraction 79 Appendix2ProcedureforProteinDetermination

7 Abstract Zooplankton provide a fundamental connection between primary producers and higher trophiclevelconsumers,supportingsomeofthelargestmarineanimalsaswellasmicrobial organisms.therefore,thenutritionalresourceofzooplanktonmustbesufficienttosupport a wide array of marine species. The nutritional quality(lipids, protein and carbohydrates) variesseasonallywithchangesinspeciescomposition,asdifferentorganismsstorevarying amountsofbiochemicalcomponents.theseseasonalvariationshavedirecteffectsonthe marinefoodweb,andthoseorganismsthatrelyuponthenutritionalresource.zooplankton has a spatiotemporally patchy distribution, with variations in species composition. This is reflectedbythevariabilityofeachbiochemicalcomponentwhencomparingregionsaround theworld. Thisstudyaimedtoquantifytheseasonalproportionsofzooplanktonnutritionalcomponents at Bateman Bay, Ningaloo Reef in Western Australia, in order to determine what planktivorousfishsuchasreefmantarays(mobula'alfredi)arereceivingyearround.feeding mantarayswereusedtolocatepatchesofplankton,andsampleswerecollectedviatowing a300µmmeshplanktonnetfromthebackofaboat.sampleswerecollectedfromfoursites in autumn and three sites in winter. All samples were analysed for lipids, protein, carbohydrates,totalorganiccarbonandnitrogen(c:nratio)andbiomass. All nutritional components varied significantly between seasons, and each site showed compositional variability, especially protein. Protein and lipids were significantly higher duringautumnthanwinter,whilecarbohydrateswerehigherduringwinter.thec:nratiowas significantlyhigherduringwinter,whenphytoplanktonabundancewashigher.biomasswas larger in winter when there was a greater abundance of portunid crab larvae, eggs and phytoplankton, however was not statistically significant. Environmental variables; temperature,turbidityandtidehadnocorrelationtozooplanktonbiomass,nutritionalvalue andreefmantarayfeeding.however,greaternutritionalquantitieswerefoundwhenmanta 7

8 rays were feeding, and the highest biomass was recorded when the largest feeding aggregationofreefmantarayswasobserved. This study has provided insight into the biochemical composition of mixed zooplankton populationsaroundbatemanbay,ningalooreefinautumnandwinter.itappearsthatmanta rays match their distribution to the zooplankton, and nutritional quantities proved to be higher during warmer temperatures. However, additional yearground sampling is recommendedforfuturestudies,inordertobetterunderstandthesepreliminaryfindings. Knowledgeofhowmantaraysrelyonareaswithhighnutritionalvaluewillhelptoexplain seasonalvariationsinreefmantarayvisitation,andprovidemanagementimplicationsforthe conservationofthisspecies. 8

9 Introduction 1.Zooplankton Zooplankton are essential to the functioning of marine food webs because of their high abundanceandfundamentalecologicalroles(richardson2008;lequéréet'al.2016).they provide a connection between primary producers and higher trophic level consumers (Dalsgaard et' al. 2003; Richardson 2008). Some of the largest animals on the earth (for example whale sharks (Rohner et' al. 2013a), blue whales (Buchan and Quiñones 2016), megamouth sharks (Tomita et' al. 2011) and basking sharks (Sims et' al. 2003)), rely on zooplankton to provide sufficient energy and nutrients for their survival. Zooplankton communitiesnotonlysupportlargemarineanimalsbutmicrobialorganismsaswell.benthic communitiesincludingcnidarians,echinodermsandanemonesrelyonzooplanktonlarvae, faecalmatteranddeadcarcassesforsustenanceastheygraduallyfalltotheseafloor(pepper et'al.2015;lequéréet'al.2016).theseorganismsandanimalwasteproductscontainmuch neededorganiccarbon(richardson2008),nitrogenandphosphorous,whichisrecycledby microbialorganisms(dubinskyandjokiel1994). Since zooplankton create fundamental links between primary producers and higher order consumers (Dalsgaard et' al. 2003), imbalances in environmental and biochemical compositioncannegativelyimpactconsumergrowth(mullergnavarra2008).stableisotope analysis has shown high variability in zooplankton community composition between shelteredreeflagoonsandoceanicouterreefareas(mccauleyet'al.2014).theseareasare subjecttovaryingoceanographicconditionsandthereforedifferenttrophiclevels(mccauley et'al.2014).themechanicalenergybehindoceanographicfrontsandeddieshasimportant implicationsforbiologicalactivityandproductivity(lebourgesgdhaussyet'al.2014).eddies attracthighertrophiclevelmarineanimalsbecausetheycreateareasofdense,easytoaccess prey(lebourgesgdhaussyet'al.2014).amesoscalecycloniceddyknownasthecapricorneddy in the southern Great Barrier Reef (GBR), is believed to greatly influence the manta ray 9

10 (Mobula'alfredi)aggregationsatLadyElliotIsland(LEI),wheretheyhavebeenseenforaging incloseproximitytotheeddy(weekset'al.2015). 1.1ZooplanktonBiodiversityandBiochemicalComponents Thenutritionalqualityofzooplankton(lipids,proteinandcarbohydrates)variesseasonally duetochangesinspeciescomposition,whichhasdirecteffectsonthemarinefoodweband fish that rely upon it(bascur et' al. 2017). For most fish a diet of high protein and a large amountofessentialfattyacidsandlipidsisessentialforgrowthandmetabolism(conceição et'al.2010),thereforeplanktoncommunitiesthatconsistofhighamountsoflipidssuggesta rich source of food(parrish et' al. 2005). Where, how and when a particular species feeds determinesreproductivesuccess,spatialecologyandnutritionalcondition,andcaninfluence their evolutionary pattern, such as speciation (Stewart et' al. 2016). The function of lipids variesbetweenzooplanktontaxa,fromgelatinousspecies,whichonlycontainaverysmall percentageoflipids,tocopepodswithover60%oflipiddrymass(leeet'al.2006).average nutritionalcompositionofzooplanktoninthesouthernocean,arabianseaandequatorial Pacific showed protein was most abundant, comprising approximately 65% of the total biomass,followedbycarbohydratesat19%andlipidsat16%(hedgeset'al.2002).theenergy storedwithinzooplanktonistransferredtoplanktivorousfishwhenconsumed(barroetaet' al.2017). Zooplankton has a spatiotemporally patchy distribution (Jagadeesan et' al. 2010), and the variabilityofeachbiochemicalcomponentcanbeseenwhencomparingregionsaroundthe world.planktondynamicsdifferstronglyinhightolowlatitudes;polarwatersaremuchmore productive than tropical or temperate waters, due to strong seasonal cycles(findlay et' al. 2006; Ji et' al. 2010). Phytoplankton biomass (often used as a proxy for zooplankton productivity),inthesouthernendofthehumboldtcurrentsystem,offchile,hasshowninterg seasonal variations due to environmental variables such as temperature and wind stress (Gomezet'al.2017).Windstressinfluencesplanktonbiomassmostsignificantlyinspringand summer, due to solar radiation enhancing phytoplankton s response to seasonal upwelling 10

11 duringthistime(gomezet'al.2017).speciescompositionhasalsobeenobservedtofluctuate withtheseseasonalevents,whichhasaneffectonprimaryandsecondaryproductionand local fisheries (Gomez et' al. 2017). Tidal variations also influence zooplankton biomass (Armstrong et' al. 2016). The average biomass of zooplankton off the Cabo Catoche in the YucatanPeninsula,Mexicohasbeenreportedas4.5gm g3 atplanktivorousfishfeedingsites (Mottaet'al.2010),whileaveragebiomassfluctuationsofbetween0.08and1.76gm g3 have beenreportedinthearabiansea(bhatet'al.1993),showingtherangeofbiomasspossiblein differentsystems. Duetothehighvariabilityofoceanographicconditionsandenvironmentalvariableswithin differentmarinesystems,itisdifficulttodetermineaglobalaveragerangeofthebiochemical components of marine plankton (Hedges et' al. 2002). During the Arabian Sea monsoon season,zooplanktoncompositionwasfoundtoconsistof41%protein,15%carbohydrates and 20% lipids of total dry mass (Jagadeesan et' al. 2010), whereas during dry season the averagebiochemicalcomponentswere34%protein,3%carbohydratesand9%lipids(bhatet' al.1993).nutritionalcomponentsofzooplanktonaroundnorthstradbrokeisland,southern GBR,werecalculatedas3%protein,3%carbohydrates,and22%lipids(Verlinden2010).The lowproteinfoundwasattributedtothemixedsubgtropicalzooplanktonpopulation(verlinden 2010). In the tropical Indian Ocean, protein represented 45% of the zooplankton, 7% carbohydratesand14%lipids(krishnakumariandgoswami1993).changesinbiochemical proportions,varywithseasonalspeciescomposition. 1.2Abundance,DistributionandSpeciesComposition Ifalloftheorganismswerehomogeneousthroughouttheocean,thenutritionalresources would be insufficient to sustain the high level of productivity observed (McManus and Woodson 2012). The ocean is structured horizontally and vertically as a result of thermodynamics,whichtogetherwithorganismbehaviourdrivesthepatchydistributionof predatorsandprey,thussupportingproductivityinvariousmarineenvironments(mcmanus and Woodson 2012). This structure is wellgdefined in coastal ecosystems. Zooplankton 11

12 biomass generally peaks during warmer months due to higher temperatures promoting phytoplankton growth, and provides appropriate spawning conditions for many species (TaylorandPearce1999;Tsikliraset'al.2010;Gilmouret'al.2016).Increasedtemperatures stimulate nutrient pulses, promoting phytoplankton blooms and zooplankton biomass (Findlayet'al.2006).Zooplanktongrazinghelpstodecreasephytoplanktonblooms,keeping nutrientlevelsdown(findlayet'al.2006).zooplanktonrespondtophytoplanktonavailability; therefore, zooplankton biomass is often positively correlated to peaks in phytoplankton abundance(kiorboeandnielsen1994;irigoienet'al.2004;batchelderet'al.2012).autumnal plankton blooms on the GBR, eastern Australia, are produced by increased nutrients, sufficientlightavailabilityandverticalmixingfromdeeperlayers(findlayet'al.2006).studies from the Sea of Japan indicate higher zooplankton abundance in warmer months, with a seasonalvariationofspeciescomposition(joet'al.2016).theberingseahasshownhigher abundanceinspring,duetoincreasedtemperaturespromotingphytoplanktongrowth,which supportszooplanktonbloomsinaprilgmay(coyleet'al.2008).localstormspromotemixing, which encourages postgbloom productivity events within the plankton(coyle et' al. 2008). Copepodspeciesmakeupahighpercentageofthezooplanktonthroughoutmanyregions (Coyleet'al.2008;Richardson2008;Joet'al.2016).Thezooplanktonspeciescompositionin theseaofjapanismostlymadeupofcopepods,chaetognaths,ostracodsandchordates(jo et'al.2016),whilecopepodsarethemostabundantzooplanktonintheberingsea(coyleet' al.2008).copepodsandothercrustaceanshaveahighernitrogenandproteincontentthan gelatinousspecies,havingapproximately68%and23%ofproteinrespectively(joet'al.2016). Due to their abundance, and high nutritional value, they are important drivers of trophic interactions(ladharet'al.2014). However, due to increased anthropogenic stressors on the marine environment such as eutrophication, overgfishing and climate change, blooms of gelatinous zooplankton (i.e. cnidarians,tunicatesandctenophores)areincreasingaroundtheworld(lynamet'al.2006; Jasperset'al.2014).Gelatinouszooplanktonhaveahighwatercontent,andgenerallyhave lownutritionalquality(jasperset'al.2014;wanget'al.2015).amonggelatinouszooplankton, 12

13 chaetognathshaveahigherlipidcontentthanctenophores,tunicatesorscyphozoans(wang et'al.2015). Organismswithinthezooplanktoncommunitywillhavevaryingdegreesofnutritionalworth atdifferentstagesoftheirlife(e.g.larvalandeggphases),resultinginseasonalvariationwith reproductionandspawningevents(guzmánet'al.2016;bascuret'al.2017).duetothehigh proteincontentofcopepodsandeuphausiids(wangandjeffs2014)theyaregenerallythe dominantspeciestargetedinplanktivorousfishgfeedingaggregations(armstronget'al.2016; Bennett et' al. 2016; McGregor pers. comm.), rather than tunicates or chaetognaths. Horizontal plankton tows conducted within the Ningaloo Marine Park during May 2013, showedthatcrustaceansdominatedtheplankton,followedbygelatinoustaxa(west2013). WhalesharksareobservedaroundNingaloofromMarchtoJuneeveryyear(Wilsonet'al. 2001) and these seasonal aggregations are believed to coincide with the nutritionally rich zooplankton available at this time (Hanson and McKinnon 2009). The zooplankton composition showed temporal variation, indicating high variability in species dynamics. Verticalplanktontowsrevealedzooplanktontobemoreabundantatnight,whenspeciesof decapod and euphausiid crustaceans vertically migrate from depth, indicating an obvious diurnalpattern(west2013).copepods,chaetognaths,salpsandeggsdidnotshowanobvious diurnaltrend,howevercontributedsignificantlytozooplanktonassemblages(west2013). 1.3.BiochemicalComposition LipidsandFattyAcids Lipidsprovidemanyimportantfunctions,suchasenergyreserves,antioxidantsandbuoyancy regulation(kattneret'al.2007).essentialfattyacidsareneededinanimaldiets,forgrowth, survival and reproductive success(mullergnavarra 2008). Polyunsaturated fatty acids(ωg3 and ωg6) are particularly important for animals as they sustain membrane fluidity and maintain tissue hormones (MullergNavarra 2008). Lipids in zooplankton have important physiologicalpropertiesforreproduction,earlydevelopmentandtimesofdormancy(kattner 13

14 et' al. 2007). By understanding how these critical nutrient levels are transferred from one trophicleveltothenext,thelipidcontentofzooplanktoncanbeusedasatrophicmarkerto determinetheproductivityofaparticularenvironment(dalsgaardet'al.2003). Lipidsareproducedbyphytoplankton,thenconsumedbyherbivorouszooplankton,which arepreyeduponbymanylargerorganisms,transferringenergyfromprimarytosecondary andtertiaryproduction(dalsgaardet'al.2003).particularfattyacidscanbetracedastheyare transferredupthefoodchain,indicatingpredatorgpreyinteractions(dalsgaardet'al.2003). Zooplanktonconsumemostoftheessentialfattyacidstheyneedforsurvival,growthand reproductionfromphytoplanktoncommunities(sternerandschulz1998),aswellasother zooplankton. Zooplankton excretion, and biomineralisation of faeces by bacteria, helps to regenerate nitrogen levels in the ocean, and encourage phytoplankton productivity (Richardson2008).Tropicalregionshaveahighturnoverofzooplanktonbiomass,resultingin lipidgpoororganisms,whichiscommonwithinoligotrophicwatersduetotheirhighmetabolic rate(kattneret'al.2007).tropicalmarineplanktondonotneedtoaccumulatelipidstoresfor timeswhenfoodisscarce,becauselowconcentrationsofpreycanbefoundyearroundin tropicalregions(barroetaet'al.2017).incomparison,zooplanktoninhighglatituderegions have large lipid stores, as they convert lipidgpoor phytoplankton into rich lipid deposits (KattnerandHagen1995).LipidcontentoffisheggsandlarvaeintheSouthEasternPacificis lowerinsummerandhigherinwinter,duetotheneedtostorelipidsduringwinterforsurvival intimesofdormancy(diapause)(bascuret'al.2017).whileseasonalvariationsintemperate regions are significantly different, they are not as apparent in the tropics; this drives the differences in lipid storage. The changing global climate could have effectsonlipidrich zooplankton, as increasing temperatures influence the stability of the water column, productivity,sizecompositionanddiversityandtrophicefficiencyofzooplankton(richardson 2008).Thiscouldpromptashiftinspeciesdominance,affectingtheenergytransferbetween producerandconsumer(kattneret'al.2007). 14

15 Copepodsgenerallyhavehighlipidcontentandarethereforeanimportantfoodresourcefor manyhighertrophicorganisms(kattneret'al.2007).lipidstoresprovideenergythroughout thecoldermonths,withsomeorganismsbeingabletoreproduceinwinterwithoutneeding tofeed(kattneret'al.2007).however,manyanimalsrelyonlipidgrichplanktonandaligntheir reproductiontoeventswithplanktonicabundance(kattneret'al.2007).calanoidcopepods are particularly rich in monounsaturated fatty acids, as they consume them from phytoplankton;thisinturnistransferredupthefoodchaintohighertrophicanimals(kattner et'al.2007),suchaswhalesharksandmantarays.therefore,thehealthofzooplanktonwill determinethehealthoftheirpredators(dalsgaardet'al.2003) Protein Proteins are responsible for a variety of physiological functions, which create the cell structureinorganisms(harriset'al.2000).theyaremadeupofhundredsofsmallerunits calledaminoacids,whichareessentialinanimalmetabolism.aminoacidchainsareformed by specific bonds and are unique to every protein (Harris et' al. 2000). There are primary structures, formed by pure amino acid chains, and secondary, tertiary and quaternary structuresformedbyspecificaminoacidbonds(harriset'al.2000).proteinsarethemajor componentincellprotoplasm(harriset'al.2000).proteinrepresentsonaverage32%ofthe cellular dry weight in phytoplankton (Moreno and Martiny 2017), and is transferred to zooplankton when consumed. The limiting nutrient (C, N or P) in a particular system determines which proteins are regulated and the organisms capacity to uptake nutrients variesbetweenplanktoniclineages(morenoandmartiny2017).variousstudieshavefound higher amounts of protein within the plankton during warmer months (Percy 1979; Monchevaet'al.2003;Verlinden2010),whichgenerallycoincideswithreproductivecycles (Percy1979). Zooplanktongenerallyconsistofbetween10g50%protein(Harriset'al.2000).Zooplanktonin polarregionsconsistofahighamountofprotein (PercyandFife1981),wherethereisan abundanceofproteinricheuphausiids(forexampleantarctickrill)andcopepods(murphyet' 15

16 al.2016).copepodscontainalargeamountofprotein,whichispresentyeargroundinthesea of Japan (~48%) (Joet' al. 2016). Zooplankton in the Southern Ocean has a high protein content(~70%),whilethoseinthearabianseahavelessprotein(~51%)butarehigherin carbohydratesandlipids(hedgeset'al.2002).proteinwasfoundtobethemajorcomponent alongthewestcoastofindia(~35%),wherehighamountsofcalanoidcopepodsandfisheggs were present(jagadeesan et' al. 2010). Tropical plankton communities can also store high amountsofproteins,buthavealowerenergeticvaluethanthoseinhighglatitudes(barroeta et' al. 2017). The zooplankton around North Stradbroke Island, Queensland contained less than 10% protein (Verlinden 2010). The differences between ocean regions indicate high variability,asdifferentspeciesstorevaryingamountsofnutrients(jasperset'al.2014) Carbohydrates Carbohydratesareadiversegroupofcompounds,thesimplestofwhicharethesugarswhich form two large groups: the oligosaccharides and polysaccharides (Harris et' al.' 2000). Carbohydratesarefoundinabundanceinphytoplanktoncellwalls,contributingover50%of theirbiochemicalcomposition(romankevich1984;joet'al.2016),however,areusuallyonly foundinsmallamounts(<10%)inzooplankton(romankevich1984;harriset'al.2000).chitin, atypeofcarbohydrate,formstheexoskeletonsofcrustaceansandconsistsofaminogsugars, aformofmucopolysaccharides(harriset'al.2000).'chitinhasnonutritionalvalue,however isaverycommonbiogpolymerwithintheocean.carbohydratesareecologicallysignificantas theyareusedtocreatenewcompoundsviametabolicprocesses(romankevich1984),are richincarbon(morenoandmartiny2017),andassistwithenergeticrequirements(ingoleand Parulekar1995). OneoftheearlierdeterminationsofcarbohydratecontentwithinzooplanktonwasbyBrandt (1898);suggestingzooplanktoncomprisingmostlyofcopepodshasacarbohydratecontent of approximately 20%, which is much higher than those found in more recent studies (Raymont and Krishnaswamy 1960; Raymont and Conover 1961; Romankevich 1984). Raymont and Krishnaswamy (1960) suggested zooplankton from the English Channel to 16

17 consistofalowamountofcarbohydrates(<5%),whichincreaseswhentheorganismsare activelyfeeding,andlowerswhenstarved.carbohydrateswithinzooplanktonassemblages aroundnorthstradbrokeislandincreaseduringspringtoapproximately15%ofdryweight, which has been attributed to local phytoplankton blooms(verlinden 2010). Carbohydrate levels of zooplankton have also been observed to increase during spring and summer in ConceptionBay,Newfoundland(Choeet'al.2003).Thiscanbeattributedtothevaryinglife stages of planktonic organisms such as maturing copepods being present during warmer months, and immature organisms during colder months, coinciding with a lower carbohydratepercentage(choeet'al.2003) Carbon:NitrogenRatio The ratio of carbon to nitrogen (C:N) within planktonic organisms influences the nutrient cyclingofmarinefoodwebs(vredeet'al.2004).thisaffectsthestructureandfunctioningof foodwebs,havingrepercussionsfororganismgrowthefficiency(vredeet'al.2004).c:nratios showsignificantinterspeciesvariation,andvarywithindifferentlifestages(vredeet'al.2004; DeLorenzoCostaet'al.2006).C:Nratiospositivelycorrespondtolipidcontent,wherefemale copepods experience less lipids after reproducing, therefore have lower C:N ratios (DeLorenzoCostaet'al.2006).HighC:Nratiostypicallycorrespondwithhighcarbonvalues andlownitrogen. Highglatitudes generally contain much higher carbon percentages than subgtropical and tropicalregionswithupto70%carbonandc:nratiosupto10(ikedaandmckinnon2011), whereastropicalregionstypicallyexperiencelowerc:nratiosofapproximately3g4and<40% organiccarbon(ikedaandmckinnon2011).tropicalzooplanktonexperienceamuchmore stableenvironmentthanthoseinpolarregions,thereforelessvariationinc:nratiosisusually found. C:N ratios have been found to generally increase during spring, where warmer temperaturespromotephytoplanktonblooms,increasingcarbonintothesystem(escribano et'al.2007;kamburskaandfondagumani2009;verlinden2010). 17

18 1.4.ImpactsofClimateChangeonPlanktonCompositionandDistribution Rising temperature due to global climate change is considered to be one of the most important factors affecting the future of marine ecosystems. Global oceanic circulation is becomingmorestratifiedduetohigherconcentrationsofatmosphericcarbondioxide(co 2 ) (Bopp et' al. 2001). Zooplankton from polar, temperate and tropical marine systems are affected by these rising CO 2 levels (Walther et' al. 2002; Smith et' al. 2016). Zooplankton abundance has been found to be less in areas with high CO 2 levels, however nutritional quality, such as fatty acid quantity is not as affected (Smith et' al. 2016). This raises the questionforfuturestudies,whetherthequalityoffoodwillbeenoughevenifthebiomassis less(smithet'al.2016). Risingtemperaturehasadirectimpactonthedeclineofphytoplanktonbiomass,whichis correlatedwithlowermesozooplanktonabundanceandrapiddeteriorationofzooplankton communities(boppet'al.2001;richardsonandschoeman2004;garzkeet'al.2015).climate changewillalsoaffectecosystemservicesprovidedbyplanktonicorganisms,suchasoxygen production, carbon sequestration and biogeochemical cycling (Richardson and Schoeman 2004).Variationsinmarineproductivityhavedirecteffectsonfishstocks,impactinghigher orderorganismsandhumanpopulationsthatrelyuponthem(boppet'al.2001). Copepodabundanceandsizehasbeenfoundtobesignificantlylessinwarmertemperatures (Garzke et' al. 2015). Mature copepods are not surviving in water bodies experiencing warming;insteadanabundanceoftheearliernaupliuslarvalstagehavebeenfound(garzke et'al.2015).thiscanbeattributedtoadeclineincopepodreproductionandanacceleration in the hatching process due to rising temperature (Garzke et' al. 2015). Increasing temperatures cause a higher daily mortality rate in copepods compared to colder environments(breteleret'al.1995).globalwarmingcouldleadtoareductioninlipidrich copepods of subarctic ecosystems, with no foreseeable prospects for replacement (Beaugrand2009;KattnerandHagen2009). 18

19 Krill(Euphausia'superba)intheSouthernOcean,akeystonespecies,supportsawidevariety ofhighertrophicanimals(waltheret'al.2002).climatechangehashaddramaticeffectson krillreproduction,impactingtheirrecruitmentbyareductioninseaiceneartheantarctic Peninsula(Waltheret'al.2002).Thedeclineinkrillrecruitmenthasnegativeconsequences onmarinefoodwebs,causingpotentialshiftsinpopulationdynamics(waltheret'al.2002). InsouthernCalifornia,macrozooplanktonabundancehasdecreasedby80%since1951,due towarmingsurfacewatersandanincreaseinthetemperaturedifferenceofthethermocline (RoemmichandMcGowan1995).Astheoceanbecomesmorestratifiedupwellingisreduced, duetothewarmingofthethermocline;upperlayersreceivelessnutrientsandmorelight, which leads to less production and a decrease in zooplankton (Roemmich and McGowan 1995). Climatechangehascausedmanyspeciestoshifttheirbiogeographyinresponsetochanges intemperature,acidity,dissolvedoxygenandnutrientavailability(bartonet'al.2016;fogarty et'al.2017).forexample,theeastaustraliancurrenttransportslarvaefromtropicalwaters tosoutherntemperatewaters,manyofwhichdonotsurviveduringwinter(fogartyet'al. 2017).However,globalwarmingcouldprovidefavourablewinterconditions,producingmore permanentpopulationsoftropicalspeciesintemperatewaters(fogartyet'al.2017).plankton communitiesinnorthamericahaveshiftedpolewardandarepredictedtocontinueshifting duetoanthropogenicinducedclimatechange(bartonet'al.2016).itispredictedthatprimary productionwilldecreaseglobally,whichwillsignificantlyalteroceanfoodwebs(steinacher et'al.2010).enhancedstratification,reducedmixing,andslowedcirculationasaconsequence of climate change decreases nutrient concentrations, which weaken the energy flows betweentrophicgroupsthatrelyuponeachotherforsurvival(steinacheret'al.2010;barton et'al.2016). Planktivoreswillbedirectlyaffectedbyashiftinplanktondistributionastheymatchtheir movementstothatoftheirprey.thechangeinzooplanktonreproductionandrecruitment 19

20 couldhavenegativeimpactsontheamountofessentialnutrientsplanktivorousfishreceive, potentiallyaffectingtheirhealth,reproductionandsurvival. 1.5.PlanktivorousElasmobranchs Planktivorousfishaggregationsappeartocoincidewithlocalseasonalevents,suchascoral spawning at Ningaloo Reef, Western Australia (Taylor 1996), copepod blooms in Mexico (Nelson and Eckert 2007), abundances of krill (Euphausia' diomedeae) in the Philippines (Rohneret'al.2017),fishspawninginBelize(Heymanet'al.2001),andplanktonicbloomsin Mozambique (Rohner et' al. 2013b). There are 14 recognised species of filter feeding elasmobranchs 11devilrayspeciesofthegenusMobula,whichincludesbothmantaray speciesmobula'birostrisandmobula'alfredi,thewhaleshark(rhincodon'typus),thebasking shark(cetorhinus'maximus)andthemegamouthshark(megachasma'pelagios),allofwhich predominantlyfeedonzooplankton(mottaet'al.2010;couturieret'al.2012;bennettet'al. 2016). InBajaCalifornia,Mexico,whalesharksareseenaggregatingtofeedonzooplanktonfrom JunetoNovember,correspondingtoanabundanceofcopepodgrichplankton(contributing upto85%ofthecompositionofthezooplankton)(nelsonandeckert2007).thereappears to be a minimum density that some large planktivorous fish require before feeding takes place,whichwasnolessthan10,000individualsm g3 (NelsonandEckert2007). Moststudiesonthedietoflargeplanktivorousfishhavebeenlimitedtoshallowandcoastal waters,howevertherearestudiesquestioningwheretheseanimalsgetthemajorityoftheir prey(bennettet'al.2016).recentstudieshavesuggestedalargeproportionoftheirdietis demersalzooplankton(couturieret'al.2013;burgesset'al.2016;rohneret'al.2017).acoustic and satellite telemetry has suggested that M.' alfredi' reside within shallow coastal regions duringtheday,butleaveatnight,posingthequestionofwheretheyspendtheirtimewhen theyleavethecoast(dewaret'al.2008;jaineet'al.2014).ithasbeensuggestedthatthey obtain the majority of their food during nightgtime (Rohner et' al. 2013a). As manta rays 20

21 appeartospendsomeoftheirtimeforagingatdepth(couturieret'al.2013;stewartet'al. 2016), when they are observed on the surface, it has been proposed they are grazing or basking,untiltheyareabletodiveagaintoforagefortherichabundanceofprey(stewartet' al.2016). Episodesofincreasedplanktonicbiomass,andfishspawningeventsintropicaloligotrophic waters, generally coincide with visiting planktivores such as manta rays and whale sharks (Rohneret'al.2013a;Bennettet'al.2016).DuringOctobergMayontheGBR,alargepulseof zooplanktonisfedintothewhitsundayislandsbystrongtidalcurrents(bennettet'al.2016). In order to maximise the benefit of these nutritional pulses, predators must match their distribution to that of their prey, making them sensitive to prey variability (Barnett and Semmens2012).GliwiczandMaszczyk(2016)foundthatavariablepreydistributionprovides planktivorous predators with greater feeding efficiency rather than a homogenous prey distribution;thiscouldbeattributedtotheamountoftimeandenergyittakestofeedwithin apulseoffood(gliwiczandmaszczyk2016) Mantarays Mantarays,familyMobulidae,arefilterfeedingplanktivoresdistributedthroughouttropical and subgtropical regions around the world (Jaine et' al. 2014). There has been increased interest in manta ray ecotourism, due to their potential to generate significant economic benefits,particularlyincoastalcommunitiesanddevelopingcountries(andersonet'al.2011; Couturieret'al.2012).Duetofishingpressuresandthelowfecundityofthesespecies,both Mobula' alfredi and Mobula' birostris have been listed as Vulnerable to Extinction on the InternationalUnionfortheConservationofNatureandNaturalResources(IUCN)RedListof ThreatenedSpecies(Marshallet'al.2011;Couturieret'al.2012).Studiesonfeedingecology are crucial in understanding where, how and when a particular species feeds, which influences their evolutionary pattern, such as speciation, and determines reproductive success,spatialecologyandnutritionalcondition(stewartet'al.2016).thisinformationcan beusedtoimplementmanagementplansfortheprotectionandconservationofvulnerable 21

22 animals. Untilrecently,thegenusManta'wasbelievedtobemonospecific,howeverareviewofthe taxonomyofthegenusshowedtherearetwodistinctspecies:manta'birostris'(marshallet' al. 2009), an oceanic migratory species, and Manta' alfredi'(krefft 1868), a predominantly tropicalspeciesfoundaroundcoralreefsandislands(couturieret'al.2011).thegenusmanta hasrecentlybeensubjecttotaxonomicreview,andthetwospeciesofmantarayhavebeen reallocatedtothegenusmobula;thetwospeciesarenowrecognisedasmobula'birostrisand Mobula'alfredi(Whiteet'al.2017).'Mobula'alfrediissmaller,withadiscwidthofupto5m (GadigandNeto2014)andcanweighupto800kg(KitchengWheeler2013),whileM.'birostris hasadiscwidthofupto6.7mandweighsupto1,400kg(dewaret'al.2008).mantaraysare filterfeeders,usingtheircephaliclobestofunnelwaterintotheirmouthsandfilterouttheir planktonicpreythroughmodifiedgillrakers(dewaret'al.2008). Mobula'birostrisareusuallyfoundfeedinginoceanicchannelsorsurfaceslicksofaplanktonic bloom(wilsonet'al.2001;dewaret'al.2008).observationsofm.'birostrisfeedingincaptivity determinedthemotivationalbehaviourbehindtheircephaliclobes(ariandcorreia2008). Whenfoodisnotpresent,thelobesarecurleduporpartiallyopenindicatingthemantahas noincentivetofeed,oris tasting thewatercolumninsearchoffood.however,whenthere isanabundanceofplanktonthemantaunfurlsitscephaliclobes,creatingascooptofunnel prey into their mouths (Ari and Correia 2008). Mobulid gill plates have adapted morphologicallytofilteroutarangeofpreysizes,fromlargereuphausiids(krill)tosmaller calanoidcopepods(stewartet'al.2016).studiesatladyelliotisland(lei),thesouthernmost coralcayofthegreatbarrierreef(gbr),haveshownreefmantarayswillonlyfeedwhen zooplanktonisataminimumpreydensitythresholdof11.2mgm g3 (Armstronget'al.2016). Thesizeandcompositionoftheplanktonwasfoundtohavenoeffectonfeedingbehaviour (Armstronget'al.2016). 22

23 ThereisminimalinformationonM.'alfredidiets,asgutcontentanalysisisethicallydifficult to obtain when dealing with a vulnerable species (Bennett et' al. 2016). However, it is understood they mainly feed on zooplankton(including copepods, chaetognaths, krill, fish larvaeandfisheggs)(couturieret'al.2013;bennettet'al.2016;rohneret'al.2017).ithas beensuggestedthatthem.'alfredifiltrationsystemhasalowerlimitforpreysize,witha minimumlengthofapproximately1mm,indicatingtheyrelyonmesozooplankton(bennett et'al.2016).speciesofthesubgclasscopepodawerefoundtodominatethegutcontentsof am.'alfredi'specimenlandedoffthewhitsundays,easternaustralia(bennettet'al.2016). Specifically,calanoidcopepodswerefoundwithinthegut,astheycontributesignificantlyto thegbrzooplanktoncomposition(saleet'al.1976;bennettet'al.2016),alongwithalarge proportionofchaetognaths(bennettet'al.2016). Planktonbecomesconcentratedalongoceanographicfronts,eddiesandupwellings,which provide important foraging opportunities for planktivorous organisms, influencing their distributionandfeedingbehaviour(jaineet'al.2014).likeotherlargeplanktivorousfish,itis believed that manta rays seek out their prey and aggregate to areas with high planktonic abundance (Anderson et' al. 2011). Many coastal regions are areas rich with plankton, generallyassociatedwithupwellingsthatverticallytransportnutrientsupfromthedepths (Parra Venegas et' al. 2011). At Ningaloo Reef, Western Australia, zooplankton becomes concentratedalongthecoast,potentiallyduetothecombinedinfluenceofoceancurrents and swell (McGregor pers. comm.). Fish and coral spawn can also create extensive slicks withinthereeflagoonfromprevailingwinds(taylorandpearce1999;mcgregorpers.comm). MantaraysareoftenseenatNingaloofeedingclosetothebeachonpatchesofplankton.In Mexico,aroundthenortheastcoastoftheYucatanPeninsula,mantarayshavebeenobserved feeding alongside other planktivorous fish (Parra Venegas et' al. 2011). These feeding aggregations have been attributed to highly productive waters from tropical coastal upwellings(parravenegaset'al.2011).offshoreplanktonoccursinlowconcentrationswhen compared to coastal areas, which would imply a less productive food source for large planktivorousfish(parravenegaset'al.2011).largecoastalaggregationsofplanktivoressuch 23

24 asmantaraysandwhalesharksareoftencorrelatedwithspawningevents(parravenegaset' al.2011).aroundtheremotepalmyraatoll,inthenorthernlineislandsofthecentralpacific Ocean,localmantaraypopulationsreceivethemajorityoftheirenergeticrequirementsfrom nutrient rich zooplankton within the atoll s lagoon, rather than offshore (McCauley et' al. 2014). BasedonlongtermmantaraysightingsatLEI,individualshavebeenfoundmostcommonly feeding approximately two hours before low tide, which coincides with times of high planktonicbiomass(armstronget'al.2016).similarly,agreaterproportionofmantarayshave been found feeding in cooler waters, where there is a higher biomass of zooplankton (Armstronget'al.2016).Mantarayshavebeenobservedlessfrequentlyinstrongercurrents compared to milder currents and more frequently during the second quarter of the lunar cycle,indicatingthattideshaveasignificantinfluenceontheincidenceofsightings(rohner et' al. 2013b). As zooplankton accumulates during high tide, they have been classified as 'activedrifters'ratherthan'passiveparticles'(wiafeandfrid1996).zooplanktondensityis oftengreatestatthethermocline,whichissupportedbystudiesofmobula'birostris 'diving behaviour.itwasfoundthattheseanimalsspendmuchoftheirtimeatdepththroughoutthe year,whichcanbedirectlyrelatedtopreydensity(stewartet'al.2016). MantaraysaroundLEIaremostcommonlyobservedinlargenumbersduringwinter,however duetoauniquesequenceofevents,thelargestrecordedmantarayfeedingaggregationin AustraliawasseenoffLEIinthesummerof2013.TropicalCycloneOswaldcausedamass influx of nutrients from river run off, upwellings, extensive eddy activity and convergent fronts,triggeringplanktonblooms(weekset'al.2015).approximately150mantarayswere seen feeding along the oceanographic front, where biological productivity is concentrated intoareasrichinnutrients,attractingaggregationsofplanktivoresandotherspecies(weeks et'al.2015). 24

25 Mobula' alfredi have a much shorter roaming distance than M.' birostris, which are more migratory.m.'alfredi'havenotbeenobservedtotraveloutsideahomerangeofapproximately 500km(Couturieret'al.2011).Deakoset'al.(2011)suggestedthatM.'alfredi'donottravel greatdistancesoverdeepwater,butaremostcommonlyfoundnearcoastalregions,suchas Komodo,Indonesia(Dewaret'al.2008),Hawaii(Deakoset'al.2011),Mozambique(Marshall et'al.2011)andningalooreef,australia(sleemanet'al.2007).asm.'alfrediremainwithina relatively small region they are heavily influenced by fluctuations in local environmental parameters (Rohner et' al. 2013b). Temperature can be a predictor of Mobula' alfredi presence: they are rarely seen in temperatures below 18 C and generally reside within tropicalsystems(rohneret'al.2013b).inmozambique,sightingsofm.'alfrediarehigherin summer,coincidingwithreproductionandbirthing(marshallandbennett2010;rohneret'al. 2013a).StudiesinMozambiquefoundtemperaturehadasignificantinfluenceonmantaray aggregations,warmerwatershavingapositiveeffect(rohneret'al.2013a),contrastingwhat wasfoundatlei(armstronget'al.2016).thisvariabilitycancomplicateanypotentialdataon aggregation trends or sightings (Rohner et' al. 2013a). Even though Mobula' alfredi are observedyearround,theyshowclearseasonalpatternsastheyfollowtheirprey(rohneret' al. 2013a). Observations off North Stradbroke Island, eastern Australia, revealed mantas visitedduringwarmermonthswhenplanktonisinhighabundance(verlinden2010). 1.6.NingalooReef NingalooReefextendsapproximately260kmalongthewestcoastofAustralia,southfrom thenorthgwestcape(sleemanet'al.2007).ningalooisafringingreefthatpartiallyencloses ashallowlagoon,andistheonlysizeablereefsystemonthewestcoastofacontinent(wilson et'al.2002).thereefisprotectedbytheningaloomarinepark,andwasrecognisedasaworld HeritageAreain2011(NingalooCoastWorldHeritageTeam2017).BatemanBayisalarge embaymentnorthofthesmallcoastaltownofcoralbay,situatedwithinthecentralpartof NingalooReef.MantarayscanbefoundwithinBatemanBayyearround,aszooplanktongets funneledintotheareaviathecardabiapassage(mcgregorpers.comm.). 25

26 ThedominantcurrentofftheWesternAustraliancoastistheLeeuwinCurrent(LC),awarm lowsalinitycurrentthatflowspoleward,sustaininglifeandcoralgrowthontheningalooreef (TaylorandPearce1999).Itsstrengthandpolewardflowsuppressesnutrientrichupwellings alongthewesternaustraliancontinentalshelf(rousseauxet'al.2012).duringautumnand winterthelcflowsatitsstrongest(rousseauxet'al.2012)andinsummer,asitweakens,the weakernorthwardflowingningaloocurrentdominates.themixedlayerdepth(mld)isa physicalparametergiventotheupperlayeroftheocean,wheretemperature,salinityand densityhavebeenfairlyhomogenisedbywind,wavesandsolarradiation.themlddeepens duringautumnasaresponsetothestrengtheningofthelc,increasingsurfacenutrientsand chlorophyllgaconcentrations(rousseauxet'al.2012).chlorophyllgaisoftenusedtomeasure the productivity of the ocean and phytoplankton abundance(sleeman et' al. 2007), which peaksduringautumnduetothemldbeingatitsdeepest(rousseauxet'al.2012). For most of the year, Bateman Bay is subject to prevailing southgeasterly trade winds throughout the night and morning until the southgwesterly sea breeze takes over each afternoon(taylorandpearce1999).eventhoughtheprevailingwindsaresoutherly,thelc isabletoovercomethemasitcontinuestoflowsouth(rousseauxet'al.2012).whenthelc weakens during summer, and the southgwesterly winds grow stronger, windgdriven local currentsdominatetheregion,flowingnorthwards.withinthelagoon,theflowisdrivenby thewindsinanortherlydirection,affectinglocaltransport. TheLCsystemfavourscoastaldownwellingduetoitspolewardflowalongsidetheNingaloo boundary current(zhang et' al. 2016), which negatively affects coastal nutrient levels and productivity (Hanson et' al. 2005). The LC has a significant influence on the transport of organismsandbiologicalactivity(taylorandpearce1999).thecurrentflowsmostweaklyat theningaloopeninsula,wherethereareepisodicsoutherlywindsstrongenoughtochange thedirectionofthealonggshelfcurrent(fromsouthwardtonorthward)generatingtransient coastalupwelling,promotingplanktonblooms(zhanget'al.2016).thecontinentalshelfalong theningaloocoastissteeperthanmostshelveswithaneasternboundarycurrentsystem(i.e. 26

27 Peru, Benguela, California and Northwest Africa) (Chavez and Messié 2009; Pitcher et' al. 2010; Zhang et' al. 2016), meaning any upwellings generally come from the middle of the watercolumnratherthanclosertotheseagbed(xuet'al.2016;zhanget'al.2016).thesupply ofnutrientstotheningaloosystemismostlikelyfromdeeperlayersmixingintothesurface waters,astherearefewriverinputs(rousseauxet'al.2012).duetothetransientnatureof theseupwellingepisodes,thebenthiccoralgrowthisabletothrivebecausenutrientsare limited and temperature stresses are controlled (Zhang et' al. 2016). Fluctuations in the strengthofthelcinfluencetheproductionanddistributionofplanktonyearround(sleeman et'al.2007).wavesfromtheouterreefbringinrichlyoxygenatedwaters,whichflowback outviagapsinthereefcrest,creatingawellgmixedsystemthatsupportsadiversearrayof organisms(taylorandpearce1999;sleemanet'al.2007). During autumn, high concentrations of surface nutrients and chlorophyllga have been measured,whichdriveplanktonicbloomsatthistimeofyear(rousseauxet'al.2012).itis believedthereisaninfluxofnitrogentotheningaloosystemduringthistime,whichiscaused byacombinationofcoolingsurfacewatersandtheaccelerationofthelc,causingnutrients fromdeepwatertomixwiththeupperlayersofthewatercolumn(rousseauxet'al.2012). The combination of the warm LC and cooling surface waters causes the thermocline to breakdown,promotingmixing(priceet'al.1986). DuringsummeranantigclockwiseeddyhasbeenobservedformingofftheLC,southofPoint Cloates,whichhasimportantimplicationsfororganismssuchaszooplanktonandcoralspawn (TaylorandPearce1999).Theeddyhasthepotentialtotransportandmixbiotafromnorthern NingalooReef,acrossthecontinentalshelfandbackintothelagoonareaviatheNingaloo Current(TaylorandPearce1999).ThiscountergcurrentisstrongestduringMarchandApril, which is peak coral spawning time (Taylor and Pearce 1999). Eddies are recognised as importantforoligotrophicwaters,astheyincreaseproductivityandnutrientsintheregion (LebourgesgDhaussyet'al.2014).Theupwellinginthecentreofcycloniceddiestransports nutrientgrich waters into the euphotic zone (LebourgesgDhaussy et' al. 2014).Theeddy 27

28 observed off the LC is antigcyclonic (Taylor and Pearce 1999), which causes central downwelling,butconcentratesmaterialatthesurface(bakun2006).zooplanktonbiomass hasbeenobservedtobehigherincycloniceddies,asopposedtoantigcyclonicones,under stableconditions(lebourgesgdhaussyet'al.2014).ithasbeensuggestedthattheningaloo Current transports large amounts of protein from coral spawn and larvae throughout the Ningaloosystemduringthistimeofyear,whichisimportantforthereef ssurvival(taylorand Pearce1999).Manyotherorganismshavebeenobservedtospawnatasimilartime,which boostsproteincontentwithinthezooplanktonasmillionsofeggsaredispersed(taylorand Pearce 1999). The Ningaloo Current is predominantly driven by the southerly winds, and thereforeislimitedtosurfacewaters;however,itisstrongenoughtogeneratecoldwater upwellings,enhancingplanktonicproductivityandbiomass(wooet'al.2006;sleemanet'al. 2007). WhalesharksaggregatetoNingalooReefbetweenMarchandJuneeveryyear(Wilsonet'al. 2001;Sleemanet'al.2007).Theirarrivalisbelievedtocoincidewithzooplanktonproductivity events,suchasfishandcoralspawning,whichpromoteplanktonproduction(sleemanet'al. 2010).Thisalsocorrespondswithlargeoffshoreschoolsofkrillandfishthattraveldownfrom northernningaloo(sleemanet'al.2007).thestrengthofthelcisdependentontheelniño SouthernOscillation(ENSO),whichdescribesthechangeinatmosphericpressuregradient betweenthecentralpacificandnortheasternindianocean(wilsonet'al.2001).whenthe pressureishigheroverthepacificoceanthantheindian,theleeuwincurrentisstronger, duetoariseinsealevelaroundindonesia,wheretheindonesianthroughgflowpusheswarm waterdownthewestaustraliancoast.wilsonet'al.(2001)foundthatensocorrelatedwith whale shark aggregations off Ningaloo, suggesting their movements are influenced by fluctuationsinthelc sstrength.thelcprovidesdirectionalcuesandisamethodofactive transportformanylargemigratoryanimals(sleemanet'al.2007). Manta ray abundance and distribution has been attributed to oceanographic bottom up processesthatinfluencefoodavailability(sleemanet'al.2007).variablessuchasbathymetry, 28

29 sea surface temperature (Couturier et' al. 2011), and cholorophyllga concentrations have shown correlations in zooplankton distribution and abundance (Sleeman et' al. 2007). It followsthatzooplanktoncangoverntheabundanceanddistributionofplanktivorousfish. Zooplanktonabundancehasbeenusedasasurrogatemeasurementtodeterminemegafauna distribution (Sleeman et' al. 2007). As manta rays target these pockets of zooplankton abundance, whether they are present or not could be an indicator of seasonal ecosystem health(mcgregorpers.comm.).fromthiswecangaugehowwelltheningaloosystemcan supportlargeplanktivorousfish. MantaraysoccurintheNingaloowatersyearround,howeverhavebeenobservedtobemost abundantinmay(mcgregorpers.comm.).morethan800individualshavebeenidentified fromthebatemanbayregion,someremainingallyearround,whileothersareseenmore sporadically(mcgregorpers.comm.).unlikeotherplanktivores,bothmantarayspecieshave shown patterns of residency in their home regions such as, Indonesia, Mozambique, Philippines,Mexico(Stewartet'al.2016)andAustralia(Armstronget'al.2016;McGregorpers. comm).gelatinousspecieshavebeenobservedinabundanceatningalooduringwinter,so nutritionalquantitycanbeexpectedtobeloweratthistime,whichcorrespondswithfewer observed manta ray feeding aggregations (McGregor pers. comm.). Copepods and chaetognaths dominate the zooplankton communities during warmer temperatures, coinciding with frequent manta ray sightings (McGregor pers. comm.). Measuring the availablebiochemicalcompositionofpreyitemshelpsusunderstandhowmuchnutritionthe animals within a certain region are receiving. Preliminary research on zooplankton distributionandspeciescompositionhasbeenusedasaguidetodeterminewhereandwhen seasonalzooplanktonaggregationsmayoccur. 1.7.Aims Thefocusofthisstudyisonthecompositionandvariabilityofmesozooplankton(300µm 1000 µm) communities within Bateman Bay, Ningaloo Reef. The aim is to quantify the nutritional value (lipid, protein and carbohydrates) these zooplankton populations are 29

30 providingtoplanktivorousfishsuchasmantarays.thisresearchaimstoaddtopreliminary work done on zooplankton distribution and composition, by investigating the seasonal nutritionalquality.itishypothesisedthatzooplanktonnutritionalquantitywillbehigherin autumn,whenanabundanceofnutritionallyrichorganismsisfound. 30

31 2.MaterialsandMethods 2.1.DescriptionofStudyArea Bateman'Bay' Bateman Bay ( S, E) is a large north facing embayment, situated betweenpointmaudandbruboodjoopoint,withintheningalooreefmarinepark(figure1). Figure1.BatemanBay,NingalooReef.MapofNingalooMarinePark(indicatedleft,bygreenboxed area)alongthenorthwestcape,showingthecoralbayregion(insetleft),andmapofbatemanbay (zoomedright),showingmantarayaggregationareasusedfortheautumn(black),andwinter(green) samplesites.blueshadedareaindicatestheningalooreefcrest. BatemanBayissemigenclosedandisapproximately5kmwide,fromthecoastlinetothereef crest.unlikeothershelteredlagoonareasalongtheningalooreef,batemanbayisopento 31