3 2 1 Cowen andSponaugle2009). the affect all can flows ocean of et al.2008, (Siegel destination to aparticular from asourceisland be transported will that larvae probability nature turbulent the from arising chance random even and capabilities, populations, timingof spawning, duration of the larval period,dailymortalityrates, sensory andswimming necessary to understand howaspects of the larvae themselvescanaffect their transport.Sizeof source of theoceancurrents bywhichlarvaearetransported.It stand thespeed,direction,andseasonality is also A varietyoffactors canaffectit isnecessarytounder thetransport oflarvaeamongislands.Mostobviously ecosystem (Botsfordetal.2009,Christie2010, Costelloetal.2010). the broader the roleofprotectedareas inmaintaining to understand network sitesshouldbeconsidered at produced the fatesoflarvae events.Inaddition, disturbance between sites cansuccessfullyrepopulate network that such appropriately spaced and protected be must sources larval Sufficient 2009). al. et Planes of larvaltransport(Gainesetal.2003,ShanksBotsford dent uponanunderstanding al. 2009, network ofMPAsning aregional is depen to disturbance,whethernaturaloranthropogenic, thatareresilient clear thatplan Jones etal.2009,McCookSteneckSale2010).Ithasbecome There hasbeena recent proliferationof studies onreef connectivity andMPA resilience (Almanyet al. 2009, ishment throughouttheregionalecosystem. replen- Samoan reefecosystems,andthecontributionofreefstopopulation larvae formaintaining ocean currents in and around the archipelago and discusses their potential influence on important sources of 2009,Costelloetal.2010). 2007, CowenandSponaugle of characterization This chapterprovidesadetailed goals (Gainesetal. planning and conservation management is necessarytoachieve via larvalexchange agement efforts are focusedonparticularsites within theinformationonconnectivitypatterns archipelago, 2007, Christieetal.2010).Evenwhenman- et al. (Gaines at otherlocations made sions on deci- is intricatelylinkedtoanddependent ment of each placeinthe Samoan Archipelago that theecology,manage and conservation, isimportantbecauseitmeans larval transport that resultsfrom ity amongislandpopulations some portionof their larvallife. The connectiv currents foratleast ject totransportbyocean and adiversityofotherfaunathat are sub- starfish crown-of-thorns worms, giant palolo clams, corals, spawning broadcast fish, bony posses apelagiclarvalphase. This includes inhabit thecoralreefecosystems of the region ard 2008). Many of the marine organismsthat and seamounts inthe region (CraigandBrain- larvae ofmarinebiotatoandfromtheislands the oceancurrentswhichcarryeggsand the Samoan is Archipelago shapedinpartby The biogeogr I ContractNo. DG133C07NC0616 nt Seamounts oftheSamoan Archipelago and Adjacent IslandNations NOAA/NOS/NCCOS/CCMA Coastal Oceanographic Assessment Statusand Trends Branch NOAA/NOS/NCCOS/CCMA/Biogeography BranchandConsolidatedSafetyServices,Inc., Fairfax,VA, underNOAA NOAA/NOS/NCCOS/CCMA BiogeographyBranch Ocean CurrentsandLarvalTransport Among IslandsandShallow r o du ction aphy of coral reef ecosystems in of coral aphy Matthew S.Kendall 1 , MatthewPoti 2 , TimothyWynne - - Photo credit:PeterCraig,NPS. Image 8.MassrecruitmenteventofCtenochaetusstriatus 3 , BrianP. Kinlan 2 andLaurieB.Bauer 2 . - - - page 27 Chapter 3 - Currents and Larval Connectivity page 28 Chapter 3 - Currents and Larval Connectivity American Samoa. Greenlinesdenotesources fromSamoa.Blacklinesdenote allothersources. Dotted linesdenote separate islands,seamounts, or island groups clustered for analysis. Redlinesdenote larvalsourcesfrom Figure 3.1.Samoan model. bythe9kmgridcellsofHYCOMhydrodynamic depicted islands andsurrounding Archipelago transport simulationsofvirtuallarvaefromathree-dimensionalhydrodynamicmodel. nections amongislandsand shallow seamounts:observationaloceancurrentdata from passive drifters and connectivity (Figure3.1). regional Two primarytechniqueswereusedto quantify currentsandlarvalcon- of island nations surrounding Tokelau, westernCookIslands,Niue, Tonga, andWallis Islandtounderstand The studyregion Me dispersal inathree-dimensionalregionaloceanmodel. Toof larval data onoceancurrentswithsimulations observational achievethesegoals,wehavecombined longevity, larval daily mortalityrate)onthoseconnections. (e.g. characteristics history life larval of combinations various of influence the Quantify 4. 3. Identifykeysourcesanddestinationsoflarvaeforeachisland,and, 2. Modelthepotentialtransportpathwaysofvirtuallarvaeamongislandsourcesthroughoutregion, 1. QuantifyanddescriberegionaloceancurrentsintheSamoan Archipelago, The goalsofthischapterwereto: t h o d s was centered on the islands and seamounts of theSamoan and seamounts on theislands was centered but alsoincluded Archipelago drifters observations that fell completely within a given season, region, and ENSO year prevented use ofthe and ENSOyear prevented season, region, a given within that fell completely drifters observations in the Counter Current)andusedas responsevariables or SouthEquatorial ANOVAs. The lownumberof Current (South Equatorial for eachdrifterbyseason,ENSOstatus, andregion calculated were mean speed sources of variability incurrentsamongseasons,years,and positionsinthestudyarea.Medianbearingand and differences significant the understand to histograms and comparisons, means multiple ANOVA,using evaluated were distance transport and speed, heading, drifter on variables these of summer.influence The the Counter Currentduring 9º Sand12ºbytheSouthEquatorial but isinterruptedinthelatitudes between for theregion. major currentsdescribed the region Current occursallyearthroughout The SouthEquatorial based of the in thestudyarearelative tothetypicalposition Index, and3)byposition on theSouthernOscillation 2007) and 2006, (2004, years neutral or (2008), Niña La (2005), Niño El 2) simplicity, for excluded months with transition seasons or summer(December-March) 1) winter(June-August) groupings, several speedandpotentialtransportdistance.For current heading, this analysis,drifterdatawerecategorizedinto determine the influence of season, El Niño/Southern Oscillation (ENSO), and region within the study area on accuracy.model check month/year toqualitatively same to separately analyzed drifter datawere Inaddition, the to drifterpaths (e.g.Figure3.4)during compared current vectors(e.g.Figures3.2-3.3)werevisually lution weresuitablefor this purpose andshowedgradualtransitionsinthe major currentpatterns. Modeled Monthly vectorplotsatthisspatialreso- current vectorsfor2004to2009wereplottedat~36kmresolution. ToHYCOM monthly average currents intheregion, patterns inocean and interannual describeseasonal General CurrentPatterns to thetracksofdrifterspresentinstudyarea(216total)duringcorrespondingmonth/year. compared visually and plotted year were model current vectorsforevery monthly average timescales, longer year (2004)(e.g.Rudorff chosen model a randomly et al. 2009). Tocurrent vectorson the modeled evaluate during drifter dates/positions chosen randomly at100 regression linear velocities using model corresponding escales. Toto the were compared drifter velocities longitudinal and current vectors,latitudinal daily evaluate Modeled currentsfrom HYCOM werevalidatedbycomparingthemwithdrifterdataondailyandmonthlytim- H Samoan reefecosystems. of connectivity the impact may literature scientific the in reported rates mortality and capabilities, swimming cies. Weperiods, of larvaldurations,precompetency how awiderangeofcombinations insteadexamined spe- of aparticular model parametersforthelifehistoryandbehaviors (Leis 2007)ratherthanspecifying to affectthe potential that have parameters of model a range to evaluate was approach general dispersal Our parameters. realistic with larvae fish and coral virtual of connectivity interisland model to then and area study the around and in currents the describe to used first were model hydrodynamic and data drifter The larval movement. with nullcurrent vectors (blackcellsinFigure3.1). These nullcellswereusedasa land mask and blocked evaluate broaderscalesoflarvaltransportamongislands.IslandsarerepresentedinHYCOMasgridcells vection currentsvery close to shore (Sweareret al. 1999, Harlanet al. 2002) andwethereforeusedit only to consortium (http://opendap.org/download). HYCOM The 9 the km model from resolution is downloaded not sufficient were to capture data localized eddy vector and con- Current fish. reef and invertebrates corals, of used tomapthecurrentsinstudyareaandmodelmovementofpassiveparticlesor“virtuallarvae” in thestudy area. 2004-2009 the period The surface/mixedlayerofHYCOM(surfaceto~10mdepth)was for cell size),a1daytimestep,andisavailable 9 bykmgrid (approximately of 1/12degree resolution et and Boudra1981,BleckBenjamin1993,Halliwell al.1998,Christieet al. 2010)withahorizontal (Bleck model hydrodynamic (HYCOM) isathreedimensional Model Oceanographic Coordinate The Hybrid larval transport. for modeling parameters select realistic and model, truth thecurrentvectorsofhydrodynamic ground a detailedrecordof actual surfacecurrents. These datawereusedto describe patternsof surface currents, arerecordedeverysixhoursandprovide Surface DrifterProgram2010).position,speed, andheading at 15mdepth(NOAAployed [CRED], NOAA CoralReefEcosystemDivision GlobalDrifterProgram[GDP]- The NOAA Global DrifterProgramusessatellitesto track an extensivearrayof passively driftingdroguesde- YCOM Validation page 29 Chapter 3 - Currents and Larval Connectivity page 30 Chapter 3 - Currents and Larval Connectivity 2006, 2008,and 2009. Average currentvectorsfor April 2009. Figure 3.3. Tonga Trench Eddy. This clockwiseeddyformedin September throughDecember of and 12S. February 2004. The South EquatorialCounterCurrentis evident as eastward vectors between 10 current vectors. of regional Figure 3.2.Example Averagesurface currentvectorsfromHYCOMfor Figure September current eastward surface Th Figure

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that couldbe “spawned”orstartedmoving insimulationsby HYCOM currentsonany datespecified. area ofreefhabitat to potential scaled larvae of virtual number reasonable but computationally a verylarge depth between0and150 m, was assignedatotalof3000 larvae(30%of 10,000) (Figure3.1). This provided and 150m. For example,acellcomprised of 50% land, 20% water deeperthan150m, and 30% waterwith This numberoflarvaewas thenadjustedbasedontheproportionof the cellwithbottomdepthsbetween 0 et al. 2010). Initially, a set of 10,000 larvae wereplacedrandomlywithineachcoastal gridcellinHYCOM. Ecosystems 2010,Bare Coral in thearea(Mesophotic reef communities its ofbothphoticandmeso-photic This was defined as the area from shore to the 150 m isobath and was based on the approximate depth lim- wasscaledto Larval production the area of the insular shelf (or seamount) withpotential coralreef habitat. the studyareawestwardtowardFiji. quickly leave thatmostlarvaefromfartheroutwould indicated analysis as larvalsourcessincepreliminary extent ofthe in thenorthern Only islands Tongaof theWallisand easternportion chain were included chain of theresultsonSamoan the edgesofstudyregiontosimplifyandfocus presentation Archipelago. Appendix at especially groups into larger were aggregated very close together A). Islandsandseamounts Virtual larvaewerestartedat each of seamounts inthestudyarea(Figure3.1; 20 island groupsandshallow Larval Sources path (sumsofallsegmentsrecordedeverysixhours). points of a drifter after a specific number of days whereas gross displacement is the total length of the drifters as means and histograms. Net displacement is simply the straight-line distancebetween the start and end for 10,20,30,50,and100daysrespectively,for alldriftersinthestudyareathatwereatlarge andplotted multi-way ANOVA fortransportdistance.Instead,grossandnetdistanceswerecalculated analysis 20°S 15°S 10°S Figure 3.4. Exampleoftypicaldrifterpaths.January2007driftersshown(NOAA Global DrifterProgram). ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! !! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! !! ! ! ! ! ! !! ! ! ! ! ! ! 175°W ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! !!! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! !! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! !! ! ! ! ! ! ! ! ! ! ! !!!! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! !!! ! ! ! ! !! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! !! ! ! ! ! ! ! ! ! ! ! ! ! ! !! ! ! ! ! ! ! ! ! ! ! ! ! !! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! !! ! ! ! ! ! !!! ! ! ! ! ! ! ! ! ! ! ! !! ! ! ! ! ! !! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! !! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! !! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! !! !! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! !! !! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! !! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! !! ! ! ! ! ! ! ! ! ! !!! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! !! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! !!! ! ! ! ! ! ! ! ! !! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! !! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! 170°W ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! !! ! !! ! ! !!! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! !! !! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! !! ! ! ! ! ! ! ! !! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! !!!!! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! !! ! ! ! ! ! ! ! !! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! !! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! !! ! ! ! ! ! !! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! 165°W ! ! ! ! !! ! ! ! ! ! ! !! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! !! ! ! ! ! ! ! ! !! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! !! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! !! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! !! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! !! ! ! ! !! ! ! ! ! ! ! ! ! etEast West Drifter Bearing South North ! ! ! ! F 160°W page 31 Chapter 3 - Currents and Larval Connectivity page 32 Chapter 3 - Currents and Larval Connectivity tion that reflects variation in drift. Using only 10% uncertainty rarely produced a probability cloud of the 1000 that ment whilerecognizing agivendrifter represents onlyone possibletrackoutof a widepotential distribu error values(10-50%)in currentvectors. agree Model pathswere comparedtoeachdrifterpathforgeneral of random a range using performed were larvae 1000 using runs model drift, separate particle in of variability of model years wereloadedintoHYCOM as starting pointsfor particle drift. To identify anappropriatelevel = 13 NOAA CRED, n= 45 NOAA GDP) met this criterion. The start date and positionof drifters from a subset from thesefeatures. of transportpathsoriginating variability was toevaluate the goal A totalof58drifters(n drifters. Only driftersegmentsthat begannearislands(within~30km) were usedforthisanalysisbecause byHYCOMfor at pared tothepathspredicted virtual larvaeoriginatingthesamedateandlocationas To levelofdiffusion/uncertainty, identify anappropriate actual drifterpaths trackedbysatellitewerecom- higher probabilityofoccurrencebutalsoregions withfewerlarvaethatindicatelessprobablelarvalpaths. cell. grid at thesamedateand paths with along occurring with morelarvae density variable has The cloud start all larvae when even pathways of potential a cloud results in transport or uncertaintytolarval ability to vectorsateachtimestepfor amorestochasticpath. random variabilitytobeapplied random vari- Adding amount of a controlled of larvalpaththatassumesnoerrorincurrentvectors andalsoenables calculation and Booth2008, Treml etal.2008,Rudorff“best guess” both adeterministic etal.2009).GNOMEprovides 2006, Chiswell et al.2003,Kobayashi et al.2000,Siegel et al.1999,Cowen connectivity studies(Polovina Diffusionis animportantaspectof from thesamelocation paths originating in larval variability orrandom eral NOAAEnvironment (GNOME Modeling v1.3.0)wasusedto tracklarvaeforallsimulations. Operational Gen- The cell. grid and date that for HYCOM from vectors current corresponding the by specified distance Virtual larvae beganat random locationswithineachcoastalgridcellandweremovedinthe direction and Larval Transport andModel region ofthestronglyseasonalSouthEquatorialCounterCurrentdescribedbelow. start for with year-roundspawning,additionaldatesandmodelingwouldberequired,especiallyislands inthe lar transportpatternstothosereportedhere.However, connectivity associated to evaluatetheinter-island Acanthurus lineatus surgeonfish the 1998). species, (Craig in fisheries Samoa species important American fish locally several A for has beenobserved spawning event, yearround mass spawning to the October-November In addition time-scales ofvariationinoceancurrentpatternswithintheregion. among various phases of the moon, a finding similar to other studies (James et al. 2002) and consistent with not differ substantiallywhen start dates wereonsuccessivedaysorevenseparatedbyasmuchamonth October andNovember. However, of evaluations themodelindicatedthat preliminary transportpatternsdid successive fullmoonsin that canoccuracrossseveraldaysorevenfollowing is recognizedsomespawning 11October 2005, 23 2004, 3 November were It 20 October2008. and 2007, 1 November 2006, November for each model year were identified as six days after the first full moon to occur after October 12. These dates and Green1996). Starting dates event forcoralwasthefocusofoursimulations. mass spawning This annual event andhasawelldocumentedlunartimingintheSamoan spawning a synchronous (Mundy Archipelago viridis worm, Eunice Palolo as acueforharvestoftheedible and Buckley1988,Mildner1991,MundyGreen1996). The presenceofslicksisused coral spawning Itano 1987, (Mildner November October orearly late either in moons after thefull nights 5-7 to spawn served Many coralspeciesandotherorganismsinIndependent American SamoaandnearbyFijihavebeenob- Mass spawningeventsandstartdatesoflarvaltransport be studiedusingmodelswithgreaterspatialresolution. drains the reef flat (Craig 1998). Such localized currents are not included at the scale of HYCOM and should al. 2011) and spawning can often be observed in reef channels where water flows in a seaward direction as it et (Ochavillo strong currentsarefound where headlands and on points are mostabundant Samoa American in fish surgeon Mature spawning. broadcast to conducive habitats in themselves position and surface the toward reefs from away rush” “spawning vertical a exhibit species fish many example, For predators. based reef avoid to coasts from away rapidly larvae and eggs sweep currents where areas to move species, fish here and,inthecaseofsome on thereefasmodeled positions at random Fish andcoralsdonotspawn , has peakspawninginNovember-January(Craiget al. 1997) whichwouldresultinsimi- U ncertainty , (Craig 2009) which is also known to engage in to engage known is also which 2009) , (Craig - - the range of PLDs expected for a wide variety of the fish and coral species of the Samoan the and of Archipelago species coral and fish the of variety wide a for expected PLDs of range the to beconsidered. Weclimate change) PLDs of10,20,30, 50,and100dayswhich encompasses evaluated This enablesavarietyof PLDs(andchanges to species andtheircorresponding PLD dueto factors such as Rather than modeling particular species with specific life history parameters, we used a wide range of PLDs. potentially shorterdispersal distances. overall, makingit important to simulate connectivity overarangeof PLD values andshift predictions toward PLDs shorten to serve may factors these of 2009). All al. et Munday 1998, Harrison and (Wilson efficiency swimming larval increase even and behaviors, reef seeking earlier of manyspecies,cause development Also ofnote,climatechangeandtheassociated riseinseasurfacetemperaturesmayacceleratelarval avoid extensiveoffshore transport(Sweareretal.1999,Harlan2002,Paris2007). to eddies coastal into entrainment and 2003), Carson-Ewart and (Leis phase larval of their for someportion habitat isencountered(McCormick1999,Richmond 1985),directedswimmingfaster than ambientcurrents until asuitable metamorphosis or partlyreversing such asdelaying mechanisms through various plankton and (McCormick their competenttimeinthe can shortenorlengthen larvae et al.2009).Inaddition, 1995, Munday Molony habitat settlement suitable of availability and temperature water as such influences with 1998, McCormick1999,Junkeretal.2006) (Wilson andHarrison in PLDaswell variability be considerable there can 2006, Junkeretal.Graham2008).Withinspecies 2000, Blanco-Martin me andPlanes or months(e.g.Bonhom days, weeks, be hours, and can genus the same within even reef organisms coral among settlement habitatorenergysource.PLDisquitevaried the endoftheirPLDiftheylackasuitable at in theplankton die simply larvae species, currents. Formany by ocean to transport are susceptible larvae Pelagic larval duration (PLD) is defined as the period of development spent in the water column during which Pelagic Larval of 60%theirPelagicLarvalDuration(seenextsection)wascompleted. from settlementuntilaminimum prevented studywere in thepresent larvae virtual period, this developmental 1998,MillerandMundy2003,Grahametal.2008,Jones2009). 1984, WilsonandHarrison To simulate et al. (Harrison somewhat morevariable andappear are lessknown competency periodsforcorallarvae in Victorfrom values 1986, Thresher etal.1989,Wellingtonand Victor 1989,andJunkeretal.2006).Pre- (calculated has elapsed Duration) Larval (see nextsection:Pelagic lifespan of their maximumlarval 60-90% to settleonce begin that individuals it isevident sizes areavailable sample reasonable for which species fish reef of variety wide a For old). days 21 to 14 at otoliths on recorded marks settlement (e.g. ages larval of overarange cies, settlementisdocumented spe- fish reef many For settlement. of capable form a body to achieving phase prior planktonic competency isthetermusedtodescribe as spend sometimedevelopingplankton.Pre- must instead and habitat suitable encounter settle evenifthey immediately larvae cannot gametes, fertilizedeggsandyoung Spawned Precompetency in larvaltransport. step to reflect this realistic level of randomness random errorincurrentvectorsateachtime using 50% quent modelrunswereconducted likely, but stillpossible,pathways. All subse- less had greaterdensity)whilealsodepicting more frequently tracks (thoseoccurring likely of more larval pathwayswhich highlighted clouds reasonable provided drifter tracksand Using 50% uncertaintynearlyalwaysencompassed paths. drifter the included that larvae D uration Photo credit:PeterCraig,NPS. Image 9.A.guttatusspawningaggregationsatdusk. - page 33 Chapter 3 - Currents and Larval Connectivity page 34 Chapter 3 - Currents and Larval Connectivity were 46%. if dailymortality were3%,19would remain if mortality were 18%,andlessthan 1wouldremainifmortality for every 1000 larvaeproducedat a source, after 20 daysinthe plankton, approximately 544wouldremain with. Forexample, to begin larvae many produce that don’t or seamounts islands for small habitat, especially of 18%. per daywithamode settlement to reaching prior die will that mostlarvae At theseratesitisclear et al. (2000) reported a wide range of mortality estimates for fish larvae of 42 species ranging from 3 to 46% time periods. Daily mortality rates are lengthy affected by and environmental distances conditions and long can vary over significantly. especially transport Cowen successful on effect significant a has mortality Larval Mortality fected. We thereforedisplayresultsforonlythe18kmsettlementzonein thisreport. rates weresomewhataffected bybufferunaf- distance,thespatialpatternsofconnectivitywererelatively considered to have successfullysettled at that island. Preliminary analysisrevealedthat, while settlement into anisland’spassed settlement zone.Ifalarvae it was period settlementzoneafteritsprecompetency as a seamounts andwasdesignated andshallow reefsaroundallislands depth contourformesophotic potential sensoryandswimmingcapabilities. A bufferusing themaximum ofeachdistancewascalculated and spectrum oforganisms a wide of thecoastalgridcellsinHYCOM),18km,and36kmtoaccommodate In this study, we investigatedarangeof9km(theresolution potential settlementzonedistancesincluding (Lugo-Fernández etal.2001,James2002,Cowen2006,ChiswellandBooth2008). investigation under on thespecies from 1to>100kmdepending ranging this “settlement zone” represent and swimtothesettlementhabitat.Consequently,have usedbuffers recentresearchers to islands around island and instead need simply to come within a “settlement zone” sufficiently close such that they can sense it is clear that larvae neednot rely exclusivelyonpassivetransportincurrentsto arrive preciselyat a distant towards reefsandtheeffectivenessagainst ambientcurrentsaretopicsofactivedebate, ofthisorientation which the larvae could detect the reef. Although the precise distance at which fish larvae can beginto orient directed towardareefbeyondthesensoryzonein 2002), althoughthisswimmingcouldnotbeintentionally that some reef fish larvae can swim impressive distances on the range of 10-50 km (Atema et al. 2002, Leis vertically inthewatercolumntoincreasetheirchancesof reaching settlementhabitat.Recentstudiesshow distances of several kilometers(Atemaetor al. 2002,Leis2006)and orienttheirmovementshorizontally at habitat settlement appropriate from plumes odor sense probably can fish Larval 2006). Leis 2005, Fisher 2003, and Carson-Ewart currents (Leis particles inocean passive cient toovercometheirtreatmentasmerely as 50% of their larval phase, some fish larvae may be capable of sustained directional swimming that is suffi- in (Leis2002,2006,Gerlachetal.2007,Leis2007,).Forasmuch the ambientcurrentstheyareembedded moving towardreefsorsimplyout-swimming fields current into migrations vertical including settlement habitats help themreachdesirable tance awayandperformbehaviorsthat can Fish larvae can sense the reef from some dis- Buffer for‘SettlementZones’ land currentsstudiedhere. to theinteris- subjected never are and hours) cies haveveryshortlarvalperiod(minutesor for suchlongperiods. Also ofnote,somespe- accuracy have reduced trajectories probably the study area after 100 days, and modeled revealed that many trackedparticleshadleft et al. 2008); however, preliminary analyses >200 daysforsomecoralspecies,Graham (e.g. ispossible longevity planktonic Longer 2006, Grahamet al. 2008, Jones et al. 2009). in BonhommeandPlanes2000,Blanco-Martin adjacent islandnations(e.g.summarytables dusk. Photocredit:PeterCraig,NPS. Image 10. A. triostegus spawning aggregations at aggregations andA.guttatusspawning 3.1). Overall transport throughout the transport throughout 3.1). Overall 3.5-3.6, the studyarea (Figures Table fected byseasonand region within af- significantly are headings current of drifterdataindicatedthat analyses The multiway ANOVAs andhistogram distance Drifter heading, speedandtransport transport processesinthestudyarea. of actual representation a reasonable current vectorsfromHYCOMare eled mod- the that indicate findings These comparisons. to drifterpathsinvisual correspondence general showed good current vectorsfromHYCOM Monthly directions basedonlinearregression. (p <0.0001) 0.0001) andlatitudinal (p < in both thelongitudinal related dates/positions werepositivelycor- el velocitiesatchosen 100 randomly (monthly) timescales.Drifterandmod- paths onbothshort (daily) andlong drifter to actual correspondence good vectors fromHYCOMshowed Current H R sources anddestinationsbylocation. location ison outside larvalsourcesfor each PLDanddailymortality rate, and bargraphsshowinglarval each and howreliant retention larval that display graphs by PLD,threedimensional distribution plots oflarval of using acombination individually wascharacterized larval sourceanddestination.Eachisland/seamount Each of the islands andshallowseamountswithinthe Samoan was examinedindetailasa Archipelago a resultoflargedifferences inthesizeofreefpopulations. the pathways, withoutconsideringvariationinnumberof larvae producedat each sourcethat could occuras transport in thiswaydepictsthepatternoflarval calculated mortality rate.Notethatconnectivity and daily eral sourcesto travel to the same destination.Separatematricesareprovidedfor each combinationof PLD row. cansumto Columns >100%, becauseit is possiblefor a highproportionof the larvaeproducedat sev- minus thesumofeach to 100% in ourstudy)isequal do notsuccessfullysettleatanyoneofthedestinations given destination(columns). Rowsthussumto a number<= 100%. The fractionof larvae that are lost(that over all5 model years. Matrix cells denotethe proportion of larvae from each source(rows)that arrived at a larvae releasedat each sourcelocationthat travelled to each of the possible destinationlocations,cumulated connectivity matricesasdestinations.ForeachPLDandmortalityrate,wecountedthenumberofsimulated the Tonga andwesternWallisin the sources butwerestillshown as larval were notmodeled Islandchains larvae trackedinthestudy.the virtual of all destinations mount sourcesand part of Islandsinthesouthern island/sea the display that matrices connectivity as area study entire the for summarized first are Results Calculating Connectivity daily timestep. at each were randomlyselectedandremovedfromthelarvaeremaining centages ofthelarvalpopulation per- these rate, mortality daily each For 2000). al. et (Cowen values known of spectrum the reflect to 46% In the present study, we investigated the influence of a range of daily mortality rates including 3%, 18%, and YCOM Validation e s u lts

an d Disc u ssion SEC =SouthEquatorial Current,SECC=South EquatorialCounterCurrent. ENSO, neutral = na Niña, La = LN Niño, El = EN data. drifter on based conditions Figure 3.5. Box plots of median currentheadings by region, season,andENSO Median heading (°) South West East region, d Figure = Counter ata. South 100 150 200 250 300

NEl EN EN

5: season,

Equatorial

Current

= N E Box umrwne umrwinter summer winter summer El

N L

Niñ Niñ plots and a n o, SEC

LN NL LN Current, of

N E ENSO median

= N L L a conditions

Niñ Niñ a n SECC current a, N E na

= N L

South = based neutra a n headings SECC

N E Equatorial on l l

N L ENSO ENSO drifter by a n

, -

SEC SEC

page 35 Chapter 3 - Currents and Larval Connectivity page 36 Chapter 3 - Currents and Larval Connectivity net transport ofdrifterswasover Archipelago. After ~30 days,mean of theSamoan all islands includes of Savai’i,andSwains Island and tices at Rose Atoll, the westerntip of the sides of a triangle with ver- length 400 kmistheapproximate in thisregion,itisusefultonotethat ering thescaleoflarvalconnectivity reference for dimensions inconsid currents (Okubo1980). ocean As a sive natureofdispersalbyturbulent results areconsistentwiththediffu- 3.8). ger timescales(Figure These atlon- closer totheirstartingpoints many driftersback currents looped off between 50and100daysas es were40-70%shorterandleveled distanc- net displacement whereas to timeatlarge related linearly and length ofdrifters)waspositively Gross transportdistance(path terns. the effects ofENSOoncurrent pat- necessary to more fullyunderstand be would ENSO conditions varying of drifter data and modelrunswith been deployed. years Additional the timedriftershave curred during the SouthernOscillationconditionsthat oc- to limited was analysis the Unfortunately, years wouldhavegreater independence. drifters among and the analysis in included period. Ideally, many El Niño years analysis could the be in occurred year Niño El one be noted thatonly itshould ers, however ENSO didnothaveamajoreffect ondrift- alone (Table 3.2,Figure3.7). orENSO region, season, by significantly influenced not speed drifter with cm/s 30 at 20to the studyregion form throughout Niño El the year.uni- largely were speeds Current to relative years ENSO neu- tral and Niña La in variable more were minor andindirecteffect inthatheadings and contributedonlya on drifterheadings influence significant a not was ENSO rent. Counter Cur- gion oftheSouthEquatorial with most heading ESE. This marks the re- wherein drifter motion was nearly opposite between ~8ºS and 12ºS during summer, region waswestwardexcept in the region - mean drifterspeed.Significanteffects arelabeledaccordingtothelevelofsignificance. TableFull factorial 3.2. ANOVA ontheeffects ofregion,season,andENSOstatuson F-statistic: 3.209on 11 and267DF, p-value: 0.0004 Multiple R-squared: 0.11, Adjusted R-squared:0.08 Residual standard error: 6.64on267degreesoffreedom Signif. codes:p<0.001(***);0.01 (**);andp<0.05(*) median drifter heading. Significant effects are labeled according to the level of significance. TableFull factorial 3.1. ANOVA ontheeffects ofregion,season,andENSOstatuson F-statistic: 38.7on11 and266DF, p-value:<2.2e-16 Multiple R-squared:0.62, Adjusted R-squared:0.6 Residual standarderror:38.12on266degreesoffreedom Signif. codes:p<0.001(***);0.01(**);and0.05(*) einsao:NO2497298 . 0.006** 5.2 229.84 459.7 2 Residuals region:season:ENSO season:ENSO region:ENSO region:season ENSO season region Variables region einsao:NO26236020.810 0.2 306 612 2 Residuals region:season:ENSO season:ENSO region:ENSO region:season ENSO season Variables Figure 3.6.Mediancurrentheadingsbyseasonandregionbasedondrifterdata. SEC SECC

winter W

position (269°)

winter Figure based SEC (259°)

summer 6 175244.06 11,765.2 267 6 8,9 1,453 386,599 266 D D 501.8040.672 0.705 8.3e-05*** 0.164 9.7 0.4 0.1 0.366 0.914 428.83 17.48 1.8 6.29 857.7 0.8 0.01 35.0 80.02 2 6.3 36.13 0.51 2 160.0 1 36.1 2 0.5 1 1

,7 ,3 . 0.165 0.009** 1.8 0.473 2.0e-07*** 4.8 2,637 28.5 0.8 6,909 5,274 <2.2e-16*** 41,411 13,818 <2.2e-16 *** 1,091 2 289.7 41,411 2 92.4 2,182 421,055 1 421,055 134,317 2 134,317 1 1

on 6: u q enS.Fvlepvalue Fvalue MeanSq. SumSq. f u q enS.Fvlepvalue Fvalue MeanSq. SumSq. f

Median drifter

(225.5°) data. current N S headings

by

season and SECC

region

summer

(154°) E

nent of the SEC seldom extends far below ~9º S nent oftheSEC seldomextendsfar below and years, thiscompo- seasons among variable drifter datais~25cm/s. is its latitude Although (Figures 3.3and3.10). Typicalon velocity based of thestudyareaduring most seasons andyears vectors alongthenorthern edge southwestward (SEC). The SECisvisibleaswestwardorsouth- Current Equatorial South flowing westward the is Gyre Pacific South the of edge northern The (north oftheSouthEquatorialCounterCurrent) South EquatorialCurrent features inthestudyareaaredescribedbelow. current of thesefourmajor for each variability tion, andstrength,aswellyearlyseasonal feature. over thisgeologic tion posi- The heading, the Tonga Trench Eddyduetoitsconsistentposi- to as referred hereafter south ofthearchipelago, eddy occurring and 4)aregularly archipelago, Current directlyacrossthe the SouthEquatorial seasonally bifurcates the surface flow of the South Equatorial Current, 3) a westward but meandering that flow of Current Counter Equatorial South flowing eastward the 2) area, study the of edge northern the at rent Cur- Equatorial South flowing westward the 1) are: these south to north From 3.10a-b). (Figure archipelago affect the that identified were eddies or currents surface major 4 tracks, drifter and vectors current modeled the of analysis on and Delcroix1999, TomczakBased andGodfrey 2003,Craig2009)(Chapter2Figure2.3). Pacific Gyre, a series of connected ocean currents with a counter-clockwise flow that spans the Pacific basin (Alory ago lies along the northern edge of the South At thebroadestscale,Samoan Archipel- Ocean Currents Quantitative tially couldbeinfinite. essen- distances gross whereas km wide) limited bythesizeofstudyarea(~1300 was mum nettransportdistancepossible be interpretedwithcarebecausethemaxi- difference innetandgrosstransportmust large for twice aslong(Figure3.9b). The from theirstartingpointsdespitebeingat on currentsoreddiesandendedupnotfar because manydriftersactuallyloopedback tance traveled between50and100days however, therewaslittledifference indis- traveled (Figure3.9a).Fornetdistance the tailsindistributionof gross distance more extreme and the range the greater expected, the longer drifterswereat large, associated with each durationof drift. As of transport distances the spread acterize days. 30 to char- were used histograms In addition, ≥ PLD a with larvae for islands ample opportunityforconnectionsamong drifters wasover1000kmindicating vidual gross transportofsomeindi 400 kmand D escription of R egional - Counter Current. neutral ENSO, SEC = South EquatorialCurrent,SECC= South Equatorial = na Niña, La = LN Niño, El = EN data. drifter on based conditions ENSO Figure currentspeedsbyregion,season, and 3.7. Boxplotsofmedian Current, NL LN Figure and Mean Speed (cm/s)

=

10 20 30 40 50 60 30, 50,and100 days. Figure ofdrifters after10,20, 3.8. Meangrossand netdisplacement ENSO L a

7:

Niñ Niñ

SECC N E Box conditions umrwne umrwinter summer winter summer a, N L

plots na

=

South a n = SEC neutra

of N E

based current

Equatorial N L l l

ENSO ENSO a n

on speeds N E

drifter ,

SEC SEC Counter N L

= by a n SECC data. S Sh

out region, N E

Current

h EN

N L E il E quator

= season, a n El

Niño, i a l

page

37 Chapter 3 - Currents and Larval Connectivity page 38 Chapter 3 - Currents and Larval Connectivity American Samoa often lies in the middle of the SECC current field. The eastern end of this current generally cline the SEC continues a weak westward flow (Kessler and Taft 1987). Swains Island in the northern EEZ of at~200mdepth(Kessler and the mainthermocline above Taftthe thermo- and Qui2004).Below 1987,Chen (Figures 3.2,3.4, and3.10). current featureintheregion visualized current thatexists The SECCis ashallow Equatorial South flowing eastward the lies S Current (SECC)(Kesslerand Counter Taft12º et al.2007),themostclearly and Qiu,2004,Domokos 1987,Chen and S ~8º between latitudes at SEC the on Embedded South EquatorialCounter Current apparent betweentheSECandoppositeflowing SouthEquatorialCounterCurrentdescribednext. is et al.2007) 2004, Domokos and Chen half ofthestudyarea)(Qui to thesouthern eddy formation(relative not necessarilyevidentinthestudy region inrecentyears. A narrow regionbetween~6ºS and 9ºS of mild gest fromMarchtoJulyandweakestOctober toFebruary(Kesslerand Taftthis was 1987), although or intotheEEZ of American Samoaor(Kesslerand Taft asstron- 1987). Flowhasbeencharacterized Figure 3.9a.Grossdisplacementofindividualdriftersasafrequencyhistogram after10,20,30,50and100daysatlarge. during various ENSOconditions. These conditions. Niña study between ENSOand SECC andtheneedforadditional the irregularcorrelations highlight observations La of period a 2009, throughout absent virtually also was SECC the note, of Also and Taft(Kessler 1983 of conditions Niño El strong 1987). the bounded that years ENSO neutral 1984, and 1982 throughout absent was SECC Interestingly,the year. Niño El an 2005, in observed was as yearlong these wintermonths(Figures 3.6and3.7). cm/s during of thiscurrent canhowever,The signature bepresent Chen 2004), as confirmed by meandering or even westward drifter tracks and lower drifter speeds of 19 to 25 3.5-3.7). and Qui2004, (Chen or absentinMaythroughSeptember The currentisoftendissipated is east-southeast(Figures based ondriftersrangefrom22to30cm/sand currentheading summer velocities October and April withpeakspeedandwidthobservedduringJanuaryFebruaryinthisregion. Typical across theSamoan (Chen andQui2004). Archipelago in mostyearsbetween developed The SECCiswell curls south between ~160º and170º W and ultimately joinsthe southern componentof the SEC headed west depicts nettransportdistancesgreaterthanthemaximum possibility asdeterminedbythesizeofstudyarea(~1,300kmwide). Figure 3.9b. Net displacement ofdrifters individual as a frequency histogramafter 10, 20 ,30, 50 and100daysat large. Grey shading page 39 Chapter 3 - Currents and Larval Connectivity page 40 Chapter 3 - Currents and Larval Connectivity (2004-2009) and NOAA’s Global DrifterProgram(n=216). patterns only. general and denote curled currentvectors andmeandersarehighly variable Patterns arebasedondata fromHYCOM September.for Maythrough region surrounding EEZs and Figure 3.10b.Surfacecurrentpatternsofthe Samoan of The position 2009) andNOAA’s GlobalDrifterProgram(n=216). and denotegeneralpatternsonly.variable are highly current vectorsandmeanders PatternsarebasedondatafromHYCOM(2004- Figure 3.10a. SurfacecurrentpatternsoftheSamoanEEZsregionforOctoberthrough and surrounding April. The positionofcurled 20°S 15°S 10°S 20°S 15°S 10°S South Equatorial South Counter Equatorial Current Wallis Wallis 175°W 175°W Tonga Tonga Tokelau Tokelau Swains Swains Swains Swains 170°W 170°W Niue Niue Rose Rose Atoll Rose Rose Atoll 165°W 165°W CookIslands CookIslands F F 160°W 160°W denotes larval sources from American Samoa.Greenshading denotessourcesfromSamoa. Figure 3.11.group. Redshading of virtuallarvaeinthestudyarea thatwerestartedfromeach island,seamount,orisland Proportion eddies anddynamicsrecentlyinvestigatedbyDomokosetal.(2007). present throughout 2009. was This featureispersistentandnottobeconfusedwiththerelativelyshort-lived(~weekly) eddy the 2008, September in Beginning conditions. Niña La moderate or mild to correspond 3.3). in 2006,2008,and2009,allofwhich December through The eddywasmostcommoninSeptember W,172º over the approximately Islands andpositioned south oftheSamoan alocation Tonga Trench (Figure The lastfeatureofnoteisaclockwiseeddy(negativevorticity)centeredat16ºSand regularly occurring Tonga Trench Eddy (Domokos etal.2007). Much irregular eddy activity is apparent between the opposite flowing SECC and this component of the SEC of (mean heading225ºinsummerto 269º inwinter)(Figures3.4- 3.6). Typical velocitiesare~25cm/s. drifters of tracks westward overall the by confirmed is and 3.10) and 3.2 (Figures seasons and years all for dies (Domokos et al. 2007). This overall westward but meandering flow pattern is apparent in current vectors of the SEC described above,the SEC in this region is characterized by many irregularmeandersanded- of theSamoan andthesouthernhalfofstudyregion.Incontrasttonortherncomponent Archipelago The SEC continues its westward flow south of the SECC between ~13º S and 19º S, including all the islands South EquatorialCurrent(southoftheCounterCurrent) page 41 Chapter 3 - Currents and Larval Connectivity page 42 Chapter 3 - Currents and Larval Connectivity feedback loop feedback loop to the SEC would carrylarvaefrom sites such as SwainsIslandback along theSamoan its and SECC flowing eastward the that expectations Despite west. the to islands and themselves both to larvae to theeastproviding islands by theSEC with controlled was of connectivity pattern the spatial Overall, source foreventheSamoan Archipeago, thenextislands downstream. larval significant a be to larvae few too produced and away far too simply were islands These SEC. the in upstream position and showfew withothersitesconsideredheredespite theirgenerally larval connections warrow Atoll, Palmerston Atoll, andPukapuka even fromeach other,isolated, are largely Atoll and Nassau) Samoan via the returnloopof Archipelago the SECC. Islands andseamountsin the CookIslandsgroup(Su- to the minor larvalcontributions in thestudyareaandaresourcesofonly relatively from theotherislands its associated SwainsIslandand seamounts andnotinveryhighproportions. Tokelau arerelativelyisolated the islandsofSamoa, butoftennotasfar destinations downstreamtothewest,including as Wallis Islandand nected. The patternoftransportissuchthatmostthelarvaeeithersettle atthesourceoraretransportedto the SECtoward American Samoa. and seamounts of The islands con- American Samoaarealsointernally (Tonga),lis, Niuafo’ou and Tafahi(Tonga). against eastward of itslarvae proportion exports asmaller Samoa to and alsohavealargeexportoflarvae theislands andseamountstothewestsuchasWalinterconnected - highly are Samoa in Savai’i and Upolu elapsed. PLD their until larvae many entrained which groups island of the have beenstrongerwereitnotforthefrequentdevelopment Tonga Trench Eddybetweenthesetwo neighbor, withitsnearestdownstream Connections islands. downstream from bothupstreamand Tongamay seamounts, isfrom largely isolated theotherislandsinstudyregion. This isdueto Niue’s long distance as sourcesintheanalysis. not included The islandnationsouthof American Samoa,Niueanditsassociated were in thesegroups that someoftheislands ofFiji.Infact,thisisthereason in thedirection study region ally transportedwestwardout of the gradu- from thembeing the larvae of the study arearesultsin most of region or southwestern the western the studyregion. in in Their position Samoan or elsewhere Archipelago ed butcontributefewlarvaeto the with themarestronglyinterconnect associated seamounts and islands Wallis, Tonga, andthemanysmall connectivity matricesitisclearthat attheoriginof 3.12). Beginning (Figure connectivity strong internal with groups island port andseveral broad patternsof overall larvaltrans- The connectivitymatricesreveal Larval Connectivity: Overall Patterns vae trackedinthestudy. the sourceof over halfthevirtuallar- Samoa and Samoa were American Table 3.3). Altogether theislandsof out ofthestudyarea(Figure3.11, are quicklytransportedwestward nating fromthismorediffuse group although many of the larvae origi the Wallisand (~15%), group Island (~15%), Savai’i of thetotallarvae), (~25% Upolu be to likely are region major sources of larvae inthestudy Based onpotentialreefarea,the Larval Sources - - denotes islandsandseamountsof American Samoa. larval poolcontributedbyeachsource.GreenshadingdenotesislandsofSamoa.Red shelf), numberofvirtuallarvaeusedinmodeling,andthepercentagesimulated tions ofregionallarvalconnectivity, theircorrespondingpotentialreefarea(0-150m Table 3.3.Islands,seamounts,orislandgroupsusedassourcelocationsinsimula- Site Total Palmerston Atoll Suwarrow Atoll Pukapuka andNassau Tokelau Swains Island Rose Atoll Manu’a Islands Northeast Bank(MuliGuyot) East Bank(Tulaga Seamount) South Bank(PapatuaGuyot) Tutuila Upolu North Upolu South Savai’i North Savai’i South Niue Tafahi andSeamounts Pasco and Toafilemu Seamounts Niuafo’ou andSeamounts Wallis andSeamounts R Potential eef Area ,7 1,1 100.00 817,010 6,077 (km 0 6763.3 3.0 5.6 26,796 24,507 45,644 3.1 203 187 350 25,182 9.5 15.6 186 9.4 77,873 9.9 127,661 4.9 76,831 4.9 576 80,919 6.7 949 39,793 4.5 571 40,304 600 54,704 16.2 300 37,067 285 400 132,722 279 993 01,4 1.5 12,440 90 16 12 10 33 34 3 2 ) No. Larvae Spawned ,3 0.3 0.2 2,133 0.2 1,564 0.6 1,335 4,481 0.6 4,606 448 Spawned Percent Larvae 0.1 Figure 3.12. Cumulative connectivity, 2004-2008. Color scale indicates fraction of simulated larvae released at source settling at destination. Shading of labels indicates core island groups: red, American Samoa; green, Samoa. page 43 Chapter 3 - Currents and Larval Connectivity page 44 Chapter 3 - Currents and Larval Connectivity information on larvalmortality, particularlyforspecies withlongPLDs. ner). PLDs. before theendof theseverylong died They all simply of better the importance This highlights (Figure 3.12;threematricesinlowerright cor- no larvaesettledsuccessfully atanyislands rates considered, connectivity. hadanymeasureable close together to highmortality FortheverylongestPLDs and medium were that Wallis)or Upolu, Savai’i, (e.g. sources larval large were that islands those only mortality of levels PLDs. at longer (many moreblankcells), especially connections as thespatialpatternofisland well At high (Figure 3.12).In contrast, higher mortalityrates affected both thestrengthof the connections(cell color)as affectdid not) the matrixdid in but patternofemptycells changed color (cell thestrengthofconnection little, butmortality andPLD changed in predictedlarvalexchange at PLDsupto30days,theislandsinvolved on mortalityrates.Forlowtomoderatedaily mortalityrates dependent larvae ishighly The fateoflong-lived disturbance andresponsestoclimatechangeof thisregionalecosystem. to resilience and predicting be importantinunderstanding PLDs could with longer transport oforganisms larvae arrive in low density is influenced by a variety of life history features (Kinlan et al. 2005). Widespread rapid (re-)colonizationofreefs, of actuallyoccurringwhen unoccupied althoughthelikelihoodcolonization eration timeof many speciesinSamoan reefecosystems. transport couldalsopromote This widespread that our study reflects cumulative connectivity over only a five year period, which is short relative to the gen- by genetic driftiseasilypossiblethroughoutthestudyarea. divergence true considering This isespecially to preventspecies potential fortransportatlongPLDssuggeststhatthelowamountofconnectivityneeded that themortalityratewaslowenough. provided study areaalthoughinverylowabundance This widespread from American Samoa. Third, larvae withPLDsof 50 or 100 dayscouldbetransportednearlyanyplaceinthe of Wallis,in seeding noticeable (Tonga), Niuafo’ou Tafahi (Tonga), andthenearbyseamountswithlarvae connectivity withislandsfartherdownstreamincreasednoticeablyafter PLDs of10days. This wasespecially farther fromsources.Second, transported been they had to settleuntil not competent were larvae since all seeding (fractionof larvae producedatasourcelocationthat settled atthesamelocation)wasreducedover- Longer PLDshadthreemaineffects connectivity(Figure3.12).First,ofself on inter-islandtheproportion Influence ofPLDandDailyMortalityRate for somepopulationmodelingpurposes. we donottheconnectivityvaluesforsizeofdestinationarea,althoughthismaybe desirable standardize island anditssettlementzone).Sincethis surrounding isaninherentfeatureof the geographyof the region, size, and ocean current patterns, but also of the size of the destination (specifically, the size of the destination locations, population of source not only will beafunction to adestination traveling of larvae The proportion tively lessprobable. but insteadthoughtofasrela- connections as impossible not beviewed should cells inour simulations blank spawning event involving manymorelarvae,somemayhaveactuallymadethe connection. For this reason, or inarealworld connected asourceanddestination,buthadweusedmorevirtuallarvaeinthesimulation systems isordersofmagnitudehigher. Blankcellsinourmatricesdenotecaseswhichzerovirtuallarvae output ofthesemarine virtual larvae,thereallarval we tracked>800,000 Also importantisthat,whereas Samoa arethemostrobust. in thecontext of the study extent. Findings for islands in thecoreof the studyarea, American Samoaand only of thestudyareamustbeinterpreted near theedge for islands matrix elements Fiji). Forthesereasons here (e.g. that werenotcharacterized just outsideofourstudyregion islands roles withadjacent destination ing of daily larvalmortality. Islands at the edge of our study extent may alsoplayimportantlarvalsourceor for larvae withlongerPLDs. The importance of these lost trajectories is probably minordueto the compound settlement back intothestudyareaforpossible larvae looped may haveeventually dies orcurrentreversals model werelosttofurthertransport.Intherealworld,ed- virtual larvaethathittheedgeofhydrodynamic An important caveat to interpretation of matrix elements for islands closeto the edges of the study area isthat current loopstocarrythembacksettlementsites. SECC current field and there are simply too few larvae that can survive the long transport time necessary for such connectivitypatternswerenotseeninthesimulations.Swainsissimplytoofar Archipelago, northinthe - the scaleofhydrodynamicmodel. and Islands (Ofu,Olosega, Manu’a Ta'u)to relative proximity close size and to theirsmall due arecombined characterized separatelydueto their largesizeandslightlydifferent patternsof larval connectivity. The each are Upolu and Savai’i of shores south intheregion. and destination The northand to characterizeitsroleasalarvalsource setofanalyses site isthefocusofadetailed pelago andendingwithSwainsIsland,each the archi- from west toeastalong Moving ized separatelyinthefollowingsections. in theSamoan arecharacter- Archipelago seamounts shallow and Each oftheislands within theSamoan Archipelago Larval Connectivity:Islands/Seamounts direction. Swainslarvaeintheopposite and entrained the region transport throughout westward contrast, in 2008theSECpersistedits intheSECC(Figure3.13).In ried eastward years, larvaefromSwainswerequicklycar- model most In field. current this of middle in the lies except forSwains,which region port of larvae for most islands inthestudy op. This hadonlyasmalleffect on trans- to devel a yearinwhichtheSECCfailed transport. The oneexceptionwasin2008, was borneoutinthesimulationsof larval current dataamongyears,apatternthat There waslittledifference in the drifter or Influence ofInterannual Variability - All PLDsshownassamecolorforeachyear. Figure 3.13. Transportyear.by model Island from Swains larvae of virtual page 45 Chapter 3 - Currents and Larval Connectivity page 46 Chapter 3 - Currents and Larval Connectivity S daily mortalityrespectively. 18% and 3% denote plots lower and Upper PLD. by years model all for Savai’i southern from larvae virtual of Position Figure 3.14. avai ’ i ( so u t h coast ) at thissitethat returnhere. produced larvae Percent ofsimulated at othersites.Bottompanel: produced settling atthis sitethatwere larvae Percent ofsimulated as afunctionofPLD andmortalityrate. retention atSavai’i-South supply and local larval Figure 3.15.Externallarval Top panel: rest oftheSamoan Archipelago after30to50days. ward and then entrained into the eastward flowing SECC which carries them between Swains Island and the group (Niuafo’ou, Tafahi, etc.) after only 10days(Figure3.14). A smaller numberof larvae arepassednorth- Wallisthe southwestviaSECandhavereached and seamountsofthe and thenorthernislands Tonga of thelarvaeforregion(Figure3.11, Table 3.3).MostlarvaefromSavai’i’s southcoastaretransportedto Southern Savai’ihasamoderateareaofpotentialreefcomparedtootherislandsandwasthesource5% Destinations page 47 Chapter 3 - Currents and Larval Connectivity page 48 Chapter 3 - Currents and Larval Connectivity larval mortality rates. Shadingoflabelsindicates coreislandgroups:red, American Samoa;green, Samoa.ND=nodata. Destinations (and sources) Figure of 3.16. simulated larvae originating from (arriving at) Savai’i-South for low, medium, and high slow andreliantonthemuchsmallerlarvalsourcesfrom Tutuila andtheotherislandsof American Samoa. and PLD.Werecould berelatively sources tobedisturbed,recoveryatSouthernSavai’i thesemajorlarval 3.16). Notably,rate of mortality regardless from Upolu supply of itslarval half over receives Savai’i southern come from southern Savai’i, large fractions also arrive from the northern and southern coasts of Upolu (Figure on PLDanddailymortalityrate(Figure3.15). depending Although manylarvaethatreachsouthernSavai’i larvae of itsarriving ~60-80% consistent for arelatively sources larval on outside is reliant Savai’i Southern Sources the pointthatmostlarvaeproducedatSavai’idiewithoutreachingsuitablesettlementhabitat. else either(Figure3.16). successfully settleanyplace (Figure 3.15),butverysmallproportions This highlights rates resultinonlyasmallproportionof the larvae producedat southern Savai’isuccessfullyreturningthere to thewestsuchasWallisof northern and seamounts and theislands Tongamortality 3.16). Higher (Figure mortality. end upatdestinations fraction ofthesettlinglarvae large an increasingly As PLDislengthened, higher and PLDs for longer retained are production of local fractions smaller 3.15). Much (Figure day PLD 10 and scenario mortality for thelow there retained are Savai’i from southern spawned of thelarvae 25% Nearly page 49 Chapter 3 - Currents and Larval Connectivity page 50 Chapter 3 - Currents and Larval Connectivity daily mortalityrespectively. 18% and 3% denote plots lower and Upper PLD. by years model all for Savai’i northern from larvae virtual of Position Figure 3.17. S avai ’ i ( no r t h coast ) this sitethatreturn here. at produced larvae Percent ofsimulated at other sites.Bottompanel: settling atthissite thatwereproduced larvae cent ofsimulated Figure 3.18. External larvalsupplyandlocal larvalretentionat Savai’i-North asa function of PLD andmortality rate. Top panel:Per- 20 to50daysdependingontheyear. from the south shore. Also, many morelarvaeareentrainedintothe SECC andreachSwainsafter PLDs of Wallis andfewerarecarriedtowardthesouthernpart of the Tonga Chaincomparedto the larvaeoriginating toward westward transported are 3.17). Morelarvae (Figure is shiftednorthward except thedistribution ously 3.11, Table 3.3). Transport of larvae from Savai’i’s north coastissimilarto the southshoredescribedprevi- Northern Savai’ihasalargepotentialreefareaandwasamongthelargerlarvalsourcesinstudy(Figure Destinations page 51 Chapter 3 - Currents and Larval Connectivity page 52 Chapter 3 - Currents and Larval Connectivity larval mortality rates. Shadingoflabelsindicates coreislandgroups:red, American Samoa;green, Samoa.ND=nodata. Destinations (andsources)ofsimulated larvaeoriginatingfrom(arriving at)Savai’i-Northforlow,Figure 3.19. medium,andhigh islands of American Samoa. sources from larval on themuchsmaller be reliant recovery ofnorthernSavai’iwould Tutuilaand theother for allPLDs(Figure3.19).Werethe southsidesoftheseislands degree sources disturbed, themajorlarval lesser a to and Upolu and Savai’i of sides north the from primarily come Savai’i northern reach that Larvae daily mortalityrate(Figure3.18). PLDs. at longer fraction oflarvaecomefromelsewhere An increasing on PLDand larvae depending of itsarriving is reliantonoutsidelarvalsourcesfor40-70% Northern Savai’i Sources the westascomparedtoSouthernSavai’i(Figure3.19). PLDs andhighermortalityrates. Much smallerfractionsof in Samoaandat larvae settleelsewheresitesto there forlonger are returned production fractions oflocal smaller 3.18). Progressively (Figure PLD scenarios offOver 40%ofthelarvaespawned endupsettlingthereforthelowmortalityand10day northernSavai’i page 53 Chapter 3 - Currents and Larval Connectivity page 54 Chapter 3 - Currents and Larval Connectivity daily mortalityrespectively. 18% and 3% denote plots lower and Upper PLD. by years model all for Upolu southern from larvae virtual of Position Figure 3.20. Upol u ( so u t h coast ) this sitethatreturn here. at produced larvae Percent ofsimulated at other sites.Bottompanel: settling atthissite thatwereproduced larvae cent ofsimulated Figure 3.21. External larvalsupply and local larval retentionat Upolu-South as a function of PLD andmortality rate. Top panel:Per- PLDs andhigher there forlonger are returned production fractions oflocal (Figure 3.21).Muchsmaller nario Over 20% of larvae spawned at southern Upolu are retained there for the low mortality and 10 day PLD sce- Swains IslandtothenorthandrestofSamoan Archipelago tothesouthafter20-50days. between them eastward send can ultimately in theSECCwhich are entrained and Savai’i or around Savai’i ported westward or southwestward in the SEC (Figure 3.20). Some larvae slip northward between Upolu and 3.11,(Figure region the for Upolu’slarvae of source large a is coast south Tabletrans- are larvae Most 3.3). Destinations page 55 Chapter 3 - Currents and Larval Connectivity page 56 Chapter 3 - Currents and Larval Connectivity larval mortality rates. Shadingoflabelsindicates coreislandgroups:red, American Samoa;green, Samoa.ND=nodata. high and medium, low, for Upolu-South at) (arriving from originating larvae simulated of sources) (and Destinations Figure 3.22. these larvalsourcesforsouthernUpolu(Figure3.22). Tutuilaof withPLDforscenarioslowor moderatemortalityanddemonstratestheimportance increases larvae with longer PLDs arrive from outside sources. The fraction of larvae arriving from northern Upolu and daily mortalityrate(Figure3.21). At short PLDstheareaisseededprimarilyfrom local productionwhereas and PLD on depending larvae arriving its of 15-70% for sources larval outside on reliant is Upolu Southern Sources destinations forPLDsof20-50daysevenunderscenarioswithmoderatemortality. cially for short PLDs (Figure 3.22). Wallis and its neighboring seamounts as well as Niuafo’ou are significant mortality. A large proportion of the larvae from Upolu’s south coast settle back on the Islands of Samoa espe- page 57 Chapter 3 - Currents and Larval Connectivity page 58 Chapter 3 - Currents and Larval Connectivity daily mortalityrespectively. 18% and 3% denote plots lower and Upper PLD. by years model all for Upolu northern from larvae virtual of Position Figure 3.23. Upol u ( no r t h coast ) this sitethatreturn here. at produced larvae Percent ofsimulated at other sites.Bottompanel: settling atthissite thatwereproduced larvae cent ofsimulated rate. mortality Topand PLD of function a as Upolu-North at retention larval local and Per- supply panel: larval External Figure 3.24. Nassau intheCookIslands. to thesouthafter20-50days.Somein50dayrangehavereachedasfarPukapukaand Archipelago in theSECCareultimatelysenteastwardbetweenSwainsIslandto the northand therestof the Samoan southwestward intheSECandhavereachedWallis andnorthern Tonga after only 10days.Larvaeentrained or westward are trajected 3.23). Mostlarvae (Figure into theSECC entrained with morelarvae northward The patternof dispersal issimilarto the southerncoastdescribedpreviouslybutdistributionisshifted poten- more with Archipelago Samoan the of seamounts and the islands than all reef area tial in 3.11,(Figure combined Samoa American Tablelarvae 3.3). of source largest the is Upolu of coast northern The Destinations page 59 Chapter 3 - Currents and Larval Connectivity page 60 Chapter 3 - Currents and Larval Connectivity larval mortality rates. Shadingoflabelsindicates coreislandgroups:red, American Samoa;green, Samoa.ND=nodata. high and medium, low, for Upolu-North at) (arriving from originating larvae simulated of sources) (and Destinations Figure 3.25. Samoa forrecovery. be reliantonthesmallersourcesof tion tobedisturbed,itwould Tutuilaof andtheotherislands American larval supply is relatively minor compared to self-seeding (Figure 3.25). Were northern Upolu’s larval produc moderate mortality. The next highest source of larvae for northern Upolu is Tutuila although the proportion of with lowor locally forPLDsupto50daysandscenarios of thesuccessfullysettlinglarvaehereareproduced and dailymortalityrate (Figure 3.24). The site is among the least reliantonoutsidelarvalsourcessincemost PLD on depending larvae arriving its of 10-35% only for sources larval outside on reliant is Upolu Northern Sources sce- mortality all narios (Figure3.25). for Savai’i at settle Upolu northern from larvae of proportion large Ascenarios. mortality (Figure 3.24). Smaller fractions of local production are returned to northern Upolu for longer PLDs and higher scenarios mortality low and PLD short the for there return coast north Upolu’s from larvae the of 40% Over - page 61 Chapter 3 - Currents and Larval Connectivity page 62 Chapter 3 - Currents and Larval Connectivity tality respectively. Figure 3.26. Position of virtual larvae from Tutuila for all model years by PLD. Upper and lower plots denote 3% and 18% daily mor- Tu t u ila site thatreturn here. at this produced larvae Percent of simulated at othersites. Bottompanel: settling atthissitethat wereproduced larvae of simulated Figure 3.27. External larvalsupplyandlocal larval retentionat Tutuila asafunctionof PLD andmortalityrate. Top panel:Percent and passsouthofSwainsIslandwithlittlesettlementoccurringthere. Trench Eddy. Larvae trajectednorthof Tutuila that are entrainedintothe SECC arequicklysweptto the east its seamounts farther neighboring west. Many larvaetrajectedsouthof Tutuila areentrainedinthe Tonga reach Tafahiof the in thenorthernend Tongainto Wallisare well days larvae By PLDsof20-50 chain. and shores ofSamoa(Figure3.26). to and begun western Savai’i have justpassed At PLDsof10days,larvae Transportfrom of larvae Tutuilasouth the northand along splits intotwogroups the SECand in is westward comparatively small relative to Savai’i and Upolu as a source of larvae to the region (Figure 3.11, Table 3.3). Tutuilaand seamountsin reefarearelativetothe otherislands hasalargepotential American Samoabutis Destinations page 63 Chapter 3 - Currents and Larval Connectivity page 64 Chapter 3 - Currents and Larval Connectivity mortality rates. Shadingoflabelsindicatescore islandgroups:red, American Samoa;green, Samoa.ND= no data. Figure 3.28. Destinations (and sources)of simulated larvae originatingfrom (arriving at) Tutuila for low, medium, andhighlarval be importantto Tutuila’s recoveryiflocallarvalproductionweredisrupted. 3.28). The Manu’a Islands, Upolu, and even Savai’i are the most notable sources of outside larvae and would is low.mortality when that reach Larvae Tutuilafrom primarily come Tutuila(Figure at shortPLDs especially PLDs, especially at longer more important proportionally become 3.27). Outsidesources tality rate(Figure Tutuilaon PLDanddailymor- larvae depending ofitsarriving larvalsourcesfor10-65% onoutside isreliant Sources southern extent Upolu, northernSavai’i,andWallis andthenorthern Tonganlesser a IslandsforlongerPLDs(Figure3.28). to and Upolu, northern at primarily settle exported are that Larvae 3.27). (Figure scenarios mortality higher and PLDs for longer there returned are production of local fractions smaller Much Nearly 40%ofthelarvaespawnedat Tutuila settlebackthereforthe10dayPLDandlowmortalityscenario. page 65 Chapter 3 - Currents and Larval Connectivity page 66 Chapter 3 - Currents and Larval Connectivity mortality respectively. Figure 3.29. Position of virtual larvae from South Bank for all model years by PLD. Upper and lower plots denote 3% and 18% daily S o u t h B an k site thatreturn here. at this produced larvae Percent ofsimulated at othersites.Bottompanel: settling atthissitethatwereproduced larvae of simulated mortality rate. of PLD and at SouthBankasafunction retention larval local supply and larval Figure 3.30.External TopPercent panel: (Tonga), orsouthwardintothe Tonga Trench Eddy. the Samoan (Figure 3.29). Archipelago Transport iseitherwestwardintheSECbetweenSavai’iand Tafahi of islands north between are transportedsouthandwestfromthissitewithveryfewslipping Most larvae Tutuila andprovidesaverysmallcontributionto the totallarvalpoolofregion(Figure3.11, Table 3.3). small guyotsouthof South Bank(PapatuaGuyotinSeamountCatalog,Koppersetal.2010)isarelatively Destinations page 67 Chapter 3 - Currents and Larval Connectivity page 68 Chapter 3 - Currents and Larval Connectivity larval mortality rates. Shadingoflabelsindicates coreislandgroups:red, American Samoa; green,Samoa.ND= no data. at) SouthBankforlow,from (arriving originating larvae (and sources)ofsimulated Figure 3.31.Destinations medium,andhigh turbed, SouthBankwouldrelyprimarilyonUpoluasalarvalsource. sources of larvae for South Bankare Tutuila andManu’a(Figure3.31).Were theseprimarysourcesdis- proportion, 80-95%,of its arriving larvaeregardlessof PLD ordailymortalityrate(Figure3.30). The major large very a for sources larval outside on reliant is Bank South far, thus discussed sites other most Unlike Sources bathymetry. reef areainferredfrom Bank isevenlessofalarvalsourcethanestimatedherebasedpurelyonthepotential runs. ItalsosuggeststhatSouth by ourmodel predicted supply low larval is consistentwiththechronically CRED andD.Fenner, American SamoaDMWRpers.comm.),whichcouldindicaterecruitmentlimitationand of South Bank indicate that the seamount is relatively uncolonized by corals and reef fish (R. Brainard, NOAA noticeable proportion of the larvae originating from South Bank at longer PLDs. Of note, recent field surveys larvae inthe10-50PLDranges(Figure3.31). Tafahi (Tonga), Wallis, andothersitesnearthemreceivea of proportion significant a receive Upolu Tutuilaand 3.30). (Figure scenario mortality or PLD any for locally In contrast to the othersitesdiscussedsofar, a verylowproportionof larvae from South Bankareretained page 69 Chapter 3 - Currents and Larval Connectivity page 70 Chapter 3 - Currents and Larval Connectivity East mortality respectively. daily 18% and 3% denote plots lower and Upper PLD. by years model all for Bank East from larvae virtual of Position Figure 3.32. B an k site thatreturn here. at this produced larvae Percent of simulated at othersites. Bottompanel: settling atthissitethat wereproduced larvae of simulated at EastBankasafunctionofPLDand mortalityrate. larval retention supply and local larval Figure 3.33.External TopPercent panel: starting larvaespawnedinthesimulation. ward towardNiuebutfewarrivedueto the longtransportdistance,larvalmortality, and thelownumberof the northandsouthshoresofSamoan along (Figure 3.32).Othersaretransported south- Archipelago pool inthisstudy(Figure3.11, Table 3.3).ManylarvaefromEastBankaretrajectedwestwardintheSEC eastfrom ridge extending Tutuila.larval Duetoitssmallreefareaitisaverycontributortheregional East Bank (Tulaga seamount inSeamountCatalog,Kopperset al. 2010) is the shallow crest of a submerged Destinations page 71 Chapter 3 - Currents and Larval Connectivity page 72 Chapter 3 - Currents and Larval Connectivity larval mortality rates. Shadingoflabelsindicates coreislandgroups:red, American Samoa; green,Samoa.ND= no data. at) EastBankforlow,from (arriving originating larvae (and sources)ofsimulated Figure 3.34.Destinations and high medium, north, forthe100dayPLDwithlowmortalityrate. a (muchsmaller)larvalsource. Aof larvaearefrom proportion smallbutmeasureable Tokelau, welltothe starting from Manu’a. Were these larval sources to be disturbed, East Bank would rely primarily on Upolu as from Tutuila at 20 to 30 dayPLDsespeciallyat higher mortalityrates given the relatively lownumberof larvae 3.34). (Figure days forPLDsof10-30 East BankarefromManu’a Asettlers come of successful fraction large of PLDordailymortalityrate(Figure3.33). of itsarrivinglarvaeregardless The majorityoflarvaesettlingat 95-100%, proportion, for averylarge sources larval on outside to SouthBank,EastBankisreliant Similar Sources connections westofSavai’idespiteprevailingcurrents. mortality,PLDs, high PLDs (Figure3.34).Notethatlonger with resultinfewstrong to begin andfewlarvae at South Bank at the 10 day PLD, Tutuila and Upolu at 20 to 30 day PLDs and islands farther west for longer larvae(Figure3.33). East Bankhasvirtuallynoretentionoflocallyproduced Aof highproportionlarvaesettle page 73 Chapter 3 - Currents and Larval Connectivity page 74 Chapter 3 - Currents and Larval Connectivity daily mortalityrespectively. 18% and 3% denote plots lower and Upper PLD. by years model all for Bank Northeast from larvae virtual of Position Figure 3.35. N o r t he ast B an k at thissitethat returnhere. produced larvae Percent ofsimulated at othersites.Bottompanel: produced settling atthis sitethatwere larvae Percent ofsimulated retention atNortheastBankasafunctionof PLDandmortalityrate. larval supply and local larval Figure 3.36.External Top panel: reaching Niue. of the in theregion trajected southandexpire Islands. Manyarealso the Cook Tonga Trenchto Eddy prior of SwainsIslandwheretheyarelargelydispersedanddieintheopenoceanbetween American Samoaand the Samoan Archipelago (Figure 3.35). Many are quickly entrained in the eastward flowing SECC well south gion (Figure3.11, Tablethe northsideof 3.3).MostlarvaefromNortheastBankaretrajectedwestwardalong and Manu’a.DuetoitssmallsizeNortheastBankisaveryminorcontributorthetotallarvalpoolofre- Northeast Bank(MuliGuyot in SeamountCatalog,Kopperset al. 2010)isasmallseamountbetween Tutuila Destinations page 75 Chapter 3 - Currents and Larval Connectivity page 76 Chapter 3 - Currents and Larval Connectivity larval mortality rates. Shadingoflabelsindicates coreislandgroups:red, American Samoa;green, Samoa.ND=nodata. Destinations (and sources) of simulated larvae originating from Figure (arriving 3.37. at) Northeast Bank for low, medium, and high larvae arefrom Tokelau inthe100dayPLDwithlowmortalityrate. at NortheastBankafter18-30days. in theSECCandarrived trained Aof proportion smallbutmeasureable en- quickly were 2006 from Upolu. larvae northern of Ais group range large PLD day 30-50 the in larvae of 10 day PLD arrive at Northeast Bank from the Manu’a Islands (Figure 3.37). Interestingly, a significant source 100% of its arrivinglarvaeregardlessof PLD ordailymortalityrate(Figure3.36). The majorityof larvae witha Like theotherseamountsof American Samoa,NortheastBankisreliantonoutsidelarvalsourcesfor90- Sources detected. starting from Northeast Bank are largelydeadafter the 10dayPLDandnoconnectionsamongislandswere to Wallisthe way farther westall islands seamounts. its associated and rates, thefewlarvae mortality At high the along spread of larvae days resultinamoreevendispersal PLDs of30-50 (Figure 3.37).Longer Savai’i and Upolu of coasts north the and Tutuila, Bank, South at up end Bank Northeast from larvae most days, 3.36). ForshortPLDsof10-30 (Figure larvae produced of locally no retention Bank hasvirtually Northeast page 77 Chapter 3 - Currents and Larval Connectivity page 78 Chapter 3 - Currents and Larval Connectivity Position of virtual larvae from Manu’a for all model years by PLD. Upper and lower plots denote 3% and 18% daily 18% and 3% denote plots lower and mortality respectively.Upper PLD. by years model all for Manu’a from larvae virtual of Position Figure 3.38. M an u’ a I slan d s site thatreturn here. at this produced larvae Percent of simulated at othersites. Bottompanel: settling atthissitethat wereproduced larvae of simulated Figure larvalretentionatManu’aasafunctionofPLDandmortality rate. 3.39. Externallarvalsupplyandlocal Top panel:Percent (Figure 3.39). Much smallerfractions of local productionareretainedlocallyfor longer PLDsandhighermor- Over 20% of the larvae spawnedat Manu’a areretainedtherefor the 10dayPLDandlowmortalityscenario Swains wherethey mostly expire inthe open oceanbetweenthe Samoan and the Archipelago CookIslands. Eddy (Figure3.38). Many inthenortherntrajectoryareentrained SEC andtransportedwellsouthof side oftheSamoan into theregionof and anotherthatiscastsouthwestward Archipelago Tonga Trench moan (Figure 3.11,Archipelago Table 3.3).LarvaefromManu’asplitintotwogroups,onealongthenorthern Islands of The Manu’a Ta’u,sized sourceoflarvaeintheSa- Ofu,thelastmoderately and Olosegarepresent Destinations page 79 Chapter 3 - Currents and Larval Connectivity page 80 Chapter 3 - Currents and Larval Connectivity mortality rates. Shadingoflabelsindicatescore islandgroups:red, American Samoa;green, Samoa.ND= no data. for low,at) Manu’a from(arriving Figure larvae originating 3.40. Destinations(and sources)ofsimulated medium,andhighlarval from Tokelau tothenorthandPukapukaNassau,Suwarroweast. are in thelowtomoderatemortalityratescenarios at Manu’a to the larvaearriving contributions measureable back southalongthe Samoan Manu’a inthe including 50-100dayrange(Figure3.40). Archipelago Smallbut include sources PLDs, Tutuila fed then and SECC flowing eastward the in entrained larvae with Samoa and day PLDrange.Forlonger in the10-30 occurs forlarvae of selfseeding proportion a high whereas sources pending onPLDanddailymortalityrate (Figure 3.39). Nearly alllarvaewitha 100 dayPLDarefrom outside larvae de- Islands arereliantonoutsidelarvalsourcesforawiderange,0-90%,oftheirarriving The Manu’a Sources islands andseamountsinthe50-100dayrangelowtomoderatemortalityscenarios. Wallisin similarproportions(Figure3.40).Larvaearethenspreadfartherwestwardreaching andnearby tality scenarios. Larvaesettle along theon archipelago seamounts, Tutuila, andthe islands of Samoa page 81 Chapter 3 - Currents and Larval Connectivity page 82 Chapter 3 - Currents and Larval Connectivity mortality respectively. daily 18% and 3% denote plots lower and Upper PLD. by years model all Rose for from Atoll larvae virtual of Position Figure 3.41. OLL Ros e A t site thatreturn here. at this produced larvae Percent of simulated at othersites. Bottompanel: settling atthissitethat wereproduced larvae of simulated Figure 3.42. External larvalsupplyandlocal larvalretentionat Rose Atoll asafunctionof PLD andmortalityrate. Top panel:Percent Rose days PLDs of30-100 3.43). Longer (Figure Islands Manu’a or atthenearby locally Atoll settleprimarily from days, larvae 3.42). FortheshortPLDsof10-20 (Figure mortality scenario for theshortPLD,low larvae (Figure 3.41).For such asmall,isolatedsource,there is amoderateamountof retention of locally produced in theSECand southwestward is moved the othergroup into theSECCand entrainment Tonga TrenchEddy Table 3.3). Larvae fromontheyear,Rose splitintotwogroupsdepending one istransportednorthfor partial (Figure 3.11,pelago. DuetoitssmallsizeRoseisaveryminorcontributorthetotallarvalpoolofregion Rose Atoll (Motu O Manu or Muliāva by many locally) is a small island at the eastern tip of the Samoan Archi- Destinations page 83 Chapter 3 - Currents and Larval Connectivity page 84 Chapter 3 - Currents and Larval Connectivity larval mortality rates. Shadingoflabelsindicates coreislandgroups:red, American Samoa; green,Samoa.ND= no data. at) Rose from (arriving originating larvae of simulated sources) (and Figure 3.43.Destinations Atoll forlow,high and medium, This couldrefertoitspositionatoneendoftheSamoan Archipelago attheupstreamendofSEC. current”. the of “end as English to Samoan from translated be can “Muliāva” name used locally the note, Of tive tothelargesourcesoflarvaeproducedelsewhereinSamoanChain. rela- so farupstream and Islands by theCook provided sources larval in theSECfromsmall downstream 3.43). (Figure it issofar since in theregion from therestofislands of Rose theisolation This highlights days for PLDs of30-50 and to moderatemortalityscenarios in low to Rose butonly of larvae proportions only inscenarioswithlowmortality. Pukapuka to the east and Tokelau to the north contributemeasureable production for PLDs of and then 10-20 days.FortheseshortPLDs,Rosereceivesfewlarvaefromelsewhere Rose day PLDsarefromoutsidesources,whereas all larvaewith50-100 reliant onlocallarval Atoll isheavily on PLDanddailymortalityrate(Figure3.42).Nearly depending 0-100% ofitslarvaearrivingfromelsewhere Similar toManu’a,Rose Atoll isreliantonoutsidelarvalsourcesforaverywiderangeoflarvaerecruits,with Sources Wallis inthescenariowithlowmortality. of larvaetoalltheseamountsandislandswestviaSECcanevenreach cast smallproportions page 85 Chapter 3 - Currents and Larval Connectivity page 86 Chapter 3 - Currents and Larval Connectivity Position of virtual larvae from Swains Island for all model years by PLD. Upper and lower plots denote 3% and 18% and daily mortalityrespectively.3% denote plots lower and Upper PLD. by years model all for Island Swains from larvae virtual of Position Figure 3.44. Sw ains I slan d at thissitethat returnhere. produced larvae Percent ofsimulated at othersites.Bottompanel: produced settling atthis sitethatwere larvae Percent ofsimulated Island asafunctionof PLDandmortalityrate.Topat Swains retention supply and local larval Figure 3.45.Externallarval panel: toward PukapukaandNassauintheCookIslands(Figure3.44). (2004-2007) and consequently most of the larvae spawned there are entrained in currents flowing eastward 3.11,(Figure to theregion source larval major Tablein thecenterofSECCmostyears lies 3.3). Swains even moreas a larval source or destinationthansuggestedby distance alone.Dueto its small size,it is not a differentto theSamoan oceancurrentsrelative Archipelago. Swains of thesecurrentsisolates The position part ofthe the northern in atoll isolated Island isan Swains of very a region in lies EEZ and Samoa American Destinations page 87 Chapter 3 - Currents and Larval Connectivity page 88 Chapter 3 - Currents and Larval Connectivity larval mortality rates. Shadingoflabelsindicates coreislandgroups:red, American Samoa;green, Samoa.ND=nodata. Destinations (andsources)ofsimulated larvaeoriginatingfrom(arriving at)SwainsIslandforlow,Figure 3.46. medium,andhigh SECC fromtheseislandsareswepteastwardtowardstheCookIslandspriortoreachingSwains. islands of American Samoa are a significant source of recruits for Swains. Most of the larvae entrained in the arrive atfaroffthem all.Incontrast,noneofthe Swainsevenbeforethemoderatemortalityrateeliminates to west relative farther northand position and involved of larvae numbers can Samoa, somelarvae American proportion of the larvae from these sources are entrained in the eastward flowing SECC and due to the large seamounts. Wallisits even and and A Samoa of producers significant larvae major the from range PLD day the onlysourceforlarvaewitha10dayPLD(Figure3.46).Swainsreceivesmanyofitsin20-100 or dailymortalityrate(Figure3.45). Tokelau isthemainsourceoflarvaeforSwainsIslandandpractically of PLD regardless larvae of itsarriving 100% larval sourcesforvirtually on outside Island isreliant Swains Sources (Figures 3.13,3.44,3.46). and TaufilemuPasco reaching days 50-100 by seamounts and nearby days, and 20 Wallis after seamounts In 2008,allthelarvaefromSwainscanbeobservedmovingwestwardinSECwithmany considered. island other any than more Swains affected that condition a all, at forming not SECC flowing eastward the moderate mortalityscenarios(Figure3.46). In 2008 however, a dramaticallydifferent patternemergedwith larvae inthe20-50dayPLDcanrangemakeittoPukapukaandNassausuccessfullyonlylow long distancesthatmustbetraveledandthelownumberoflarvaestartingfromasmallsitelikeSwains,only Virtually nolarvaeareretainedlocallyatSwainsfor any PLDormortalityscenario(Figure3.45).Dueto the page 89 Chapter 3 - Currents and Larval Connectivity page 90 Chapter 3 - Currents and Larval Connectivity spawning dates tooccurat adifferentspawning timeofyear,be of theSECC would patterns intheregion connectivity the Samoan It Archipelago. isimportant to note that the SECC isastrong,buthighlyseasonalcurrent.Were settlement in successful to theSECforhighly the SECC connecting loops the feedback into enough quickly are notentrained and ocean lost totheopen are largely from Swains Larvae the rightconditions. SECC under end of their PLD. Only the large larval sources on the northern sides of Upolu and Savai’i reach Swains in the back into loop Rose between ocean in theopen or expire Samoa American at the Islands the Cook Atoll and either and of Swains swept south quickly system are current in theSEC-SECC entrained sources chipelago from therestofSamoan disconnected in thiswayandisthuslargely from Most larvae Archipelago. Ar- function to field current SECC the in north far too is Island Swains that demonstrate simulations the above, Despite the potential for circular transportinthe current loopsconnectingthe SEC and SECCas noted small size,contributerelativelylittletothelarval pool ofthe Archipelago. mounts of and, duetotheirvery on larvaefromelsewhere American Samoaarealmostentirelydependent sea- the and Island Swains Savai’i. and Upolu to relative production larval of levels moderate have Samoa populations. reef area,andthereforesmallerpotentialspawning Tutuila andtheManu’aIslandsof American the Samoan reef area. Movingeastalong potential are smaller,the islands Archipelago havelesspotential given theirverylarge overall the majorsourceoflarvaeforregion The islandsofSamoaareprobably matrices, especiallyevidentatshortPLDsandhighmortalityrates(Figure3.12). islands and should be managed accordingly. This is reflected in the interconnected “core” of the connectivity that muchoftheSamoan among transported of larvae sources on internal dependent is largely Archipelago suggest of larvae source from anyother large downstream distances the long currents and of thedominant Samoa and between planning resources andconservation ment ofmarine Samoa. American The orientation manage coordinated of benefits potential the demonstrate PLDs, different with organisms on based while with PLDsof30-100days. for organisms especially by this larvalconveyorbelt, established The connections as simulatedhere. for currents makeSamoaanimportantsourceoflarvae These feedback Samoa American in lateOctoberorNovember spawned the PLDsoforganisms throughout developed currents areoftenwell can Samoaviathe feedback loopsconnectingthe SECC withthe SECatW ~165-170º longitude. These of islands the along settle ultimately Ameri- can and SECC flowing east the in entrained are there produced for strongSECC. the seasonally The northcoastsof Samoa arefar enough west andnorththat many larvae 30 days. is formuch oftheyear,probably pattern, and be theextentofconnectivity That would it not were with shorterPLDsof10- for organisms to Samoaespecially production Samoa exportmuchlarval American to reefs andislandneighborsthewest. An overall effect tendencyisthattheislandsof of thisdirectional SEC. In general, larvaeproducedatanygivenlocationintheSamoan tend toseedtheirnatal Archipelago Current flow, and consequently larval transport, is primarily westward along the Samoan Archipelago via the connectivity, particularlyatshorterPLDsandhighmortalityrates. of patterns in evident clearly are flow current of ex- patterns predominant larval However,the of 3.12). rate (Figure change small some least at by interconnected are region the in sites all virtually low, sufficiently is mortality when and, PLDs longer for fact, In region. this in patterns flow mean strong the despite widely larvae spreading in role significant a plays diffusion turbulent that indicating destinations, and sources both Most sitesinthecentralportionofstudyregionarebroadlyconnectedtoawidevarietyotheras reef ecosystems Samoan of andmanagement (Craig andBrainard2008). theconservation for implications important have findings These Rose). (e.g. reefs other to sources significant be can destinations common particularly not are that tions areingeneraldependentonlarvalarrivalfrom external sources(e.g. Swains). Conversely, some sites in thesensethattheyarenotimportantsourcesforotherreefs,thesesameloca- some locationsareisolated The overallpictureisofsystem an inter-connectedinwhichnosinglelocationoperates inisolation. Although reef onoutsidesourcesevenattheshortestPLDsconsidered. of anyindividual of dependency some degree region, withsubstantiallarvalretentionat surrounding most locations, butalsosubstantial larvalexportand Our resultsindicate C oncl u sions a high but variable degree of inter-island connectivity in theSamoan connectivity of inter-island degree but variable a high and Archipelago - and Sponaugle 2009,Costelloetal. 2010). reduce multiple use conflicts and provide benefits to multiple stakeholder groups (Gaines et al. 2007, Cowen that strategies “win-win” identify to help can and goals economic and fisheries, conservation, of realization able, andasymmetricamong locations,as can improve is thecaseinthis region,integratedspatialplanning vari- is high, with othersites.Whenconnectivity linkages considering without location at asingle undertaken management areas,would be morelikelyto achieve management andconservationgoalsthan any effort effort,planning gests thataregional and conservation network ofmarine at thedesignofanintegrated aimed American Samoa. pattern oflarvalconnectivityintheSamoan inter-connected The highly sug- Archipelago from sources more modestlarval on therelatively primarily depend and would seeding Tutuilain and Manu’a regional MPA network. Were thesetwo sites disturbed, recoverywouldprobablybe slowdueto their highself resilient a devising when consider to important them make which Savai’i and Upolu from larvae on depend may in thearchipelago elsewhere larvae foritselfandtheentireregion.Recoveryfrom localizeddisturbance of source is animportant Samoa Swains, and of Rose status. Incontrasttotheisolation protection special for these sitesareworthyofconsideration uniqueness/isolation) and biogeographic tial followingdisturbance poten- recovery slower (probable the tripfromdistantsources.Forthesetworeasons of making are capable 4) may be apreponderance of either specieswithnopelagicdispersal, orspecieswithverylongPLDsthat (Tribolletstructure relativetotherestofarchipelago community Chapter et al.2010, Williams et al.2010, ing adisturbancedueto distinct a lackof recruits. Onereasonthesetwolocations haveabiogeographically the slowesttorecoverfollow sources andthusmaybeamong larval Island arefarupstreamfromanylarge bleaching, predator outbreaks (e.g. crown-of-thorns starfish) or disease. Sites such as pollution, Rosefishing, storms, Atollinclude andcould Swains that disturbances following ecosystem community,or population, a refers totherateofrecovery events, ornatural.Resilience tems todisturbancewhetheranthropogenic of reefecosys- for theresilience here haveimportantimplications The patternsofconnectivitydocumented ity andvariabilityinconnectivityisanotherattractivefeatureofwell-designedMPA networks. in oursimulatedconnectivity matricesunderthe right circumstances. Robustnessto the inherent stochastic- connect cellsthatareblank of larvae evenfromsmallsources,iftheyaretimedjustright,andcould numbers that deviatefromthosepredictedhere.Sucheventscouldtransportlarge patterns oflarvaldispersal unusual ticular timeperiod. current patternwillresultin that asingle,rare,anomalous There is alwaysthepossibility to predict, andthe patterns wehavedescribedhererepresentan accumulation of connectivity overa par- impossible events are dispersal but individual 5 yearperiod, representative of connectivityoverarecentand al. 2008).We havefocused oncumulativepatterns et (Siegel ocean turbulent a of fields current by en it isdriv- an inherentlystochasticprocessbecause is dispersal that larval to remember It isimportant larval sourcestobeginwith. the ocean, andbecausethe Cook Islandsaresmall the turbulentdiffusion that spreads larvaewidelyin of timeittakestogettheSamoan Archipelago, mortality,to reachSamoaduelarval thelength not verylikely from theCookIslandsareprobably PLDs with long Even organisms must betravelled. that distance Cook Islandssourcesduetothelong ganisms withshortPLDsfailto reach Samoafrom well connectedtoislandsintheSamoanchain.Or- group. These sitesarequitefarupstreamandnot the Samoan are intheCookIslands Archipelago The larvalsourcesupstreamintheSECfrom of theyear. needed to evaluate larvaltransportduringthe rest different.quite start datesare simulation Additional Image ProvidedBy:NCCOS. kilometers across,anisolatedend-pointalongtheSEC. Image 11. oftinyRose Satelliteimagery 3.6 Atoll, approximately - page 91 Chapter 3 - Currents and Larval Connectivity page 92 Chapter 3 - Currents and Larval Connectivity hydrodynamic modelsimulations. the NCCOS IT staff and our office neighbors for facilitating the use of the dozen computers needed to run the comments on thiswork.PhilWiles(ASEPA)helpful provided a draftofthiswork.Manythanksto reviewed and Pacific the in connectivity of study the for models provided has (NOAA/NMFS/PIFSC) Kobayashi Don and reviewofdraftsthereport. oftheapproach development commentsduring DMWR) providedinsightful moan for Archipelago manyyearsandinspiredmuchof the presentstudy. 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