Coral Reefs And Climate Change: Science And Management by Al Strong, Joanie Kleypas, JonathanT. Phinney, Ove Hoegh-Guldberg, and William Skirving


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Coastal and Estuarine Studies 61 JonathanT. Phinney,Ove Hoegh-Guldberg, Joanie Kleypas, William Skirving,and AI Strong (Eds.) Coral Reefs and Climate Change' Science and Management American Geophysical Union Washington, Publishedunder the aegis of the AGU Books Board Jean-Louis Bougeret, Chair;GrayE. Bebout,CarlT. Friedrichs, JamesL. Horwitz,LisaA. Levin,W. BerryLyons,KennethR. Minschwaner, AndyNyblade,DarrellStrobel,and William R. Young, members. Libraryof CongressCataloging-in-Publication Data Coral reefs and climatechange: scienceand management. p. cm. - (Coastalandestuarinestudies;61) Includesbibliographical references. ISBN-13:978-0-87590-359-0 (alk. paper) ISBN-10:0-87590-359-2 (alk. paper) 1. Coral reefsand islands-Environmental aspects. 2. Climatic changes-Environmental aspects. I. AmericanGeophysicalUnion. QH95.8.C67 2006 577.7'89-dc22 2006035298 ISBN-13:978-0-87590-359-0 ISBN-10:0-87590-359-2 ISSN 0733-9569 Copyright2006 by the AmericanGeophysicalUnion,2000 FloridaAve., NW, Washington,DC 20009, USA. Figures, tables, and short excerpts may be reprintedin scientificbooks and journals if the sourceis properlycited. Authorizationto photocopyitemsfor internalor personaluse, or the internalor personaluse of specificclients,is grantedby the AmericanGeophysicalUnionfor librariesand other users reg- isteredwith the CopyrightClearanceCenter (CCC) TransactionalReportingService, provided thatthe basefee of $1.50 per copyplus$0.35 per page is paid directlyto CCC, 222 Rosewood Dr., Danvers, MA 01923. 0733-9569/06/$1.50+0.35. This consentdoesnot extendto otherkindsof copying,such as copyingfor creatingnew collectiveworks or for resale.The reproductionof multiplecopies and the use of full articles or the use of extracts,includingfiguresand tables, for commercialpurposesrequirespermissionfrom the AmericanGeophysicalUnion. Printed in the United States of CONTENTS Preface JonathanT. Phinne3;Ore Hoegh-Guldbet2g, JoanieKleypas, William Skitying and Allan E. Sttzmg .......................... Corals and Climate Change:An Introduction JohnE. N. Veronand JonathanPhinney ......................... vii 1 Tropical Coastal Ecosystemsand Climate Change Prediction: Global and Local Risks Tert3'Done and RogerJones.................................. 5 Coral Reef Recordsof Past Climatic Change C. Mark Eakin and Andrda G. Gtz>ttoli ......................... 33 The Cell Physiologyof Coral Bleaching SophieG. Dove and Ore Hoegh-Guldberg...................... 55 Coral Reefs and Changing Seawater Carbonate Chemistry JoanA. Kleypasand ChrisLangdon........................... 73 Analyzing the RelationshipBetweenOcean Temperature Anomalies and Coral DiseaseOutbreaks at Broad Spatial Scales ElizabethR. Selig, C. Drew Hatyell, JohnF. Bruno, BetteL. ¾t,?llis, CathieA. Page,KennethS. Case); and Hugh Sweatman...................................... 111 A Coral Population Response(CPR) Model for Thermal Stress R. van Woesik and S. Koksal ................................ 129 The Hydrodynamics of a BleachingEvent: Implications for Management and Monitoring William Skitying,Mat Heron, and ScottHeron .................. 145 Identifying Coral BleachingRemotelyvia Coral Reef WatchImproved Integration and Implicationsfor ChangingClimate A. E. Strong,E Arzayus,W. Skirving,and S. E Het•n ............. 163 Management Responseto a BleachingEvent David Obura, Billy Causey,and Julie Church ................... 181 11 Marine ProtectedArea Planning in a ChangingClimate RodneyV. Salm, Tert3'Done, and ElizabethMcLeod .............. 207 12 AdaptingCoral Reef Managementin the Faceof Climate Change 10 Paul Marshall and Heidi Schuttenberg........................ List of Contributors ......................................... 223 PREFACE Theeffects of increased atmospheric carbon dioxide andrelated climate change on shallowcoralreefsaregainingconsiderable attentionfor scientificandeconomic reasons worldwide. Although increased scientific research hasimproved ourunderstanding ofthe response of coralreefsto climatechange, westilllackkeyinformation thatcanhelp guidereefmanagement. Research andmonitoring of coralreefecosystems overthepast few decades havedocumented two majorthreats relatedto increasing concentrations of atmospheric CO2' (1) increased sea surtktce temperatures and (2) increased seawater acidity(lowerpH). Higheratmospheric CO2levelshaveresulted in risingseasurface temperatures andproventobeanacutethreattocoralsandotherreef-dwelling organisms. Shortperiods(days)of elevatedseasurfacetemperatures by aslittle as 1-2øCabovethe normalmaximum temperature hasledto morefrequent andmorewidespread episodes of coral bleaching-the expulsionof symbioticalgae.A morechronicconsequence of increasing atmospheric CO2 is the loweringof pH of surfacewaters,whichaffectsthe rate at whichcoralsand otherreef organismssecreteand buildtheir calciumcarbonate skeletons. AveragepH of thesurfaceoceanhasalreadydecreased byanestimated 0.1 unit sinceproindustrial times,andwill continueto declinein concertwithrisingatmospheric C()2. Theseclimate-related stressors combined withotherdirectanthropogenic assaults, suchasoverfishing andp{>llution, weakenreeforganisms andincrease theirsusceptibility to disease. The economic ramifications of reducedor disappearing coralreefsare staggering: between10()and500 millionpeoplefrom 50 nationsdirectlydependon coralreefsfor food; while tottrismand fishingare multibilliondollar industries. Indirectservicesfrom c()ralreefs,suchasprotective barrierst:¾om waveactionandtsunamis, arealsoimportant, especiallysincesealevelis expectedto riscquickerin response to climatechange. Giventl•ebleakoutlookfor shallowcoralreefs,whatcannaturalresource managers do"? This b{)okattemptsto bridgethe scienceand management of coralreefsin the face of a changingclimate.It providesan overviewandbackgroundof the scientificissuesas well as present•lmnageme•ltstrategiesto limit the effectsof climatechange.The scienceof coral reefsandclimatechange,andresultingmanagement actions,will continueto evolve. The int'rmati{m in thisbookportraysthe urgencyto improvethe scienceandmanagement of coral reefs in a changingclimate as well as the necessarybackgroundint•mnation t() do so. The editorsthank the authorswho oraciouslyacceptedour invitationand submittedthe chaptersc{)mprisingthis publication.They are also indebtedto the many reviewersfrom the coral reel'scientificand managementcommunity- a small, but dedicatedlot- whose critiquesandcommentsgreatlyimprovedthe accuracyandclarityof the book.The financial supportfi'omthe NOAA Coral Programto offsetpublicationanddistributioncostsis gratefully acknowledged.Finally, the editorswish to acknowledgeour AGU acquisitions Coral Reefs and Climate Change:Scienceand Management Coastal and Estuarinc Studies 61 Copyright2006 by theAmericanGeophysicalUnion. 10.1029/61CE01 editor,AllanGraubard, andstaffmember,DawnSeigler,whopatientlysteeredthispublicationtowardscompletion. Jonathan T. Phinney,OveHoegh-Guldberg, JoanieKleypas,William Skirving andAllan E. Strong Coralsand Climate Change'An Introduction JohnE. N. Veron and JonathanPhinney Shallowwatercoralreefsare widely consideredthepinnacleof nature'sachievement in the Oceanrealm,for not only aretheyamongthemostbeautifulplaceson Earth,theyare thenexusof rnarinebiodiversity. Reefsaremorethanbiologicalentities,however;theyare geologicalstructures aswell - in fact,the biggestandmostenduringstructures evermade by life on Earth. This uniquecombinationof beauty,biology,and geologymakesthem immenselyvaluable.They headthe list of naturaltouristdestinations; providea livelihood for millionsof peoplespreadaroundcoastsof the tropicalworld;andare a rich sourceof pharmaceutically activecompounds. This is quite a list of superlatives,andthereare others.Being bothbiologicalandgeologicalentities,coralreefsleaveexceptional recordsof ancientmarineenvironments, and of thelife-formsthatonceoccupiedthem.Theserecordsaresetin limestone,a component of thecarboncycle- arguablythe mostimportantof all the Earth'sgreatbiogeochemical cycles.Carbondioxide(CO2) playsa criticalrolein the globalcarboncyclebecause it is a keycompound in photosynthesis, in thecarbonate bufferingsystemof theoceans, andin theEarth'sradiativebalanceof theatmosphere. Not surprisingly, changes in theamountof carbondioxidein ouratmosphere havemanydifferentandfar-reaching consequences for all reefs- past,present,andfuture. Coral reefsexistat the interfaceof the ocean,landandatmosphere. This dynamicrealm leavesreefsexceptionally vulnerableto environmental change.Coralsbuildreefsthatin turncreatethehabitatsthatallowthemto proliferateduringsealevelfluctuations. Tobuild thesemassivereefsin nutrient-poor(oligotrophic)oceanrealms,coralsmaximizetheir energysources by maintaininga symbioticrelationship with algae- zooxanthellae-that inhabittheirbodytissuesandprovidemostof theenergyfor coralgrowth.Thissymbiotic relationship requires a commitment tolivenearthesurface of warmtropicaloceans, which arethemostlikely areasto be affectedby atmospheric changes, includingchanges in temperatureandcarbondioxideconcentration. A centralconcern- andthe subjectof thisvolume- is whathappens whentheenvironmentbecomes lessthanoptimalfor coralreefecosystems, asis nowhappening because of increases in atmospheric carbondioxide.We knowthatthepresent increases aredueto anthropogenic activities, butwealsoknowthatincreased CO2levelshaveoccurred in the geological past,soa logicalquestion is:Whathappened to reefsduringotherhigh-CO2 periods? Beforeturningtothisquestion, wemustaddonefinalsuperlative toourlist:reefs,alone of all majorecosystems, havebeendecimated byall fiveof thegreatmassextinctions of CoralReefsandClimateChange:ScienceandManagement Coastal and Estuarine Studies 61 Copyright 2006by theAmerican Geophysical Union. 2 CORALS AND CLIMATE CHANGE: AN INTRODUCTION Earthhistory. In factthisis abouttheonlythingall fiveextinctions havein common. The timereefshavetakento recoverfrom massextinctionsis certainlyreal: 6 to as many as 13 millionyears;timeenough to buildtheGreatBarrierReefecosystem severaltimesover. Theseimmensetime intervals,nicknamed "reefgaps,"appearto be associated with high levelsof atmospheric carbondioxidein all butone(stillunclear)case.Thisis notto say thatcarbondioxidewasthecauseof pastmassextinctions, butthe association deserves furtherstudy.In thepast,several gases including cm-bon dioxidehavecomefromgeological sources suchas volcanism - primarilythe outcomeof sea-floorspreading- and exploding asteroid impacts. Thecarbon cyclehasalsobeeninfluenced by variations in solarirradiance dueto changes in solaroutputaswell asin theEarth'sorbitalgeometry around thesun,andby sudden releases of methane from(methane)hydrates storedin the deepoceanas ice slurries. Are suchdrasticchanges aboutto happenagain'? Giventhe rarityof massextinctions, thisseemsunlikely.Butbiologicalchangeis alsounpredictable, particularly because the responses of livingorganisms to largeenvironmental changes aregenerally nonlinear and likelyto occurasa seriesof threshold events.Coralsaretolerantto bothchanges in heat andwaterchemistry - up to a point.And it is possible to understand andpredictclimate change withindefinable boundsof uncertainty. Unfortunately, determining thesebounds of uncertainty is largelyderivedfrom the ongoingglobal"experiment"of rising atmospheric CO,_sinceourunderstanding of pastclimatechanges oncoralsremainssoincomplete.A loomingconcern for scientists andmanagers is whetheror notwe will understand andmanagetheseuncertainties beforemostof thepresentshallowreefsare gone. After theendof theCretaceous massextinction65 million yearsagoandthe beginning of ourera,the Cenozoic,therewereno living reefs.High levelsof carbondioxideand methane persisted, thenpeakedat the end of the Paleocene(55 million yearsago) in an event known as the Late Palaeocene Thermal Maximum. At this time, for reasons unknown,over 1,000gigatonnes of carbon,probablyas methane,were releasedinto the atmosphere in 1,000yearsor less.This amountsto 25-50% of the entireCO2 releasenow anticipated from humanactivities.The abruptreleaseis associated with a 5-7øC rise in deepoceantemperatures (asrecorded in sediments) anda dramaticshoalingof thecalcium carbonate compensation depth.If thiswasa rehearsalof what is happeningtoday,it is an interesting one,for peaklevelsof carbondioxideremainedin the atmosphere for over 100,000years. Globaltemperatures reacheda maximumduringEarly Eocene(50 million yearsago), then startedto decline.By Mid Eocene,carbondioxide levels were roughly similar to thoseof today.By Late Eocene,the first coolingcycleshad becomeclearly established: glaciershad formedon Antarctica.And after a gap of many millions of years,reefsonce againproliferatedaroundthe world.The environmental trail fadesat thistime but becomes clearagainin the EarlyMiocene(20 million yearsago).Sincethencarbondioxidelevels havebeenuniformlylow - below 360 ppm - and so havemost measuresof oceantemperatureexceptfor occasional short-termexcursions, mostlyfrom unknowncauses.The IceAge fluctuationsin atmospheric CO2that occurredthroughoutthe Pleistoceneand into theHolocene,roughlybetween200 and300 ppm,arefar lessthanprojectedC02 increases for this century(present-day concentration is alreadygreaterthan 380 ppm, and is projectedto at leastreach560 by the middleof this century). Masscoralbleaching-the mostimmediatebiologicalconsequence of globalwarming - hascausedwidespread degradation of reefs aroundthe tropicalworld.Yet this extraordinaryphenomenon hasonly beenknownfor two decades. Nothingis comparableto theseworldwidemassivebleachingeventsin humanhistory,at leastnotin the oceanrealm andnotasa resultof unintentional humancause.Alreadythe reasonsbehindthe VERON AND PHINNEY 3 arewellknown:increases in maximum seasurface temperatures arepushing corals beyond theirthermaltolerances andareparticularly widespread duringwmTnphases of theE1 Nifio-Southern Oscillation. Theresulting bleaching, caused by a breakdown in coral-algal symbiosis, is nowa regularevent.In addition, oceanacidification fromchanging oceanic bufferingcapacity hasbeenshownto slowcoralcalcification. Theconsequences of this phenomenon arestillunclear, butit is likelyto affectnotonlycoralsandothercalcifying reef organismsbut reef-buildingaltogether. By any standards, the plight of reefscomesfrom a strangechainof circumstances. Increases in atmospheric carbondioxidecomposition causethe Earth'satmosphere to warm, which in turn warms the upper ocean.This warm water causesa breakdownin coral-algalsymbiosis, andthe breakdown leadsto massbleaching. Manyof thelinkages betweencarbondioxide and coral bleachingseemimprobableat first. In this chainof eventsoccurenvironmental or physiological changes thatareeitherinvisible(e.g.,changes in atmospheric composition)or barely measurable(e.g., biochemicalchanges).Yet the effectsare real, andnow thereare soundexplanations for them. Not surprisingly,massbleachingeventshavesetoff numerousalarmbellsfor coralreef managersand scientists. Fifty yearsfrom now,for example,the Earth'spopulationwill haveincreasedapproximately by another3 billion.And evenif majorthirdworldcountries havenot adaptedfirst world living standards, greenhouse gas emissionswill almostcertainly be greaterthantheynow are. Fifty yearsfrom now we will alsohavea nmchbetter understanding of the responseof coralreefsto climatechange.Coralswill likely survive on thegeologictimescale,astheyhavein the past,butbasedon currenttrendsit is unlikely that coralreef ecosystems will improve,at leaston time-scalesrelevantto humans. This book thusprovidesa brief backgroundon the currentscienceand management optionsfor shallowcoralreefsin a changingclimate.There are two majorthreatsto shallow watercoralsfrom increasedatmosphericcarbondioxideconcentrations: increasedsea surfacetemperaturesand lowered pH (increasedacidification).Chaptersone through sevenprovidethe scientificunderpinnings of coralsandclimatechange.Chapteronesituatesreefswithin the largercontextof tropicalecosystems, includingmangroves and seagrass,with commentson the generaldeteriorationof ecosystemresilience.Chaptertwo providesan overviewof paleoclimatology, and the methodologies usedwhen describing chronologies of pastclimatechangein fossilcorals.Chaptersthree,four and five provide overviewsof the physiologicalandenvironmental effectsof increasedseasurfacetemperatures(chapterthree)and lower pH (chapterfour); andhow increasedtemperature may make corals more susceptibleto water borne pathogensand disease(chapterfive). Modellingis a criticaltool for managersand scientists towardunderstanding, andpossibly forecasting,coral vulnerabilityto increasedtemperatures; thus,chapterssix and seven providea physiologicalmodel and a hydrodynamicmodel,respectively, as a meansto predictthe vagranciesof thermalstresson surfacecorals.Chapterseightthrougheleven movethe readerintothemanagement realm,andoffera "toolbox"of management options. Chaptereightprovidesan overviewof remotesensing techniques to predictpossible areas of elevatedsea surfacetemperatureswhere bleachingalertscan be issued.Chapternine providescasestudiesfi'omtwo distincttropicalregions,KenyaandtheCaribbean,onhow to managea bleachingeventonceit occurs.Chapterten andelevensummarize morelong rangeplanningoptionsfor managers in thef'aceof climatechange,includingestablishing marineprotectedm'easto protectbiodiversityandmanagefor ecosystem resilience. The scienceand managementof coral reefswithin a changingclimateare relatively youngbut fast-growingdisciplinesthat befit the seriousness and urgencyof the issue. Applyingtechniques fromotherscientificdisciplines, suchasgenetics andremotesensing, arewell-established in coralreef scienceandofferincrediblyimportantinsights. 4 CORALS AND CLIMATE CHANGE: AN INTRODUCTION theapplication of technology requirestrainingscientists and managersto utilize it. This highlights a serious gapin coralreefscience andmanagement, in thatmostcoralreefsare in "developing" countries whilemosttechnology development is in "developed"countries. Increasing collaboration betweenscientists andmanagers, as well as betweendeveloped and developingcountries,is a simpleand provenmethodto transfertechnologyand increase capacity. Here,theissueisoneof resources, bothmoneyandexpertise, to address theproblem.In themeantime,coralreefscientists andmanagersneedto broadentheirown expertise to includesocialscience,economics, andan understanding of howto bestinform policymakingfromlocalto nationallevels.The nextgeneration of coralreef scientists and managers will likely be more astutein thesefields,but it is uncertainwhetherthem is enoughtime to reversethe downwardtrajectoryof coral reefs and to ensurethat future generations can experience a thrivingcoralreef ecosystem. This statementis a difficult wayto starta book,butgiventhepresentstateandfutureprojectionsof coralreefs,it is a necessary 2 TropicalCoastalEcosystemsandClimateChange Prediction' Global and Local Risks Terry Done andRogerJones 1. Introduction Coastalmarineecosystems occupyshallowcoastalwatersand extendup riversand acrosscoastallands to the normal inland influence of tidal seawaterintrusion [Allee et al., 2000]. In the tropics(Figure1), coastalecosystems arecharacterized morethananything elseby mangroves, seagrass meadowsandtropicalcalcareous reefs(i.e., coralreefsand corallinealgaeridges)- the rich, diverseandinterconnected enginesof marineproductivity for tropicalislands,coastsandcontinental shelves. Ourgoalis to consider theprospects for thesehabitatsin the relativelyshortterm of a few decades-astheirlocalenvironmental settingschangewith the changingglobalclimate.We focuson theresilienceof their definingandessential attributes, andtheirvaluesto humans[Holling,1973;McClanahan et al., 2002; Nystr6met al., 2000]. These habitatsare being exposedto seasthat are projectedto becomegraduallywarmer(Figure2A), deeper(Figure2B); lessalkaline (Figure 2C) and more productive[Sarmientoet al., 2004] than their presentstates [Kennedyet al., 2002].The extentto whichtheecosystems canaccommodate thesegradual changes in averageconditions is of greatimportance. So too arethe implications of changes in theintensityandfrequency of extremeevents,suchasstorms andprecipitation. The Intergovernmental Panelfor ClimateChange[IPCC, 200lb] calledfor improved understanding of regionaldifferences in the physicaldriversandchangein ecological functionof coastalsystemsas the basisfor developingappropriate adaptiveresponses, frommanagement of coastalfisheries andshoreline stabilization [Burkeetal.,2000]tothe designof networks of marineprotected areas[Salmet al.,200!' WestandSalm,2003]. 1.I. MangroveForests,SeagrassMeadows,Coral Reefsand Coralline Algae Ridges In geological terms,individual mangroves forests, seagrass meadows, coralreefsand corallinealgaeridgeshavegenerallyhadveryshorthistories of occupancy at theirpresent sites,(givensealevelwas120m loweronly20,000yearsago- Peltier[2002]).Onany givenshore,thecurrentrelativeimportance, extentandjuxtaposition of thesehabitats is largelya product of theparticularities of theirHolocene histories (last10,000years)and theinfluence theythemselves haveonlocalenvironmental settings. In theLesser Antilles, Coral Reefs and ClimateChange:Scienceand Management Coastal and Estuarine Studies 61 Copyright 2006by theAmericanGeophysical Union. 6 TROPICAL COASTAL ECOSYSTEMS AND CLIMATE CHANGE PREDICTION A F. . mangro vs •"•- • ringing e "• . ".'"•'•,EstuarJne an•//'• Fringing coral reef•• •• / _r•4.._.. ' ; "• .....• Seagrass Se•grass" •. • •ba• mangrove•• (• •: • in5y •rm Algal n•es 1in100 y - - •// • • surge ...... '" Figure 1. Tropical marine ecosystems.A. Global distribution of coral species diversity, from>500 (darkest)to <50 species(lighest).afterVeron2000. Tropicalmangroveand scagras.,, meadows havea similaroveralldistributionpatternbut muchlower speciesdiversity(mangroves --40species, seagrasses --60species.) B. Localvarietyin typesandsettingsof mangroves, seagrass meadows andcoralreefs.Alsoshownaresealevelat 20,000yearsbeforepresent(- 120 m), and thereachof 1 in 5, 20 and 100y floodplumesandthe I in 300 y ,orm surge.The frequency andreachof floodplume.,, andstormsurgesthatexceedspecificdamagethresholds will change as climate changes. 'forexample, AdeyandBurke[ 1977landMacintvreet al. [20011paintpicturesof the currentstateandjuxtaposition of coralreefsand algalridgesas dynamicongoingprocesses witha stronoHoloceneletotoy. •,'•hatis nov.'coralreefmayhaveoncebeenal•al ridee,and viceversa.In somesettings,Adey and Burke suggested that insufficientHolocenetime haselapsedto allow reefsand ridgesto grow into shallowwaters,while in others,it 1 2 3 5 Increase intemp(øc) B ........... _--• • ................................. =.................... •,•...... •.. •_'_,•_ .... :......................... -•, ...:_•....•.._:... . • 0.1 0.2 0.3 0.4 0.5 0.6 Sealevelrise(m) c ß k I 3.25 3.0 2.75 2.5 2.25 2.0 Aragonite saturation • Figure2. Tropicalmarineecosystems. A. Projected increase ill temperature b) 2100{busine, asusualHad 3). B. Projected sea-le,,el riseby 2100{business itsusualHad 3). C. Projected Aragonitesaturation stateby 2070.AfterGattuso et al., 8 TROPICAL COASTAL ECOSYSTEMS AND CLIMATE CHANGE PREDICTION Whererelatively younger reefshavedeveloped toseaward of olderalgalridgesthatdevelopedin theirpreferred strong waveareas in earliertimes,thewaveblocking caused bythe coralsleavestheridgenowdegenerating in calmwaters.Likewisein the vastmangrove expanses of northern Australia, theonlywayto deeplyunderstand theircurrentlocation, extent andspecies zonation istoconsider themasthelegacies of vegetation andsedimentaryprocesses thathavetakenplaceoverdramatically changing sea-level andfluvial-tidal energy balance histories oftheHolocene [Chappell andWoodroffe, 1994;Semeniuk, 1994]. Butasecological entities thatmustconfront rapid,anthropogenic climatechange, it may bemoreimportant toemphasise twothings:1)thatthebiological assemblages in all these system havehadtimefortheturnover of manygenerations of theirdominant organisms, and2), thattheyhavebeenexposed to relatively constant sealevelandbenignconditions of temperature andseawater chemistry for thelast6,000yearsor so[Woodroffe, 1992]. Thesystems mayhave'beenthere'in termsof someaspects of climatein thegeological past[Pandolfi, 1999],buthuman populations havecometo relyonthemastheyhavebeen duringthelastfewdecades. Wehavebenefited fromtheiroftennotappreciated contributionsto theproductivity of fisheries andto shoreline protection. Wehaveenjoyedthemas someof nature'smostscenicandfascinating landscapes, seascapes andplaygrounds. We haveunwittingly cometo rely on theirprimarybiogenicframework(aboveandbelow ground biomass in thecaseof mangroves andseagrass meadows; theskeletons of corals andothercalcifying organisms in reefsandalgalridges):it is theseframeworks thatprovidehabitatfor ourseafood, andprotectour shoresby accumulating andstabilizingsediments within and below the tidal zone. Biological connectivity withinandamongthesesystems is important. Eachof them occursin discretelittoralunits,andeachunit relieson criticallinkagesbetweenunitsof its sametype,comprising sources and sinksfor eachotherthroughlarval and biological exchanges of shared species. Whentwoor moretypesoccurcontiguous with oneanother, astheyoftendo,theyprocess sharedwaters,exchange particulate anddissolved organic matter[Alongi,1998],andtheirplants,animalsandmobilesediments canintermingle.In the Caribbean,the biomassof severalcommerciallyimportantcoralreef fish specieswas foundto be morewhenadulthabitatwerecloselyconnected to mangovesthanwhenthey werenot [Mumbyet al., 2004].To manageandprotectthe valuesandresources of these systems, we need,therefbre, to understand notonlytheirindividualvalues,buttheconnectivityandinterdependencies amongthem.As a contribution to buildinga synopticview,we havestructured thischapterby firstlookingat two unifyingconcepts (risk andresilience) andthenlookingat the effectsof differentclimatechangevariables(sealevel, CO,., temperature, pH) across thesystems. Finally,we focusbrieflyon thesystems oneat a time. 1.2. Threatsto SystemResilience Thesetropicalmarinehabitats havebeendeteriorating underpressures of humanmodificationandoverexploitation for centuries [e.g.,Pandolfiet al., 2003;Hugheset al., 2003]. Such direct humanpressuresstill dominatethe short-termoutlook for their extent, productivity andbiodiversity - threekey indicatorsof theirglobalwell beingandvalueto human society. 'Inthelonger term,increasing global climate change effects seem tocompounddirecthumanimpacts,andincreasingly dominateecologicaland socio-economic change overthe21stCentury. Paleo-ecological andecological evidence showsthatthese ecosystems havepersistedin placeas recognisable entitiesthoughpastclimatechange [Pandolfi,1999].The threatthathumanactivitiesposeto ecosystems is in largepartreductionof the ecologicalresiliencethatunderpinstheirpersistence asproductive,diverseand usefulassemblages [Loreauet al., 2001; Bellwoodet al., DONE AND JONES 9 Foreachsystem, a keyaspect of theirecological resilience isthecapacity forthestructurallydominant organism - beit a standof mangrove, seagrass orcoral- torepeatedly reinstate itselfasthedominant structural formin thefaceof repeated disturbance. Thisis the basisfor eachparticularplaceto retainits identityandvalueto humansin thefaceof damage,destruction,erosionand resourceextractionthat are, or havebecome,a normal partof theirexistence. It is thecapacity for individual placesto restore theirpriorattributesof productivityand architecturalstructurein periodsof yearsto decadesbetween major disturbances that has madetheseplacesso valuableas habitatsfor fisheriesand wildlife,protectors of shorelines, buildersof beaches andislands,placesof greatbiodiversityandbeauty,andassetsfor tropicaltourism[McManusandPolsenberg, 2004]. For mangroves,seagrass meadows,coral and corallinealgaereefs,sea-levelrise and increases in oceantemperatures will potentiallyaffectlocal survivorship, extentof individualformations andregionaldistributions. Increasing concentrations of atmospheric CO2 will directlyaffectplantproductivity andindirectlyaffectgrowthratesin calcareous organismssuchas corals,clamsand calcareous macroalgae, potentiallyimpedinga reef'sability to growverticallyin pacewithsea-level rise.Thegreatertheclimatechange, thegreater the potentialdetrimentaleffecton humans,throughthe lossin areaof productive habitat, andlossof ecosystem goodsandservices in areasthatremain.Summaries of potentialhazards,consequences andrisk modifyingt2ctorsareprovidedin Tables1, 2 and3. Thereare two mainpurposesfor thischapter.The first is to describepotentialclimate changeeffects,and the secondis to addresstheir likelihoodof occurrenceat local scales. IPCC [2001a]providesa seriesof regionalassessments, but in relationto coralreefsand relatedsystems,eachtropicalregion'schaptermoreor lessreiteratesthesamecriticaloutcomes.We describea processfor assessing the likelihoodof exceedingcriticalthresholds at the local scale,by takinginto accounta) how physicalhazardsmaychangeunderclimatechange,andb) whichproperties of an ecologicalsystemanditslocalgeographic setting exacerbateor ameliorateits vulnerabilityto thosehazards. 2. Risk Assessmentand Risk Managementfor CoastalSystems The impactsof global changewill vary greatlyfrom place to place,requiringlocally appropriateadaptiveresponses by plannersandpolicymakers. A focuson localscales-say a bay, beachor provinceover which a resourcemanageror politicianhas influencebringsinto play major issuesof uncertaintyaboutthe potentialimpactand the adaptive response required.As in weatherforecasting, precisemediumto long-termpredictions for particulartimes and placesare unworkable.Howeverprojectionsmade within a risk assessment andrisk managementframeworkcanguidehumanadaptations to limit harmin an environment of uncertainty. Risk analysisis theprocess of assessing the likelihoodof a harmful outcome,while risk managementaims to reducelikelihood,consequences, or both.For example,mitigationof greenhouse gasesreduces the likelihoodof a givensetof a risein sealevel,whilebuildinga seawall reducesitsconsequences. Thisriskframework can help societyunderstand and makedecisionsaboutthe trade-offbetweenthe relative costsandbenefitsof adaptingversusthecostsandbenefitsof radicalchanges in thewaywe generateenergyandusefossilfuels. Climatechangerisksto tropicalcoastalecosystems can be considered in termsof the probabilityof exceeding criticalthresholds [afterPittockandJones,2000].Thisis a more tenableobjectiveat presenttryingto assignprobabilities to particularmodelpredictions. Our frameworkfor risk analysisis presented in Figure3 wherea cumulative probability curveconnectsthe 100% certaintyof exceeding'no change'andthe 0% likelihoodof exceedingthe 'highestchange'scenario.In ourhypothetical example,therearetwo 10 TROPICAL COASTAL ECOSYSTEMS AND CLIMATE CHANGE B. Lo(;al risk A. Global projections PREDICTION C. Thresholds Maximum ß (n High.• T2 t Copingrange 2 __T_t._3_ __M_•.o_r _c_o.s_t ........ L3 __T2._2__ _M_•_q_"•_•_•_t ......•--- __T_t._t_•_•_ø_r_•_ø.•.t ........•--- TI.0Neghg•ble,,cost ß[ . Zero 2000 2020 2040 2060 2080 2100 Year 0 25 50 75 100 Probabilityof exceeding projected increase Figure 3. Relatingthresholdexceedanceto the likelihoodof climate change.A. Rangesof increaseof hypothetical climatevariablessuchas CO2, sea-levelor seatemperature,showing twocriticalthresholds for onsetof effectsdetailedin C. B. Cumulativeprobabilitydistributions castas likelihoodof exceedance of any projectedlevelof increasein partA. L1 represents the globalmeanprobability,L2 a localein whichlocalgeographyameliorateschangein theclimate variableof interest,and L3, a localein which it exacerbates global change.These probability distributions - thatcombinetwo rangesof uncertainty,randomlysampledand multipliedin a mannerconsistent with Schneider[2001], are typicalof thosewith two or more component rangesof uncertainty. of changeandtwocriticalthresholds (Figure3A). The cumulativeprobabilityof exposure is givenin Figure3B. A criticalthresholdis definedasthe levelexceedinga tolerablelimit of harm.In the example,thereis an 80-100% probabilitythat the low threshold(T 1) will be exceeded.At thehigherrate of globalchange,it will occurby 2015, and at the lower rate,by 2060. For the highthreshold(T2), the oddsare lower (5-30%) and theycomeinto play around2080. In eachcase,the rangein the oddsis largely a functionof local circumstances (Figure3B) that ameliorate(L2) or exacerbate(L3) the hazardcomparedto theglobalmeanhazard(L1). Applicationof this approachto any real systemrequiresthat we addressfour main issues: uncertainties in climatechangeat globalandregionallevels(encompassing global climate modellingand downscalingissues);the formulationof critical thresholds;attributesof the localphysiographic and environmental settingsthat modify the likelihoodof critical thresholdsbeing exceeded;and intrinsicattributesof the local ecosystemthat determinethe extent to which it accommodates,is damagedby, or benefits from, the changedconditions. 2.1. Uncertainties in Global Climate Predictions The uncertaintyin globalclimatepredictionsis causedalmostequally by uncertainty aboutfuturegreenhouse gasemissions anduncertainclimatescience[Pitrocket al., 2001]. This uncertainty, embodiedin the familiar SpecialReporton EmissionScenarios(SRES) envelopes of diverging 21stCentury trajectories forrisesin CO2,temperature andsealevel, is caricatured in Figure3A. The IPCC [IPCC, 200lb] explicitlydoesnot assigna DONE AND JONES 11 likelihoodto the differentemissionscenarios[Nakigenovicand Swart,2000: Schneider, 2001]. Despitecontinualimprovements in globalclimatemodels,their assumptions and predictions aregenerallynotvalidat regionalscales[Murphyet al., 2004].Nevertheless, asPitrocket al. [2001] observed, we canbe surethatthecumulative probability of exceeding anyparticularleveldoesdeclinewith increasing magnitude (Figure3B). 2.2. Critical Thresholds Criticalthresholds are delimitedat their upperandlowerlimitsby thecopingrangeand ecologicalcollapse,respectively. The copingrangeof a system(Figure3C) represents a degreeof changesoslightthatit imposes no diminution on ecosystem functionality, and no costto the localdependanthumanpopulation.Copingranges1 and2 cansimplyrepresentecological/human systemswith smallerandlargercapacityto accommodate environmentalchangebeforenon-negligible costsareinflicted.(Alternatively, a copingrange couldrepresent the lossthatan authorityis prepared to accept,beforereacting). Coping rangeI couldbea changethatfallswithinnormalenvironmental andecological variability at thatsite,butthatmayhavepreviously beenexceeded undertheinfluence of extreme naturalevents(e.g.,pastfloods,droughts,heatwaves, storms).If globalclimatechange increases the frequencyof exposure to suchhazards,CopingrangeI is breached more oftenandby a greateramountandgreaterecological costsareimposed (T1.1to T1.3).An extremeeventsuchasa I in 1000y stormcouldprecipitate ecological collapsein a single step,or theremaybe a stepwise breakdown of homeostatic mechanisms of ecological resistance,tolerance and resilience (Table 1). TABLE1. Stages ofecological deterioration: resistance, tolerance, resilience andcriticalfailure. Thisterminology is intended fortheecological assemblage, nota dependent human population. Resistance (Tn.0)- theupperlimitto thecopingrangeof theecological systemis characterized byabsence of physiological symptoms orof change in lifeexpectancy for existingindMdualsand newcohorts: Tolerance (Tn.1) is theaccommodation of minorchanges to thevigouror life expectancies of keyfunctional species (suchasdominant species of mangroves, seagrasses andcorals) withoutlossof extent, productivity orbiological diversity of thearea.Biological adaptations developed asresponses to thesechanges mayincrease Tn.1 relative toclimate hazards, whereas repeated and/orcumulative stresses maydecrease it. Resilience(Tn.2- whosedistinctiont¾om•tolerance'is somewhatfuzzy) is thecapacity fortheecological assemblage torecover expeditiously, should thesystem bedamaged by anextreme event.It is theproperty thatensures that,in spiteof a temporary setback, there arenolasting changes infunction, composition and/or amenity tothehuman population. ('Expeditious' and'lasting' relate to •reasonable expectations' tk)ranecological system of a particular typeina particular place). Such resilience ischaracterized byspeed, strength andreliability intheprocesses ofrepair, recolonisation andnewgrowth. It isasmucha property of a damaged site's connectivity to,orisolation fromsources of supply oflarvae ofkeyfunctional groups andresource species, asit isofthelocalenvironmental conditions. Criticalfailure(Tn.3}signifies lossof resilience, wheretheecosystem losesits fundamental functionandattributes (suchasreef-building capacity in coralreefs; physical structure andhabitat roles of mangroves andsea-grass meadows). It could also occur directly asa single catastrophic event, such :rsphysical removal ofanunderlying sedimentary depositby a stormor a 12 TROPICAL COASTAL ECOSYSTEMS AND CLIMATE CHANGE PREDICTION 2.3. RegionalVariabilio'andLocalModificationof Environmental Change Globalclimatemodels(e.g.,Figure2A-C) showthatoddsof a regionexceeding a par~ ticularthreshold will notnecessarily bethesameastheglobalodds(L1 in Figure3B).This regional variability isaveraged outin theglobalcumulative probability of exceedance curve (L1 in Figure3A). Goingdownscale,thelocalcumulative probability curves(L2 andL3) area functionof localoceanography andlocalphysiography of coastalland-andseascapes. Forexample,'localoceanography' couldon theonehand,be a reliableupwellingsystem thatprevents localreefwatersfi'omheatingby a particularamount- say 1øC (L2), or on theother,a calmshallowareawherewarmingis exacerbated (L3). 'Localphysiography of the coast'couldbe a particularcombination of embaymentand bathymetrythat greatly lessens (.L2)or increases (L3) theoddsof exposureto a 0.5 m sea-levelriseor 1øCheating. 2.4. bztrinsicAttributesof the Local CoastalSystem TI andT2 (Figure3A) indicatelocaldifferences in the amountof change(e.g.,degrees of heatingor centimetres of risein meansealevel)thata coastalsystemcanaccommodate withoutanydetrimental effect.Examplescouldincludethe coralbleachingonsetthreshold (in degreesabove'normal') in a poorly adapted(T1) or betteradapted(T2) coral community, or thesea-levelrisethatwill inundatelower(T 1) or higher(T2) coastalinfrastructure. In otherwords,particulartypesof mangrove,seagrass or coralassemblages may havedifferentcopingthresholds (Tn.0) andcostthresholds (Tn.0 toTn.3)thatwouldhave beendetem'dned by the recentenvironmentat the site.For example,T1 may characterize a systemexposedhistoricallyto a relativelynarrowrangeof temperature andtide, andT2, a placehistoricallyexposedto muchgreatervariabilityin temperature andtide. 2.5. Local RiskAnalysis- a Coral Reef Example Coralbleaching(discussed in moredetail below) is a potentiallyfatal stressresponse thatbeginsas a sub-lethalpalingand whiteningof coralsthat occurswhen local summer seasurfacetemperature risesto localthresholdT1.0, whichis typically1-2øCabovethe locallong-termmeansummermaximum[GoreauandHayes, 1994]. The driver for coral bleachingis not the mean temperaturepet' se, but rather runs of extremely hot days [Berkelmans, 2002].Localtemperature thresholds cannevertheless be represented in relation to projectedincreasein global means(G in Figure4A) assumingthere is a proportionalincreasein •giona! meansand local extremes.For a nearshorereef in the central GreatBarrierReef (GBR), Jones[2003] obtainedthe projectedregional•neanout to the year2050 by extractingthecentralGBR trajectory(the averageof eightGCMs). He then superimposed local extremeson that trajectory,basedon an instrumentalrecordof daily temperature variabilitycoveringthe decadeof the 1990s,and identifiedthree thresholds, basedon observations andmeasurements from bleachingeventson the Great BarrierReef in 1998and2002:T1 (non-lethal bleaching); T1 + 0.5øC whichkillsthemostheat-sensitive corals;andT1 + 2.5øC, whichkills themostheat-resistant corals.By examiningthe intersections betweenthethreshold lines(Figure4C), theregionalwarmingcurveexcisedfrom a GCM, (Figure4A), andtheregionallikelihoodcurve(R in Figure4B), he concludedthat thisregionalaveragetrajectoryhasa 95% probabilityof exceedingthethresholdthatkills heat-sensitive coralsby 2015, and an 80% probabilityof killing heat-resistant coralsby 2040.Howeverin thesesameyears,thepredicted localwarmingatL1 wasonly70% to DONE AND JONES 13 B. Likelihood A. Global projections C. Thresholds 7 , 2000 2025 2050 2075 2100 0 25 Year .•.•T1.2 Death otrobu spp. .. T1,1 Death ofsensittve spp. 50 75 100 Probabilityof exceeding projectedincrease Figure4. Application of riskassessment framework to a coralreef.A. Mostlikelyglobalwarming curve (mean of 8 models).B. Thresholdexceedenceprobabilityfor globalwarmingcurves (G) andfor a coralreefat MagneticIsland,GmatBarrierReef,in whichrateof wanuingis slower thanglobalratedueto localgeographic setting.C. Illustrative thresholds for coralmortality. 100 ................. 80 eo '•->' 4øFø'5øc/•+1'øøc 7•'c• 0 0 1 2 3 4 Warming oC Figure5. Probabilities of localwarmingin 2030and2070superimposed on bleaching and mortalityrelationships for MagneticIsland,GreatBarrierReef.Probability for exceedance of bleaching thresholds is expressed astheannualriskat a giventemperature abovea 1990s baseline. of predicted regional warming. Thismeans thatthelocalprobabilities aresomewhat lower, andthe year of exceedance, somewhat later. An alternatepresentation of theserelationships (Figure5) predictedbleaching levels that were consistentwith observationsin recent years. At current 14 TROPICAL COASTAL ECOSYSTEMS AND CLIMATE CHANGE PREDICTION (i.e.,warn-ting = 0øCin Figure5), theannualprobability of a bleaching eventisjust over 40%(or4 events perdecade). Theannualprobability of bleaching +0.5øCis -•30%(3 per decade) andbleaching +I.0øC is <10%(<1 eventperdecade). With a IøC warming(70% likelyby 2070),thesefrequencies increase to 9, 6 and1perdecade. SiteL1 projected temperatures are70-80%of globalprojections, soto keeplocalwarmingat siteL1 belowthe critical0.5øCthreshold, globalwarmingwouldneedto bekeptbelow0.6øC. 3. CoastalMarine SystemsandTheir Environment Withtheriskmodelof Figure3 in mind,we nowconsider potentialimpactsandinteractions of a number of aspects of globalchange,potentially leadingto theexceedance of criticaldamagethresholds (e.g.,T l.3 in Figure2, whereresiliencecapacitycollapses). Laterin thischapter, we consider localattributes of sites,settingsandhabitatsthatmay ameliorateor exacerbate local hazardscomparedto the global averagefor a seriesof ecosystems. 3.1. RisingSeaLevel A mean global sealevelriseofbetween 90and880mm(about 1to9 mm.y -•) isprojectedfor the2l"t Century, thehugerangereflectingboththe uncertainties aboutfuture emissionsandthe inexactscience[IPCC, 2001]. Rising sealevel is clearly of major concernin coastalsystems, andthecommonest predictions areof floodingandcoastalerosion [CarterandWoodroffe,1994].Sedimenterosionfrom oneplaceanddepositionin another is theessenceof shorelinemorphodynamics, and,irrespective of climatechange,a matter of criticalimportance in relationto both humaninhabitation of coastalareas,and the integrityand valueof ecologicalassemblages that occupythoseshores.With climate change,regionalsealevel(Figure2B) will likely continueto risefor centuriesdueto the thermalinertiain theoceans.Locally,the key variableswill be meansealevel riserelative to the land surface,the seafloor and/orthe reef top, and the heightsof wave set-upand storm surges. For mangroves, risingsealevelwill potentiallyaffecttheir capacityto retaintheir substratumat a ratethatkeepspacewithsealevelrise[Twilleyet al., 1996].Woodroffk[1992] considers thatlower rates ofrise(<1mm.y -•) would havelittleimpact, butthathigher rates (5-8mm.y -•) willprobably besustainable onlyin settings withampleautochthonous sediment.For somesettingsand speciesassemblages, there is the prospectof mangroves advancing acrosslowlands,whilein others,theywill disappear assubstrata areerodedaway [Ellisonand Farnsworth,1996; Bacon,1994; also,seebelow]. Where the sedimentremains in placebuttheedaphicconditions andimmersionregimechange,infaunalandmicrobial communities will changewith consequences for theirrolesin the processes of decomposition,recyclingandsequestration of organicmatter[Alongi,1998].Snedaker[1995] stresses theimportance of localrainfallregimein the likelihoodof subsidence. Subsidence occurs whenratesof decomposition of sedimentorganicmatterexceedratesof production. This is likelywith reducedrainfallandrunoff,becauseit causeshighersalinity,greaterseawatersulfateexposureanddecreased production.Sedimentelevationswouldbe maintainedin placeswithhigherrainfallandrunoff,whichwouldresultin reducedsalinity,reducedexposureto sulfate,andincreased ratesof deliveryof terrigenousnutrients. Likewisefor coralreefsit is possibleto envisagenetgainsin somesituations.Evenslow growingindividualcoralsin shallowreef areascan grow verticallyfasterthan the

Author Al Strong, Joanie Kleypas, JonathanT. Phinney, Ove Hoegh-Guldberg, and William Skirving Isbn 9780875903590 File size 5.5 MB Year 2006 Pages 436 Language English File format PDF Category Biology Book Description: FacebookTwitterGoogle+TumblrDiggMySpaceShare Published by the American Geophysical Union as part of the Coastal and Estuarine Studies, Volume 61. The effects of increased atmospheric carbon dioxide and related climate change on shallow coral reefs are gaining considerable attention for scientific and economic reasons worldwide. Although increased scientific research has improved our understanding of the response of coral reefs to climate change, we still lack key information that can help guide reef management. Research and monitoring of coral reef ecosystems over the past few decades have documented two major threats related to increasing concentrations of atmospheric CO2: (1) increased sea surface temperatures and (2) increased seawater acidity (lower pH). Higher atmospheric CO2 levels have resulted in rising sea surface temperatures and proven to be an acute threat to corals and other reef-dwelling organisms. Short periods (days) of elevated sea surface temperatures by as little as 1–2°C above the normal maximum temperature has led to more frequent and more widespread episodes of coral bleaching-the expulsion of symbiotic algae. A more chronic consequence of increasing atmospheric CO2 is the lowering of pH of surface waters, which affects the rate at which corals and other reef organisms secrete and build their calcium carbonate skeletons. Average pH of the surface ocean has already decreased by an estimated 0.1 unit since preindustrial times, and will continue to decline in concert with rising atmospheric CO2. These climate-related Stressors combined with other direct anthropogenic assaults, such as overfishing and pollution, weaken reef organisms and increase their susceptibility to disease.     Download (5.5 MB) Sounding the Limits of Life: Essays in the Anthropology of Biology and Beyond Coexistence: The Ecology and Evolution of Tropical Biodiversity Algae: Organisms for Imminent Biotechnology Handbook on Cyanobacteria Plant Physiology (Biology Collection) Load more posts

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