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Mapping marine diversity �

issue 84 Dec 2006

Mappingmarine diversityHabitats are keys to conservation managementAlix Post, Ted Wassenberg (CSIRO Marine and Atmospheric Research), Vicki Passlow

Australia’sExclusiveEconomicZonecoversovertenmillionsquarekilometres,significantlymorethantheareaofitslandsurface.TheAustralianGovernmenthasmadeacommitmenttoassignaproportionofthisasmarineprotectedareas(MPAs).TheMPAsaretobedesignedtoprotectandpreserverepresentativesamplesofmarinebiodiversity.

However,ourknowledgeofmarinediversityandthedistributionofmarinebiotaisextremelypatchy.Biologicalsurveysarecontinuallydiscoveringspeciesthatarenewtoscience.Recentexpeditionsinthedeepoceanhavefoundthat,amongsamplescollectedatdepthsofmorethan3000metres,abouthalfthespecimensbelongtonewspecies(Schrope2005).

EvenwithinAustralia’sexistingMPAs,ourknowledgeofthedistribution,abundanceanddiversityofmarineorganismsremainssparse(e.g.southeastregionMPAs;Harris,inpress).Thelackofbiologicaldataisaseriousimpedimenttotheaimofselectingforprotectionsitesthatarerepresentativeofthetotalmarinebiodiversity.

Figure 1. GeomorphicfeaturesacrosstheNorthernPlanningRegion,andwithinthestudyarea,withsampleareasshownbythepinkdots.Theinsetsshowmultibeambathymetryimagesanddetailedgeomorphicfeaturesintersectedbythesamplesites.

Mapping marine diversity �

issue 84 Dec 2006

Defining habitatsAnalternativetothespecies-basedapproachtoconservationistheprotectionofmarinehabitats(e.g.ZachariasandRoff2000).Marinehabitatscanbedefinedonthebasisofphysicaldatasets,suchasthemorphologyoftheseabed,thewaterdepthandthesedimentproperties.Thisapproachissimilartothewayinwhichforesttypes(orbiomes)onlandaremappedbasedonknowledgeoftheslope,aspect,climateandsoiltypes.

Physicalparameterscanbemeasuredmuchmorequicklyandacrosswiderareasthanbiologicalinformation,providingarapidassessmentofmarineecosystemsthatcancontributesignificantlytotheselectionandongoingmonitoringofMPAs.ThishabitatapproachisbeingincreasinglyemployedinthemanagementofmarineareasinCanada,NewZealand,SouthAfricaandtheUnitedStates,aswellasinAustralia.

Thesuccessfuluseofphysicalparametersasasurrogateforspeciesdiversityanddistributionsdependsontheselectionofrelevantphysicaldatasets.Althoughanincreasingnumberofstudiestesttherelationshipsbetweenbiologicalandphysicaldatasets,broaderenvironmentalassociationsarestillpoorlyestablished.The

Figure 2. Thesixtaxawiththehighestabundanceacrossthestudyarea:A)polychaetetubes;B)brittlestars;C)aspeciesofbryozoan;D)aspeciesofhydroid;E)crinoids;andF)aspeciesofhearturchin.PhotoscourtesyofTWassenburg.

A

B

C

D

E

F

“Physicalparameterscanbemeasuredmuchmorequickly...providingarapidassessmentofmarineecosystems”

MorphologyAverage

depth (m)Seabed

exposure Grain Size Dominant fauna

Shelf 14­–35 Mod Sandy Prawns

SeaUrchins

Valley 37–4­3 Max Sandygravel Bryozoans

Brittlestars

Crinoids

Bryomol Reef 27–36 Max Sandygravel Brittlestars

Hydrozoans

Bryozoans

Talus slope 38–4­3 Mod–High Sandy Anenomes

Reef platform 27 Mod–High Sandygravel Ascidians

Octocorals

Reef margin 4­8–4­9 Mod–High Sandymud Crinoids

Sponges

Basin 51–65 Low–Mod Sandymud Polychaetes

Table 1. Characteristicsofdifferentbenthichabitatsandassociatedfaunas

Mapping marine diversity �

issue 84 Dec 2006

environmentalassociationsstudiedtodatevarygreatlybetweenregions,organisms,scalesandapproaches(e.g.Thouzeauetal1991,Kostylevetal2001,Ramey&Snelgrove2003).DetailedtestingwithintheAustralianregionishelpingtorevealwhichphysicaldatasetsbestdescribethedistributionofseabedbiotaindifferentsettingsaroundtheAustralianmargin.

Mapping biota in the Gulf of CarpentariaRecentresearchintheGulfofCarpentaria,northernAustralia,hasprovideddetailedphysicalandbiologicaldatasets,whichwehaveusedtotesttherelationshipsbetweenphysicalhabitatsandthedistributionofseabedcommunities.Samplinganddetailedbathymetrymappinghaverevealedarangeofphysicalhabitattypes,includingreefs,plateaus,valleysandshelfenvironments(Heapetal2006;figure1andtable1),alongwithdistinctiveseafloorbiotaassociatedwiththesedifferentfeatures.

Atotalof569specieswerecollectedontheresearchvoyage.Thesixtaxawiththehighestabundanceacrossthestudyareaare

polychaetes(tubeworms),brittlestars,aspeciesofbryozoan,aspeciesofhydroid,crinoids,andaspeciesofhearturchin(figure2).Ofthese,thehearturchinspecieshasthehighesttotalabundance,whilethespeciesofbryozoanandhydroidhavethebroadestdistributions.

Arangeofphysicalvariablesweretestedagainstthespeciesdatatodeterminewhetherstatisticallymeaningfulrelationshipscouldbeestablished,whichcouldallowbetterpredictionofspeciesdistributions(seePostetal2006).Thisanalysisrevealedthatthedistributionoftheseabedbiotacanbebestpredictedinthisregionbasedonacombinationofphysicalvariables,includingthesedimentcomposition(mudandgravelcontent),sedimentdisturbance,theseabedmorphologyandwaterdepth.Therelationshipbetweenthesevariablesandtheseabedbiotaisillustratedinfigure3acrossthesevenmaingeomorphiczones:shelf,arelictbryozoan–molluscbuiltreef(bryomolreef ),valley,talusslope,reefplatform,reefmarginandbasin.

TheshelfzonewithinthesoutheasternpartoftheGulfischaracterisedbyshallowdepths(15to30metres)withmoderateseabeddisturbanceandsandylowcarbonatesediments(figure3).Thefaunainthisshelfzoneisdominatedbymobileorganismswithrelativelylowdiversity,withprawnsandsea

Figure 3. RelationshipbetweenphysicalpropertiesandbenthicbiotainthesouthernGulfofCarpentaria.Forafulldescriptionofthekeybenthicbiotaandexplanationofsymbols,refertotable1.

“RecentresearchintheGulfofCarpentaria,northernAustralia,hasprovideddetailedphysicalandbiologicaldatasets”

Mapping marine diversity �

issue 84 Dec 2006

urchinsmoreabundant.Thebasinenvironmentisalsodominatedbymobilefauna(predominantlypolychaetes)withmediumdiversityand,becausethewaterisdeeper,haslowtomoderateseabeddisturbancewithmuddysandsediments.Thebryomolreefandvalleyenvironmentslieatdepthsintermediatebetweentheshelfandbasinzones(25to39metresand37to4­2metres,respectively),withveryhighseabeddisturbance(maximumvalues),particularlyacrossthevalleyarea,andagravellysandseafloor.Thefaunasassociatedwiththesetwozonesarecomposedofequalabundancesofattachingandmobileorganisms,withthebryomolreefdominatedbybrittlestars,hydrozoansandbryozoans,andthevalleyfaunasbybryozoans,crinoidsandbrittlestars.

Themodernreefenvironmentisdividedintothreedistinctzones,eachwithamoderatetohighseabeddisturbance(figure3).Thetalusslopeissandywithhighcarbonatecontent,andthepresenceofripplesindicatesstrongbottomcurrents.Thesecharacteristicsareassociatedwithlowfaunaldiversitydominatedbysolitaryanemones.

Figure 4. Distributionoffivehabitatclustersderivedfromthepercentageofgravelandmud,thewaterdepthandtheseabedexposureforpartoftheNorthernPlanningArea,withgeomorphicunitsshownbythegreyoutlines.ThesoutheasternandeasternpartsoftheGulfandTorresStraitarepartofclusters1,2and3,whilethecentralandwesternGulfandthewesternArafuraSeaarecharacterisedbyclusters4­and5.Substrateclustersoccurwithindifferentgeomorphicfeatures,illustratingtheimportanceofcombiningthesedatasets.

Thereefmargin,bycontrast,iscomposedofmuddysandsediments,reflectingthelowerenergyofthisarea.Thesefeatureshaveproducedhighfaunaldiversity,withcrinoidsandspongesdominatingthecommunity.Thereefplatformisdistinctfromtheseothertwozonesinitshigherenergyandhardersubstrates,withrelativelyhighgravelcontent.Faunasonthereefplatformshowhighdiversity,withanabundanceofascidiansandoctocorals.

How are species related to physical factors?Byvariousmechanisms,thephysicalfactorsidentifiedinthisstudycanbeassociatedwiththetypesoforganismspresent.Theseafloorpropertiesareclearlyassociatedwiththehabitatmodesoftheorganisms.Theareaswithasandyseafloor,suchastheshelfandbasinareas,aredominatedbymobiledepositfeedersandinfauna,sincethoseorganismsrequireasoftseafloorinwhichtheycanburrowandforageforfood(Jumars1993).Gravellyareas,suchasonthereefandbryomolreefareas,containhighproportionsofsuspensionfeeders,whichattachtothestronganchorpointsavailableintheseenvironments.

Seabeddisturbanceisameasureofthestabilityoftheseabedenvironment.Inareaswithalowfrequencyandmagnitudeofdisturbance,competitionbetweenorganisms

“Themodernreefenvironmentisdividedintothreedistinctzones,eachwithamoderatetohighseabeddisturbance”

Mapping marine diversity �

issue 84 Dec 2006

isgreater,whichtendstosuppressdiversity(Connell1978).Therelativelylowseabeddisturbanceoftheshelfandbasinenvironments(lowtomoderate)inthisstudyismostlikelyassociatedwiththeloweroverallspeciesdiversityinthoseenvironments.Inareasofveryhighfrequencyandmagnitudeofdisturbance,diversityisalsosuppressedduetothehighvariabilityoftheenvironment,whichreducesreproductivesuccessandtheabilityofthecommunitytomatureorberecolonisedbeforethenextdisturbanceevent(Connell1978).

Anareaofveryhighdisturbanceinthisstudyoccursonthetalusslopeadjacenttothemainpatchreef.Thespeciesdiversityontheslope,whichischaracterisedbyactivesedimentation,issubstantiallylowerthanatthesurroundingreefsites,wheresedimentinputismuchlower.Thiscomparisonsuggeststhatareasoflowersedimentinputandlowerdisturbance(suchasonthereefs)supportalargervarietyoffaunascomparedtohighlyvariableareas(suchasthetalusslope)wherespeciesdiversityissuppressed.Somedegreeofdisturbancealsoreflectscurrentflows;thesecanbringinnutrientsandotherfoodsources,whichareparticularlyimportantforsuspensionfeeders.

Insummary,thisstudyrevealsanassociationbetweenthesedimentcompositionandthetypesofmacroorganismspresent,andparticularlytheirhabitatmodes.Mobileandinfaunalspeciesaremoreprevalentonsoftersubstrates,whilesuspensionfeedersdominateareaswithhighergravelcontentandhardersubstrates.Theseabeddisturbancemayreflectthesupplyoffoodviacurrentstosuspensionfeedersinareasofmoderatedisturbance,whilelowdisturbanceleadstoreduceddiversity,whichcouldbeduetohigherlevelsofcompetition.Thehighseabeddisturbanceonthesandysubstrateofthetalusslopeisalsoassociatedwithalowdiversityofmobileorganisms,reflectingthestresstoorganismsinhigh-energyenvironmentswhereanchorpointsarenotavailable(e.g.Connell1978).Thewaterdepthprimarilyreflectschangesinlightintensity,temperature,oxygen,salinityandenergy(Murray1991),andisassociatedwiththedistinctcommunitiesthatoccurbetweentheshelfandbasinenvironmentsinthisstudy.

Applying physical relationships for marine planningThebiophysicalrelationshipsestablishedfromthisstudycanbeusedtopredictthediversityanddistributionofmarinebenthicorganismsacrossthebroaderregionoftheNorthernPlanningArea.Thefourphysicalparametersthatshowthestrongestrelationshiptotheseabedbiota(mudcontent,gravelcontent,seabeddisturbanceandwaterdepth)werecombinedusingexistingdatasetsacrossthebroaderregionwithanunsupervisedclassification.Fiveclassesareformedfromthisclassification,andtheirdistributioncanbeusedtointerpretthedistributionofpotentialseabedhabitats(figure4­).Weobtainfurtherinformationabouthabitatvariabilitybyoverlayingthegeomorphicfeatures.Throughtheproductionofhabitatmapssuchasthese,marinemanagerscantakeamorerigorousapproachintheselectionofmarinereserves.

ConclusionsDeterminingrepresentativeareaswithintheNorthernPlanningAreaforprotectionaspartofanetworkofMPAsisnotcurrentlypossiblebasedonthesparselydistributedbiologicaldatacurrentlyavailableforthisregion.Physicaldatasets,however,canprovideinformationaboutthevariations

“Thisstudydemonstratesthatselectedphysicaldatasetsarewellcorrelatedtothedistributionoftheseabedbiotainthisregion”

Mapping marine diversity �

issue 84 Dec 2006

inthephysicalenvironment,andhencethevariationsintheseabedhabitats.Thisstudydemonstratesthatselectedphysicaldatasetsarewellcorrelatedtothedistributionoftheseabedbiotainthisregion.Bycombiningthesebroadlydistributedphysicaldatasets,wecanproducemapsthatshowthedistributionofdistinctmarinehabitatsintheregionandprovidemarinemanagerswithinformationaboutthepredicteddistributionofseabedcommunities.

ThisinformationwillprovideamorerigorousbasisfortheselectionofrepresentativeareasforprotectionwithinanetworkofMPAs.AtGeoscienceAustralia,continuingresearchensuresthathabitatmapswillbebasedonrigorouslytestedparameters.Thoseparameterswillneedtobegoodpredictorsofseabedbiotafortheregionsthattheyareappliedto.CurrentresearchisfocusingonanumberofregionsinAustralia’smarinejurisdiction,includingthenorthwestandsouthwestregions.

For more information

phone AlixPoston+612624­99023

email alix.post@ga.gov.au

References

ConnellJH.1978.Diversityintropicalrainforestsandcoralreefs.Science199:1302–1310.HarrisPT.Inpress.ApplicationsofgeophysicalinformationtothedesignofarepresentativesystemofmarineprotectedareasinsoutheasternAustralia.In:ToddBJ&GreeneG(eds),MarineBenthicHabitatMapping,GeologicalAssociationofCanadaandGEOHAB.HeapA,HarrisP,PasslowV,WassenbergT,HughesM,SbaffiL,MathewsE,FellowsM,FountainL,Porter-SmithR,DaniellJ,BuchananC&RobertsonL.2006.SourcesandsinksofterrigenoussedimentsintheSouthernGulfofCarpentaria.GeoscienceAustraliaRecord2006/11.JumarsPA.1993.ConceptsinBiologicalOceanography:Aninterdisciplinaryprimer.OxfordUniversityPress,NewYork.KostylevVE,ToddBJ,FaderGBJ,CourtneyRC,CameronGDM&PickrillRA.2001.BenthichabitatmappingontheScotianShelfbasedonmultibeambathymetry,surficialgeologyandseafloorphotographs.MarineEcologyProgressSeries219:121–137.MurrayJW.1991.EcologyandPalaeoecologyofBenthicForaminifera.LongmanScientificandTechnical,Harlow,UK,39.

RameyPA&SnelgrovePVR.2003.SpatialpatternsinsedimentarymacrofaunalcommunitiesonthesouthcoastofNewfoundlandinrelationtosurfaceoceanographyandsedimentcharacteristics.MarineEcologyProgressSeries262:215–227.PostAL,WassenbergTJ&PasslowV.2006.Physicalsurrogatesformacrofaunaldistributionsandabundanceinatropicalgulf.MarineandFreshwaterResearch57:4­69–4­83.SchropeM.2005.Deepseaspecial:Theundiscoveredoceans.NewScientist2525:38–4­3.ThouzeauG,RobertG&UgarteR.1991.FaunalassemblagesofbenthicmegainvertebratesinhabitingseascallopgroundsfromeasternGeorgesBank,inrelationtoenvironmentalfactors.MarineEcologyProgressSeries74­:61–82.ZachariasMA&RoffJC.2000.Ahierarchicalecologicalapproachtoconservingmarinebiodiversity.ConservationBiology14­:1327–1334­.