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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.
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References
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