Benthic Assemblages of the Anton Dohrn Seamount

33 Pages·2015·15.32 MB·English

RESEARCHARTICLE
Benthic Assemblages of the Anton Dohrn
Seamount (NE Atlantic): Defining Deep-Sea
Biotopes to Support Habitat Mapping and
Management Efforts with a Focus on
Vulnerable Marine Ecosystems
JaimeS.Davies1*,HeatherA.Stewart2,BhavaniE.Narayanaswamy3,ColinJacobs4¤,
JohnSpicer1,NeilGolding5,KerryL.Howell1
1 MarineBiologyandEcologyResearchCentre,PlymouthUniversity,Plymouth,PL48AA,UnitedKingdom,
2 BritishGeologicalSurvey,MurchisonHouse,WestMainsRoad,Edinburgh,EH93LA,UnitedKingdom,
3 ScottishAssociationforMarineScience,ScottishMarineInstitute,Oban,Argyll,PA371QA,United
Kingdom,4 NationalOceanographyCentre—Southampton,EuropeanWay,Southampton,Hampshire,
SO143ZH,UnitedKingdom,5 JointNatureConservationCommittee,MonkstoneHouse,CityRoad,
Peterborough,PE11JY,UnitedKingdom
¤ Currentaddress:GardlineGeosciencesLtd,1HewettPark,HewettRoad,GreatYarmouth,NR310NN,
OPENACCESS UnitedKingdom
* [email protected]
Citation:DaviesJS,StewartHA,Narayanaswamy
BE,JacobsC,SpicerJ,GoldingN,etal.(2015)
BenthicAssemblagesoftheAntonDohrnSeamount
(NEAtlantic):DefiningDeep-SeaBiotopestoSupport Abstract
HabitatMappingandManagementEffortswitha
FocusonVulnerableMarineEcosystems.PLoSONE In2009theNWandSEflanksofAntonDohrnSeamountweresurveyedusingmultibeam
10(5):e0124815.doi:10.1371/journal.pone.0124815
echosounderandvideoground-truthingtocharacterisemegabenthicbiologicalassem-
AcademicEditor:AndrewDavies,Bangor blages(biotopes)andassessthosewhichclearlyadheretothedefinitionofVulnerableMa-
University,UNITEDKINGDOM
rineEcosystems,foruseinhabitatmapping.Acombinationofmultivariateanalysisofstill
Received:December16,2013 imageryandvideoground-truthingdefined13comprehensivedescriptionsofbiotopesthat
Accepted:March20,2015 functionasmappingunitsinanappliedcontext.ThedatarevealsthattheNWandSEsides
ofAntonDohrnSeamount(ADS)aretopographicallycomplexandharbourdiversebiologi-
Published:May18,2015
calassemblages,someofwhichagreewithcurrentdefinitionsof‘listed’habitatsofconser-
Copyright:©2015Daviesetal.Thisisanopen
vationconcern.TenofthesebiotopescouldeasilybeconsideredVulnerableMarine
accessarticledistributedunderthetermsofthe
CreativeCommonsAttributionLicense,whichpermits Ecosystems;threecoralgardens,fourcold-watercoralreefs,twoxenophyophorecommu-
unrestricteduse,distribution,andreproductioninany nitiesandonespongedominatedcommunity,withremainingbiotopesrequiringmorede-
medium,providedtheoriginalauthorandsourceare
tailedassessment.Coralgardenswereonlyfoundonpositivegeomorphicfeatures,namely
credited.
parasiticconesandradialridges,foundbothsidesoftheseamountoveradepthof1311–
Funding:Thisworkreceivedfundingfromthe
1740m.Twocold-watercoralreefs(equivalenttosummitreef)weremappedontheNW
MASTSpoolinginitiative,(TheMarineAlliancefor
ScienceandTechnologyforScotland),specifically sideoftheseamount;Lopheliapertusareefassociatedwiththeclifftopmoundsatadepth
fromtheDeepSeaForumandtheirsupportis of747–791mandSolenosmiliavariabilisreefonaradialridgeatadepthof1318-1351m.
gratefullyacknowledged.MASTSisfundedbythe
Xenophyophorecommunitiesweremappedfrombothsidesoftheseamountatadepthof
ScottishFundingCouncil,(grantreferenceHR09011)
1099–1770mandwereeitherassociatedwithgeomorphicfeaturesorwereincloseproxim-
andcontributinginstitutions.Theworkwasfundedby
theJointNatureConservationCommittee;theyhad ity(<100m)tothem.Thespongedominatedcommunitywasfoundonthesteepescarp-
someinputinthestudydesigntomeettheirsurvey menteithersideoftheseamountoveratadepthof854-1345m.Multivariatediversity
objectives.
PLOSONE|DOI:10.1371/journal.pone.0124815 May18,2015 1/33
BenthicAssemblagesoftheAntonDohrnSeamount
CompetingInterests:CJisanemployeeofGardline revealedthexenophyophorebiotopestobetheleastdiverse,andahardsubstratumbio-
GeosciencesLtd.Therearenopatentsorproductsin topecharacterisedbyserpulidsandthesessileholothurian,Psolussquamatus,asthe
developmentormarketedproductstodeclare.This
mostdiverse.
doesnotaltertheauthors'adherencetoallthePLOS
ONEpoliciesonsharingdataandmaterials.
Introduction
Increasingpressureonthemarinerealmhasresultedintheneedforgreaterunderstanding
andbetterspatialmanagementofourmarineenvironment.Thisishappeningatbothnational
andgloballevelsandinparticularthereisarealimpetusfortheestablishmentofnetworksof
MarineProtectedAreas(MPAs)drivenbyglobal,Europeanandnational(withintheUK)ini-
tiatives[1–3].OneofthecriteriabywhichMPAsareselectedincludestheprotectionofhabi-
tatsandspeciesthathavebeenidentifiedasrare,sensitive,functionallyimportant,threatened
and/ordeclining[4].
Anumberofhabitatsarelistedunderthesevariousinitiativesincluding,butnotlimitedto,
cold-watercoralreefs,coralgardens,spongedominatedcommunities,andcommunitiesthat
arecomposedofepifaunathatprovideastructuralhabitat(e.g.xenophyophoresandseapens)
forotherassociatedspecies.ThesehabitatsarelistedintheAnnexoftheInternationalGuide-
linesfortheManagementofDeep-SeaFisheriesintheHighSeas[5]asexamplesofspecies
groups,communities,habitatsandfeaturesthatoftendisplaycharacteristicsconsistentwith
VulnerableMarineEcosystems(VMEs).OSPARhashighlightedanumberofdeep-seahabitats
as‘threatenedordeclining’,andtheseincludeamongstothers,seamounts,Lopheliapertusa
reefsandcoralgardens;whilecold-watercoralreefs,coralgardensandspongedominatedcom-
munitiesaredefinedasAnnexIlisted‘reef’habitatundertheHabitatDirective[1].
Seamountsarelargetopographicalfeaturesoftencharacterisedbycomplexhydrodynamic
regimes[6].Theyexertaninfluenceoveroceancurrentsbyinterruptingtheflowofwater,this
cancausetidestobeamplifiedcreatingfastcurrentsandproducingeddies[7,8].Theseelevat-
edcurrentshaveafunctionalrolebyincreasinglocalfoodsupply,erosionanddepositionof
sediment,andinsomecasesexposinghardsubstratumforfaunalattachmenttherebyincreas-
inglarvalsupplyandspeciesrecruitment;thusmakingseamountsdiversebiologicalfeatures
[9].
Seamountssupportarichfauna,andareconsideredbiodiversityhotspotswithhighlevels
ofendemism[6,9,10,11,12,13,14]thusprovidingasignificantroleinspeciesdispersalby
actingassteppingstones[9,10,11].Theincreasedspeciesrichness(ascomparedtothesur-
roundingseafloor)issuggestedtobearesultofhighcarboninputstothesesystemsandthe
availabilityofhabitats[13].Inrecentyearsseamountecologyandhydrographyhavereceived
considerableresearchinterestinanattempttounderstandseamountecosystems[13,15,16,
17,18].
Todate,asmallnumberofMPAshavebeenestablishedintheNEAtlanticdeep-sea/High
Seasusingoneormoreoftheselegalmechanisms.ExistingMPAshavebeendesignatedbased
ontheknownoccurrenceofLopheliapertusae.g.NEAFC/EUfisheriesclosuresandUKGov-
ernmentproposalsforSitesofCommunityImportanceonHattonandRockallBanks[19–21],
orareseamountse.g.NEAFCfisheriesclosuresontheMidAtlanticRidge(MAR)[22].The
NEAFCfisheriesclosuresontheMARfallwithinaproposedOSPARMPA[23]whichencom-
passesalargeareanorthandsouthoftheCharlie-GibbsFractureZone.Todatetherehave
beennoclosuresmadeforotherlistedhabitatseventhoughseamountsarelistedunderAnnex
VofOSPARasfeaturesthatmaysupportVMEs[5].Seamountsprovideimportanthabitats
PLOSONE|DOI:10.1371/journal.pone.0124815 May18,2015 2/33
BenthicAssemblagesoftheAntonDohrnSeamount
andharbourmanylistedspecies(e.g.Lopheliapertusa),andassuchneedprotectionthrough
theinclusionintoMPAs.AntonDohrnSeamountisjustoneofseveralseamountsfoundinthe
NEAtlanticthatisknowntosupportVMEs.
OneoftheprincipaldifficultiesindesignatingMPAsfortheprotectionoflisteddeep-sea
habitatsisalackofdetaileddistributiondata.Mappingthesehabitatsisvitalforpolicymakers
andgovernmentsiftheiroffshoreareasaretobemanagedproperly.Habitatmappingcanbe
undertakenatdifferentspatialscales,rangingfromindividualorganismsuptoecosystemsand
landscapes[24].Theuseoflargetopographicalfeaturessuchasseamountsandbanks(mega-
habitatlandscapefeatures,sensuGreeneetal.[25])atscalesofkilometrestotensofkilometres
hasbeenused[26],andprovenusefulforbroadscalemappingoverlargeareas.Whilstbroad
scalemappingmayadequatelyrepresentsomehabitats,othersarenotdistributedatthesame
spatialscaleandthusrequireadifferentapproach.Toadequatelyrepresentthebiologyitis
necessarytounderstandthedistributionofhabitatsatadataacquisitionlevel,orfine-scale,
whichcanberelatedtotypicallymoregeneralised,broadscalemapsthatcoverawider
geographicarea.
Anecessarypreludetomappingisidentifyinganddescribingthebiologicalassemblages
(biotopes).Biologicalassemblagesor‘biotopes’areusedasmappingunits,wheretheyrepre-
sentdistinctbiologicalassemblagesassociatedwithcertainenvironmentalfactorssuchassub-
stratumanddepth[27].Existingdeep-seabiotopesaregenerallydefinedonthebasicofthe
epibenthicmegafauna,whicharemostsensitivetoanthropogenicdisturbance,thuschangesin
thiscommunitycanbeaneasilymonitoredindictorforsmallcompartments[28].Additionally
megafaunaareknowntoincreasestructuralcomplexityandprovideshelterforotherorgan-
isms,thusincreasinglocaldiversity[29].Toallowcomparabilitybetweenmapsfromdifferent
areas/regions,essentialfortheimplementationandmanagementofMPAs,itisimportantto
useconsistentmappingunitsandtohaveadequatedescriptionsforthesehabitatssothatthese
termscanbeusedacrossgeographicregions[25,30].Inthedeepseatherehavebeenfewat-
temptstoproducedescriptionsofbenthicassemblagesforuseinmapping[31–37].Whilst
somebenthicassemblagesarebroadlyrecognisedthroughthescientificliterature,e.g.cold-
watercoralreefsandostur(spongecommunities),othershavebeendescribedthroughthepo-
liticalprocess(e.g.coralgardens[38]).Fewlisteddeep-seahabitatsaresupportedbyscientifi-
callyrobustdescriptionsofcommunitycompositionsuchthatcoherentmappingunitscanbe
described,andtherelationshipbetweenlistedhabitatsand‘moreeasilymapped’geomorpho-
logicalfeaturesremainsunknown.
Relationshipsbetweenbiologicalassemblagesandgeomorphologicalfeaturesatamesohabi-
tatscale(tensofmetrestoakilometre;sensuGreeneetal.[25])havebeenreported,e.g.cold-
watercoralreefsassociatedwithmoundfeatures[34,39–42].Oncetherelationshipbetweenbi-
ologicalassemblagesandgeomorphologyisunderstood,itmaythenbepossibletorelatebio-
logicalassemblagestobroad-scalegeomorphologicalfeatureswhichareinherentlymoreeasily
mappedandcanbeusedasasurrogatetopredictthedistributionofbenthichabitats.Thisap-
proachisparticularlyimportantinthedeepseaandforhabitatsofconservationconcernsuch
aslistedhabitats.
Theaimsofthispaperareto1)identifythedeep-seamegabenthicassemblagesofAnton
DohrnSeamountthatcanbeusedasclassificationunitsinhabitatmappingefforts,2)identify
biotopesofconservationinterestunderinternational/nationalpolicyand3)todescribethedis-
tributionofthesebiotopesinrelationtothegeomorphologyoftheseamountsystem.
PLOSONE|DOI:10.1371/journal.pone.0124815 May18,2015 3/33
BenthicAssemblagesoftheAntonDohrnSeamount
Methods
Ethicsstatement
Nospecificpermissionswererequiredfortheselocations(57.28°N10.82°W—57.61°N
11.22°W)andthefieldstudiesdidnotinvolvecollectionofendangeredorprotectedspecies.
Studyarea
AntonDohrnSeamountisaroughlycircularseamountcentredat57°27’N,11°5’W,located
tothewestofScotlandintheRockallTroughbetweentheHebridesShelfandRockallBank
(Fig1).Thissteepsidedseamountisapproximately45kmindiameterwitharelativelyflat
summitatadepthof~600mbelowsealevelrisingfromadepthofover2000m.Anumberof
pinnaclesarelocatedonthesummitoftheseamount,thehighestofwhichreach530mbelow
sealevel.AntonDohrnSeamountisalsoencircledbyawell-developedmoatfeaturewhich
deepensfromthenorth-west(~2195m)tothesouth-east(~2300m).Thebulkoftheseamount
probablycomprisesbasalticlavas[43–45]withasouth-eastthickeningwedgeofsedimentson
thetopoftheseamountidentifiedonBritishGeologicalSurvey2Dseismicreflectiondata.
ThehydrographicactivitywithintheRockallTroughiscomplexandhasbeenstudiedfor
manyyears.EasternNorthAtlanticWaterflowsalongthecontinentalslopeandentersthe
southernpartoftheRockallTroughandcirculatesinananti-cyclonicdirectionandexitsthe
troughtothenorth-west[46].Theslopecurrentcontinuestotransportwarm,salinewater
alongtheshelfnorthwardsacrosstheWyville-ThomsonRidgeintotheFaroe-ShetlandChan-
nel[47].Thenorth-westflankofAntonDohrnSeamountmaybeinfluencedbyArcticwaters
thatperiodicallyoverflowtheWyville-ThomsonRidgebutitisunlikelythattheSEsideofthe
seamountisinfluencedbythiscurrent[48].
Samplingmethods
In2009,thenorth-westandsouth-eastflanksofAntonDohrnSeamountweresurveyedusing
multibeamechosounderandvideoground-truthingtoidentifyVMEs(Fig1)overafourweek
period(July2009)usingthecommercialresearchvesselMVFranklin.Highresolutionacoustic
datawerecollectedusingahullmountedKongsbergEM710multibeamechosoundersystem
capableofoperatinginwaterdepthsuptoaround2000m.Swathwidthwasbetween1.0–1.5
kmandtheoperatingfrequencyrangeforthesystemwas70–100kHz.Datawereprocessed
on-boardandgriddedataresolutionof15mtoallowdetailedinterpretationofmeso-scale
geomorphologicalfeatures.
Inordertocharacterisethemegabenthicassemblagesoftheseamount,transectswereselect-
edtocapturetherangeofhabitats/terrainsoneithersideoftheseamount,withaparticular
focusontopographicalfeaturessuchasmounds.Thiswasachievedbyusingtheprocessed
multibeambathymetryandbackscatterintensitydatatoselecttransectsthatrepresenteddiffer-
entdepths,interpretedgeomorphologyandseabedsubstratum(inferredfrombackscatterin-
tensitydata).Wheretimepermittedandadequatenumberoftargetswerepresent(e.g.depth
range,geomorphologyandseabedsubstratum)replicatetransectswereundertakenwithinand
betweenthetwostudyareas.Theorientationofthetransectsreflectthetopography,orienta-
tionofthegeomorphologicalfeature,tomaximisethedepthrangesampled,orwasdetermined
bytheprevalentoceaniccurrentsandweatherconditionsthatimpactsafedeploymentandre-
coveryofequipment.
Videoandimagedatawerecollectedfromatotaloftentransects(fourlocatedinthenorth-
westandsixinthesouth-east;Fig2.)usingadrop-framecamerasystemtowed1–3mabove
theseabedatavesselspeedofapproximately0.5kn.Astargetedfeaturedvariedinlength,so
PLOSONE|DOI:10.1371/journal.pone.0124815 May18,2015 4/33
BenthicAssemblagesoftheAntonDohrnSeamount
Fig1.ThestudyareawestofScotland,UK.SurveyareasontheNWandSEsidesofAntonDohrnSeamountaremarked.Bathymetriccontoursare
providedbyGEBCO,the200mdepthcontour(dashedline)markstheapproximatepositionofthecontinentalshelfbreak.
doi:10.1371/journal.pone.0124815.g001
didthelengthoftransectstoallowcompletesamplingofthefeatures.Thesystemcompriseda
5megapixelKongsbergOE14-208digitalstillscameraandanintegratedDTS6000digital
videotelemetrysystem.Thedrop-frameisalsofittedwithsensorstorecorddepth,altitude
abovetheseabedandtemperature,andanultra-shortbaseline(USBL)beacon(calibratedbe-
foreuse),whichisfullyintegratedwiththevessel’sdigitalgeographicpositioningsystem
(DGPS),tocollectaccuratepositionaldataforthecameraframe[49].FollowingtheMESH
guidelinesfordatacollection[50],a2–5minutecamerastabilisationperiodwasundertakenat
thebeginningofeachtransecttoensurethecamerawasmovingataconstantspeed.Video
footagewasrecordedalongtheentiretransect,andatapproximatelyoneminuteintervalsthe
drop-framewaslandedandastillsimagetaken(samplingunit)hereinafterreferredtoasa
‘sample’image.Acalibrationgrid,ofknowndimensions,wasattachedtotheframepriortoini-
tiationofsamplingtodetermineimageareawhentheframewasontheseabed(0.156m2),1m
(0.539m2),2m(2.11m2)and3m(3.65m2)offtheseabedandrelatedtosampleimageto
allowabundance/percentageareacoveroffaunatobeexpressed.Transectlengthvariedbe-
tween0.5kmand3.3kmoveradepthrangeof747–1887m.Variationinlengthwasdueto
transectstargetingspecificfeatureswhichvariedinsize,impactofoceaniccurrentsandadverse
weatherduringoperations.
Biologicalanalysis
Quantitativeanalysisofimagedata. Thesampleimageswerequantitativelyanalysed
usingthecalibrationgridasameasureofarea.Identificationofspeciesfromimagesisoften
PLOSONE|DOI:10.1371/journal.pone.0124815 May18,2015 5/33
BenthicAssemblagesoftheAntonDohrnSeamount
Fig2.CameratransectssampledfromtheNW(top)andSE(bottom)surveyareasofAntonDohrnSeamountoverlaidonmultibeambathymetry.
Selectedbathymetriccontoursareshownasdashedlineswithlabelledwaterdepthsinmetresbelowsealevel.
doi:10.1371/journal.pone.0124815.g002
difficult;howeverobservedorganismswereidentifiedasdistinctmorphospecies(morpho-
types).Allvisibleorganisms>1cm(atwidestpoint)wereidentifiedasdistinctmorphospecies
PLOSONE|DOI:10.1371/journal.pone.0124815 May18,2015 6/33
BenthicAssemblagesoftheAntonDohrnSeamount
andassignedanOperationalTaxonomicUnit(OTU)number[51].OTUswereidentifiedto
thelowestpossibletaxonomiclevel.Allindividualswerecountedexceptinthecaseofencrust-
ing,colonialandloboseforms,wherepercentagecoveroftheorganismwasrecorded.Highly
mobilespeciessuchasfishwereremovedpriortodataanalysis.Imagedatawereexpressedas
eitherindividuals/1m2orpercentcover/1m2.InaccordancewithJNCCguidelines,datawere
archivedwiththeMEDINDataArchiveCentreshttp://www.oceannet.org/.
Communityanalysis. Standardmultivariatecommunityanalysistechniques[52]were
usedtoidentifyfaunallydistinctbenthicassemblageswithinthestudyarea.Standardisationof
countandcovermatriceswasundertakentoplacethemonacommonscaletoallowasingle
combinedanalysis(R.Clarkepers.comm;[34]).Eachmatrixwassquareroottransformed,di-
videdthroughitselfandmultipliedtoputonacommonscaleof0.005–0.75(count(cid:1)200and
(cid:1)
cover 100).Clusteranalysiswithgroup-averagedlinkagewasperformedusingaBray-Curtis
similaritymatrixderivedfromtransformed,combinedspeciescountandpercentcoverdata.
TheSIMPROFroutinewasusedtoidentifysignificantclustersusingasignificancelevelof
p<0.01andtheSIMPERroutineusedtoidentifythosespeciesthatcharacterisedsignificant
clusters.Characterisingspeciesweredefinedasthosespecieswithahighsim/SDratio[53],
andcontributed>5%tothatcluster’ssimilarity.
Characterisingmappingunits(biotopes)
Thereisadiscrepancybetweenthefaunalassemblagesidentifiedusingcommunityanalysis
methodsandwhatisrequiredfromapracticallyapplicablemappingunitusedinproducing
necessarygeneralisedmapsofvariationinthebiologicalcompositionoftheseabed.Tocharac-
terisepracticalmappingunitsthatcanbemappedatascaleappropriatetothatoftheacoustic
data,thoseclustersidentifiedasfaunallydistinctusingstandardclusteranalysistechniques
wereassessedagainstasecondsetofcriteriatodeterminetheiruseasmappingunits.Only
thoseclusterswhichmetthesecriteriawerefurtheranalysedintermsoftheirfaunalcomposi-
tionanddiversity.Tofunctionasamappingunitassemblagesmust,1)occuratascalerelevant
totheresolutionoftheacousticdata,andthescaleofexisting,widelyacceptedbenthiccommu-
nitiessuchascold-watercoralreefs(10mscale),and2)beeasilyidentifiedfromvideodata.
Biotopesweredefinedintermsoftheircharacterisingspecies,asdeterminedbySIMPER
analysis,togetherwiththerangeofenvironmentalconditionsoverwhichtheyoccurredinthis
study.AOne-wayAnalysisofSimilarity(ANOSIM)wasundertakenonanormalised,Euclide-
andistancematrixofenvironmentdata(depthandtemperature)totestifenvironmentalcon-
ditionsweredifferentbetweenbiotopes.
Toassesswhetherbiotopescouldbeconsideredofconservationconcern,identifiedbiotopes
werecomparedwithcurrentdefinitionsofOSPARandtheECHabitatsDirectivelistedhabi-
tats.InidentifyingthosethatwouldbeconsideredasVMEsweusedtheAnnextotheguide-
linesoftheFAO[5]andcurrentOSPARdefinitions.ThislimitstheidentificationofVMEsto
thosebiotopesthatcontaintheexamplespeciesorcommunitiesidentifiedinthatAnnex.We
havenotconsideredbiotopesaccordingtothewidercriterialistedinthefulldocument.
Diversityindices. Megafaunaldiversityintermsofspeciesrichnessanddominancewere
measuredtocomplimentthecharacterisationofbiotopes,andallowamorecompletedescrip-
tionofassemblages.Simpson’sReciprocalIndex[1/D]wasmeasuredusingtheDIVERSErou-
tineinPrimerv6[52]togiveSimpson’sdiversityindex(λ)andthereciprocalformtakenby1/
D.Simpson’sReciprocalindexwaschosenasameasureofdominanceasitislesssensitiveto
samplesize[54].Countandcoverdataweremeasuredseparatelyforeachsampleimageand
thenaveragedtogiveasingleSimpsonmeasureperimage,andexpressedasthemeanSimp-
son’sReciprocalIndexperbiotope.
PLOSONE|DOI:10.1371/journal.pone.0124815 May18,2015 7/33
BenthicAssemblagesoftheAntonDohrnSeamount
Speciesrichnesswasmeasuredusingthreemethods:1)meanspeciesrichnessperbiotope,
2)rarefaction,3)incidence-basedspeciesrichnessestimators(ICE,Chao2,Jackknife1and2,
andbootstrap)usingEstimateS8.3.Rarefactioncurvesestimateexpectedspeciesrichness
(MaoTauSobs)forasub-sampleofthepooledtotalspeciesrichness,basedonthespeciesactu-
allydiscovered(asopposedtoestimatorsthatestimatespeciesrichnessincludingspeciesnot
sampled)[55]andallowinterpolationatlowersamplesize,thusovercomingsamplingbias
andvaryingsamplesize[56].Jackknifeisanon-parametricspeciesrichnessestimatorwhich
removessubsetsofthedataandre-calculatestheestimatorusingthereducedsamples,andisa
goodtechniqueforreducingbias[55,57].TherearetwoJacknifeestimators:FirstorderJack-
knifeisafunctionofthenumberofrarespeciesinacommunity,whereitcalculatesthenum-
berofspeciesthatoccurinonlyonesample;andsecondorderJackknifewhichadditionally
calculatesthenumberofspeciesthatoccuronlyintwosamplesinacommunity[58].ICE(in-
cidence-basedestimator)estimatesthesamplecoverage,bytheproportionofassemblagerich-
nessrepresentedbythesetofreplicatedincidencesamples.Thatis,theproportionofall
frequenciesofinfrequentspecies(foundin10orfewersamples)whicharenotuniquespecies.
Chao2isanasymptoteestimatorofminimumrichness[55].Bootstrapisaresampling
procedure.
Asinglediversityindexisoftennotsufficienttoallowadequatecomparisonsbetweenas-
semblages[59]thusmultipleindiceswereusedtocomparediversityofbiotopes.ANOSIM
tests(Primerv6[52])onEuclideandistanceresemblancematriceswereundertakentotestfor
significantdifferencesindiversitybetweenbiotopes(Ho:nosignificantdifferenceindiversity
betweenbiotope).Asuiteofnormaliseddiversitymeasures[Simpson’sReciprocalIndex,ex-
pectedspeciesrichness(Sobs)andthefiveincidence-basedestimators]wereusedtogiveaho-
listicviewofthediversitymeasure.
Distributionofbiotopesinrelationtomeso-scalegeomorphology. Geomorphological
classeswereinterpretedfromthemultibeamechosounderdata(Table1).Videotransectswerere-
viewedandvisuallyclassified(guidedbythesampleimageanalysisclusteroutput)usingthenewly
definedbiotopes,andchangesofbiotopetypewithinatransectmappedusingArcGIS9.3.Biotope
mappedvideodatawereoverlaidonaninterpretedgeomorphologypolygonlayerinArcGISand
usedtoqualitativelydescribethedistributionofbiotopesinrelationtomeso-scalegeomorphology,
particularlyfocusingonthosebiotopesidentifiedasVMEs.Abioticdatawerealsoextractedfrom
themappeddatatodefinetheenvironmentalrangeofthedistributionofeachbiotope.
Results
Biologicaldata
Over14hoursofvideoand2745stillsimageswerecollected,ofwhich744imagesweredesig-
natedsampleimages.Forty-threesampleimageswereomittedfromtheanalysisduetopoor
Table1. Meso-scalegeomorphologicalfeaturesidentifiedfromthesummitandflankofAntonDohrn
Seamount.
Summit Flank
Cliff-topmounds Flute
Cliffedge Escarpment
Parasiticcone
Radialridge
Landslide/Rockfall
Furrow/moat
doi:10.1371/journal.pone.0124815.t001
PLOSONE|DOI:10.1371/journal.pone.0124815 May18,2015 8/33
BenthicAssemblagesoftheAntonDohrnSeamount
quality,and41samplesthatcapturedabruptchangesinsubstratumwereaddedtotheanalysis.
Duetothetaxonomiccomplexityoftheimages,timeconstraintsdidnotallowforanalysisof
allsampleimages,thuseverythirdsample(approx.3minintervals)wasquantitativelyanalysed
(320images).OntheNWsurveyareatransectswerecollectedoveradepthrangeof747–1770
mtotalling7.1kmlineofvideowhilstatotalof6.4kmlineofvideowerecollectedoveradepth
rangeof956–1889mfromtheSEarea.Atotalof253morphospecieswereidentifiedand
catalogued.
Communityanalysis. Thirty-threeclusters(Fig3A)wereidentifiedusingtheSIMPROF
routine(p<0.01),outlierclusters(a-f)andthosewhichcontainedlessthaneightimages(l,m,
n,x,y,z,ab)werediscarded.Uponexaminationofcluster“h”(whichcontained>8images)it
wasapparentthattheseimagescapturedamicrohabitatwithinthebiotopeofcluster“k”and
wasthereforenottreatedasacoherentclusterandwerenotinvestigatedfurther.Cluster“ad”
wassubjectivelydividedonthebasisofsubstratum(bedrockanddeadcoralframework)inline
withcurrenthabitatclassificationschemes[SeeFig3A,cluster(ad)].Sixclusters[SeeFig3A,
clusterslabelledas(o-t)]werecombinedatahigherlevelofsimilarity,aswereclustersu,vand
w.Reasonsforcombiningclusterso-tandu,vandwbymovingupanodeintheclusteranaly-
sisoutputareasfollows:uponfurtherexaminationoftheunderlyingimagedataitwasclear
thatthesamplesfromthesixclustersalloccurredonthesteepescarpmentfeature.Thenature
oftheterrainaffectedhowclosethedrop-framecameracouldgettotheseabed,thusmaking
consistentsamplingdifficult.Thiswasreflectedinthesamples,withvaryingsamplesizescap-
turingfaunaatdifferentscales.Theseclusterswerenotdeemedtoberobustandwerecom-
binedatalowerlevelofsimilarity.Giventheproblemwiththechangingsizeoffieldofviewit
couldbearguedthatthesedatashouldbeomitted.However,thiswouldhaveresultedinnore-
presentationatallofthecommunitiesoccurringonthistypeofterrainandseabedfeature,
which,giventheaimsofthestudyandthescarcityofdatafromseamounts,seemedtheless
favourableoption.Thus,thedatawereretainedbuttreatedwithadegreeofcaution.Clusters
werere-labelledwiththeupdatedchanges(Fig3B)andtheseupdatedlettersusedthroughout
theremainderofthemanuscript.
TheSIMPERroutinewasrepeatedtoincorporatethemodifiedclustersasdescribedabove,
andresults,alongwithenvironmentaldata,canbefoundinS1Table;fullSIMPERresultscan
befoundintheS1Appendix.
Characterisingmappingunits(biotopes)
Intotal13megabenthicassemblageswereidentifiedfromtheclusteranalysisandrelatedto
availableenvironmentaldatatodescribedistinctandusefulmappingunits[biotopes(seeFig4,
Table2)].Codeswereallocatedforthoseclustersthatdescribedbiotopes;g(Oph.Cer),i(Lop.
Mad),j(Syr.Car),k(Syr.Oph),o(Por.Pso),p(Ser.Pso),t(Sol.Oph),u(Lop.Oph),w(Sol.Car),
x(Sol.Por),y(Lep.Par),z(Ker.Sol),aa(Gor.Zoa).TheOne-wayANOSIMtestperformedon
theenvironmentaldata(depthandtemperature)associatedwitheachbiotoperevealedasignif-
icantdifferenceinenvironmentalconditionsbetweenbiotopes(GlobalR=0.652;p<0.01).
Fortythreepairwisetestsweresignificant.
VulnerableMarineEcosystems
Cold-watercoralreefs. Fourbiotopesweredefinedthatcouldbeconsideredascold-water
coralreef,twoarecharacteristicofsummitreefandtheothertwoofframeworkstructures.
Livebiogeniccoralreef(Lop.Mad)wascharacterisedbythereefbuildingcoralsLophelia
pertusa(livecoloniesandframework)andMadreporaoculata,thepencilurchinCidaris
cidaris,anemones(Actiniariasp.),decapods(Decapodasp.5)andthesquatlobsterMunida
PLOSONE|DOI:10.1371/journal.pone.0124815 May18,2015 9/33
BenthicAssemblagesoftheAntonDohrnSeamount
Fig3.Dendrogramofhierarchicalclusteranalysisofspeciesdata,clustersidentifiedusingtheSIMPROFroutine(p<0.01).Dendrogram(A)shows
theSIMPROFclusterresultspriortosplittingandconsolidationofclustersand(B)showsre-labelledclustersaftersplittingandconsolidation.Thoseclusters
thatwerecombinedorsplitfromFig.3aarelabelledinred.SIMPROFclustersarecollapsedforeaseofinterpretationandarerepresentedbygreendashed
lines.GreylinesrepresentSIMPROFidentifyingwithnosignificantinternalstructure.
doi:10.1371/journal.pone.0124815.g003
PLOSONE|DOI:10.1371/journal.pone.0124815 May18,2015 10/33