BENTHICHABITATSOF THEDELAWAREBAY BenthicHabitatsoftheDelawareBay BenthicHabitatsofDelawareBay MarkG.Anderson,JosephA.M.Smith,andBartholomewD.Wilson INTRODUCTION ThissectiondescribesandmapsthemajorphysicalhabitatsoftheDelawareBayseafloor.Weused informationonbenthicorganisms,theirdistributionandtheirrelationshipstophysicalfeatures,to delimitadistinctsetofenvironmentsrepresentingthevarietyofbenthichabitatsintheBay.As individualspeciesareadaptedtovariationsindepth,sedimentsize,seabedtopographyandsalinity,we examinedthesefactorsinrelationshiptotheorganismcompositionandclassifiedthemintobasictypes toillustratethediversityofconditionsexistingontheseafloor.Wehopethatthisbenthichabitatmapof theDelawareBay,basedonpreviouslycollecteddata,willprovideabetterunderstandingofthe abundanceanddistributionofseafloorhabitattypes. Benthicorganismsarethosethatinhabittheseafloor;fromtheGreekwordbenthos,meaning“depths ofthesea.”Basedonajustasmallsample(246samples),theseafloorhabitatsoftheDelawareBay containover300speciesin8phylaincluding: 106speciesofarthropods(crabs,lobsters,shrimp,barnacles) 75speciesofmollusks(clams,scallops,squid,limpets,seaslugs,snails) 130speciesofannelids(seaworms) 8speciesofechinoderms(seastars,seaurchins,seacucumbers,sanddollars) 5speciesofcnidarians(corals,anemones,jellyfish) 4speciesofchordates(seasquirts) 1speciesofporiferans(sponges) 6speciesofnemerteans(ribbonworms) Thedistributionsandlifehistoriesofbenthicorganismsaretiedtotheirphysicalenvironment.Filter feederstendtodominateonshallowsandybottomswhiledepositfeeders,maydominateinfine grainedmud.Itisthesedistinctphysicalhabitatsthatweidentified,characterized,andmapped. Thischapterrepresentsaninitialefforttodefineandmapmarinebenthichabitatsusinginformationon organismdistributionscombinedwithinterpolateddataonbathymetry,sedimentgrainsize,and seafloortopography.Thegoalwastoproduceabaywidemapofbroadlydefined,butdistinctwith respecttotheorganismgroupsfoundwithinthem. ThisworkisbuildsonthemethodsdevelopedintheNatureConservancy’sNorthwestAtlanticMarine assessment,(Greenetal.2010)particularlythosedescribedinchapter3BenthicHabitats. Pleasenotethatcriticalstepsofaccuracyassessment,crossvalidationusingindependentdatasets, comparisonswithdemersalfishhabitat,andfinalexpertpeerreviewareongoing BenthicHabitatsoftheDelawareBay DefinitionofTargetHabitats ThegoalofthisworkwastoidentifyandmapthemajorbenthichabitattypesintheDelawareBay.We definedabenthichabitatasagroupoforganismsrepeatedlyfoundtogetherwithinaspecific environmentalsetting.Forexample,siltflatsindeepwatertypifiedbyaspecificsuiteofamphipods, clams,whelksandsnailsmightbeonehabitat,whilesandflatsinshallowwatermightbeanother, providingitsupportsadifferentsetoforganisms.Conservationofthesehabitatsisnecessarytoprotect thefulldiversityofspeciesthatinhabittheseafloor,andtomaintaintheecosystemfunctionsofbenthic communities. METHODS TodesignaconservationplanforbenthicdiversityintheDelawareBayitisessentialtohavesome understandingoftheextentandlocationofvariousbenthichabitats(e.g.amap).Fortunately,the challengeofmappingseafloorhabitatshasproducedanextensivebodyofresearch(seeKostylevetal. 2001;Greenetal.2005;Auster2006;WorldWildlifeFund2006;ToddandGreene2008).Inaddition, comprehensiveseafloorclassificationschemeshavebeenproposedbymanyauthors(seeDethier1992; Brown1993,EuropeanEnvironmentalAgency1999;Greeneetal.1999;Alleeetal.2000;Brown2002; Conneretal2004;Daviesetal.2004;Greeneetal.2005;Maddenetal.2009;Valentineetal.2005; Kutcher2006;andseereviewsinNationalEstuarineResearchReserveSystem2000andLundand Wilbur2007).DuringdevelopmentofthebenthicmapfortheNatureConservancy’sNorthwestAtlantic MarineAssessment(Andersonetal.2010inGreeneetal.2010),wereviewedtheliteratureonseafloor classification,andexaminedthevarietyofapproachesalreadyutilizedinordertodevelopthe methodologyusedhere. Manyoftheexistingschemesbasetheirclassificationsonphysicalfactorssuchasbathymetry,sediment grainsize,sedimenttexture,salinity,bottomtemperature,andtopographicfeatures.Thisislogicalas thereisampleevidencethatbenthicdistributionpatternsareassociatedwithmanyofthesevariables. Forexample,temperatureiscorrelatedwiththecommunitycompositionofbenthicmacroinvertebrates (TherouxandWigley1998);substratetypeiscorrelatedwithcommunitycompositionandabundanceof boththeinvertebratesanddemersalfish(Austeretal.2001;Stevensonetal.2004);habitatcomplexity iscorrelatedwithspeciescomposition,diversity,andrichness(EtterandGrassle1992;Kostylevetal. 2001;SerranoandPreciado2007,reviewsinLevinetal.2001);anddepthiscorrelatedwithabundance, richness,andcommunitycomposition(Stevensonetal.2004). Theapproachusedherebuildsonexistingschemesbothexplicitlyandimplicitly,andresultscanbe readilycomparedtothem.However,thegoalofthisassessmentwastoproduceamapofbroadly definedbenthichabitatsinBayusingreadilyavailableinformation,andwearenotproposinganew classificationsystem. BiologicalFactors:BenthicOrganisms Themapofbenthichabitatspresentedhereisbaseddirectlyonthedistributionandabundanceof benthicorganismsinDelawareBay,andtheknowledgeofthesespeciesandtheirdistributionscomes BenthicHabitatsoftheDelawareBay largelyfromseafloorsamplesdescribedbelow.Intheanalysisofthisdata,groupsofspecieswithshared distributionpatternswereidentified,thenthresholdsinthephysicalfactorswereidentifiedthat correlatedwiththosepatterns.Specifically,threebasicstepswerefollowed:1)quantitativeanalysisof thegrabsamplestoidentifydistinctandreoccurringassemblagesofbenthicorganisms,2)recursive partitioningtorelatethespeciesassemblagestophysicalfactors(bathymetry,sedimenttypes,and seabedtopographicforms),and3)mappingthehabitatsbasedonthestatisticalrelationshipsbetween theorganismgroupsandthedistributionofthephysicalfactors.Althoughorganismdistributionswere usedtoidentifymeaningfulthresholdsandcutoffsinthephysicalvariables,thefinalhabitatmapsare composedsolelyofcombinationsofenduringphysicalfactorsandarethuscloselyrelatedtothemaps andclassificationschemesproposedbyothers. Thisstudywasmadepossiblebyaccessto234samplesofabundanceandbiomassdatacollectedbythe DelawareEstuaryBenthicInventoryPartnershipfortheDelawareEstuaryandEPARegion2andRegion 3.DataSamplingoccurredduringSummer2008(forsamplingprotocolseeEPA'sNCAorPDE'sDEBI QAPP)TheDEBIeffortwasmultidisciplinaryandmanyfederal,stateandregionalpartnerscontributed withdesign,sampling,sampleanalysisanddataanalysisproducts.ThePartnershipfortheDelaware Estuary(PDE),aNationalEstuaryProgram,wasthecoordinatingentityandgrantee,workingclosely withEPARegion3andtheEPAAtlanticEcologyDivision.Asreportsandadditionaldataanalysis productsareat:http://www.delawareestuary.org/science_projects_baybottom.asp. TwelvemoresampleswereprovidedbytheNationalMarineFisheriesService’s(NMFS)Northeast FisheriesScienceCenter(NEFSC).TheNEFSCconductedaquantitativesurveyofmacrobenthic invertebratefaunafromthemid1950stotheearly1990sandafewofthesesamplesincludedDelaware Bay.Organismscollectedineachsamplewereidentifiedtospecies,genus,orfamily.Athorough discussionoftheNEFSCsamplingmethodology,geartypes,history,andananalysisofthebenthic dataset,includingthedistributionandecologyoftheorganisms,canbefoundinthepublicationsof WigleyandTheroux(1981and1998). ClassificationMethods Classificationanalysisbeganwiththeentire234seafloorsamplesobtainedfromtheDEBIPandthe12 samplesfromNEFSC.ThesewerecombinedintoasamplebyRspeciestableindicatingtheabundance(by count)ofeachspecieswithineachsample.Wherepossibletheanalysiswasdoneatthespecieslevelbut insomecases,whenanorganismwasabundantinmanysamplesbutonlyidentifiedtogenus,thegenus wastreatedasaspecies.Speciesthatonlyoccurredinonesamplewereremovedfromthedataset beforeanalyzingthedataaswasinformationonplants,eggmasses,andorganicdebris. Sampleswithsimilarspeciescompositionandabundanceweregroupedtogetherusinghierarchical clusteranalysis(PCORD,McCuneandGrace2002).Thistechniquestartswithpairwisecontrastsofevery samplecombinationthenaggregatesthepairsmostsimilarinspeciescompositionintoacluster.Next,it repeatsthepairwisecontrasts,treatingtheclustersasiftheyweresinglesamples,andjoinsthenext mostsimilarsampletotheexistingclusters.Theprocessisrepeateduntilallsamplesareassignedtoone ofthemanyclusters.Forouranalysis,theSorensonsimilarityindexandtheflexiblebetalinkage techniquewithBetasetat25wasusedasthebasisformeasuringsimilarity(McCuneandGrace2002). BenthicHabitatsoftheDelawareBay Aftergroupingthesamples,indicatorspeciesanalysiswasusedtoidentifythosespeciesthatwere faithfulandexclusivetoeachorganismgroup(DufreneandLegrande1997).Lastly,MonteCarlotestsof significancewererunforeachspeciesrelativetotheorganismgroupstoidentifydiagnosticspeciesfor eachgroupusingthecriterionofapvaluelessthanorequalto0.10(90%probability).Thenumberof setsofclusters(testing10to40)wasdeterminedbyseeingwhichamountgavethelowestaveragep value. PhysicalFactors:Bathymetry,SubstrateandSeabedForms Tounderstandhowthebenthicinvertebratecommunitydistributionsrelatedtothedistributionof physicalfactors,aspatiallycomprehensivedatalayerforeachfactorofinterestwasdeveloped.Four aspectsofseafloorstructurewereused:bathymetry,sedimentgrainsize,topographicforms,and salinity.Thesefactorswerechosenbecausetheyarecorrelatedwiththedistributionandabundanceof benthicorganisms.Dataoneachphysicalfactorwerecompiledfromseparatesourcesandthe techniquesusedtocreateacomprehensivemaparediscussedbelow. Bathymetry WebasedourbathymetrydatasetonapubliclyavailabledigitalelevationmodelfortheDelawareBay (estuarinebathymetry.noaa.gov).Inordertouseallofthebiologicalsamplesinouranalyses,we extendedthebathymetrycoverageupriverapproximately20kilometers(Figure1).Todothis,weused