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CHAPTERW
TheSeaasaBiologicalEnvironment
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Intheforegoingchaptersanaccounthasbeengivenofthechemical andphysicalaspeetsoftheelementsthattogetherconstitutetheinorganic marineenvironment-namely,(1)theseawateritself,and(2)theocean floors.Thechemicalconstituentsandthephysicalpropertiesofthe seawater,togetherwiththeirdistribution,concentrations,andcyclic changes,themovementofthewater,andthenatureoftheoceanfloors aredecisivefactorsinthehwtoryandfateofaperplexingarrayofliving things.Hereinareheldmanysecreteofracialdevelopment,andherein mustbesoughttheunderstandingofthedelicatelybalancedmaintenance oflifeandofthepotentialitiesoffuturedevelopment. Marineorganismsaretobeconsideredapartoftheseaasitexists today. Justasseawaterincludesthevarioussalts,bothconservative andnonconservative(biologicallychanged),soalsoitincludesthe multitudeoforganismswhichareboundtotheseafortheirexistence andwhich,byorigin,areapartoftheseabothraciallyandindividually. Theorganisms,likethesalts,aresubjecttothenaturallawsofthesea andare apartoftheperpetualcycleofinorganicandorganicsubstances soimportantinmanyaspectsofoceanography.Thechangesthatare apparentinconcentrationrepresentonlypatternsthatareinherentin thephasesofthecycleorthatresultfromothercauses,suchMcurrents andprocessesofmixing. Theaquaticenvironmentoffersthegreatestintimacybetweenitself andtheorganismswhichitbathesbothoverthebodysurfacearidwithin openorpartiallyclosedcavitiesas,forexample,theinternalsystemsof coelenterat+echinoderms,andtunicates.Becauseofthestabilityof thephysicalcharacteristicsoftheseawaterandofthecompositionand concentrationofthedissolvedsaltstheorganisms,ingeneral,havenot developedhighlyspecializedintegumentsandregulatorysystemsto protectthemselvesagainstsuddenandintenseenvironmentalchanges, sshavemostlandanimals.Itfollowsthatsmallchangesintheaquatic mediumarepromptlybroughttoplayuponitapopulation.Itshould beborneinmind,also,thattheorganismsthemselves,beingapartofthe dynamicenvironment,modifyparticularlyitschemicalcharacterby withdrawingoraddingsubstancesassociatedwiththeactivitiesoflife. 267
268THESEAASABIOLOGICALENVIRONMENT
Insubsequentchaptersweshalldiscusstherelationofsomeof themeasurableenvironmentalfactorstosuchphenomenaasdistribution, propagation,survival,andspecialadaptations,butfirstsomefactsof generalapplicationmustbeconsidered. PhysicalandChemicalCharacteristicsoftheMarineEnvironment Waterisessentialtothemaintenanceofalllife.Itconstitutes
80percentormorebyweightofactiveprotoplasm.Itisthemost
e$icientofallsolventsandcarriesinsolutionthenecessarygases,oxygen andcarbondioxide,aswellasthemineralsubstancesnecessarytothe growthofplantsandanimals,anditisitselfoneoftheessenfialraw materialsinthemanufactureoffoodsbyplants. Organismslivingintheterrestrialenvironmenthavedevisedmeans, suchasimperviousinteguments,toconservewater,andthelandplants haverootsandspecialvascularsystemsfortransportofwatertoall growingparts.Inthemarineenvironmentthereisjreedomfromdessica- kion,exceptathigh-tidelevels,andthereforenoKlghlyspecializedmeans areprovidedforconservationofwaterorforitstransportinplants. Alsoofbiologicalimportancearethehighheatcapacityofwaterand itshighlatentheatofevaporation,bothofwhichobviatethedangerthat mightresultfromrapidchangeoftemperatureintheenvironmental medium.Owingtothehighdegreeoftransparencyofwateritispossible fortheseatosustainplantlifethroughoutarelativelydeeplayer,and inanimalsthedevelopmentoforgansofvisionandoforientationhas progressedtoamarkeddegree. Seawaterisabq$eredsolution;thatis,changesfromacidtoalkaline condition,orviceversa,areresisted(p.195).Thispropertyisofvital importancetothe-marineorganisms,mainlyfortworeasons:(1)an abundantsupplyofcarboncanbeavailableintheformofcarbondioxide fortheuseofplantsinthesynthesisofcarbohydrateswithoutdk- turbancetotheanimallifethatmaybesensitivetosmallchangesin pH,and(2)intheslightlyalkalinehabitatthemanyorganismsthat constructshellsofcalciumcarbonate(orothercalciumsalts)cancarry onthisfunctionmuchmoreefficientlythaninaneutralsolution. Thesupportofferedtothebodiesofmarineorganismsbythespecific gravityofthesurroundingmediumobviatestheneedofspecialsupporting skeletalstructureinmanyforms.Strikhgexamplesofthesearethe jellyfishes,unarmoredmolluscs,unarmoreddinoflagellates,andeven thelargemarinemammalswiththeirheavyskeletons,whichcouldnot surviveintheirpresentbulkystateexceptinanaquatichabitat.The hardshellsofcrabs,clams,snails,andsoon,doubtlessserveassupport, especiallyinsomeburrowingandintertidalforms,butthesehardparts maybelookeduponalsoasprotectiveandasaframeworkforattach- mentofmusclesusedindigging,creeping,orswimming.
THESEAASAB1OLC3GICALENVIRONMENT269
SEAWATERANDTHEBODY
FLUIDS.Seawaterisamostappropriate
environmentforlivingcells,sinceitcontainsallofthechemicalelements essentialtothegrowthandmaintenanceofplantandanimalprotoplasm. Ithaebeenshownthatseawaterisasolutionofalargenumberofsalts, anditisimportantheretoconsiderhowitisrelatedasanexternalfluid mediumtothe'finternalmedium'' - namely,thebodyfluids(blood,* coelomicfluid,andsoon)oftheorganisms.Theratiosofthemajor saltstoeachother,andusuallytheirtotalconcentrationalso,arestrik- inglysimilarinseawaterandinthebodyfluidsofmarineinvertebrates. Thesimilarityofcompositionisnotconfinedtomarineanimals,however, butisalsoinevidenceinmodifiedforminbothterrestrialandfresh- wateranimals,includingthelowerandhighervertebrates,asisshown intable55,whichisfromdatacompiledbyPantin(1931)andexpanded by
Dakin(1935).
OSMOTICRELATIONSHIPS.Itiswellknownthatwhensolutionsof differentosmoticpressureareseparatedbyasemipermeablemembrane thatallowsthepassageofwaterbutnotofthesolutes,thereisamove- mentofthewaterthroughthemembraneintothemoreconcentrated solution.Thecellmembranesoforganismsarejustsuchsemipermeable membranesthroughwhichamovementoffluidsoccursinwardorout- ward,dependinguponwhethertheosmoticpressureoftheexternal medhmisless(hypokmic)orgreater(hypertonic)thantheinternal medium.Theinternalandexternalmediaareisotonicwhentheyareof equalosmoticpressure. Theosmoticpressureofasolutioncanbecomputedfromthefree~ing- pointdepression(p.67).Thiscomputationispossiblebecausethe saltsthatincreasetheosmoticpressureofasolutionalsodepressits freezingpoint.Thefreezing-pointdepressionbelowO"Chasbeendesig- natedbyA@f(p.67),butwillherebeabbreviatedtoA.Seawaterhav- ingasahityof35.oo'/00freezesat-1.91°,owingtodepressionbythe substancesinsolution.Inotherwords,thevalueforAis1.91°.Simi- larly,weobtainaAof0.56forhumanbloodwithafreezingpointof -0.56°C. OnthebasisofAvalues,theosmoticrelationsofthebodyfluids ofmarineandfresh-wateranimalstotheirexternalenvironmental mediumarecomparedintable56,fromdatacompiledbyDakin(1935), towhosereviewthereaderisdirectedformuchgreaterdetniland historicaltreatment. Fromthefewexamplesinthetableitisevidentthatthebodyfluids ofmarineinvertebratesareisotonicornearlysowiththeirfluidenviron- ment,whereasinthefresh-waterformathebodyfluidsarehypertonic tothediluteexternalmedium.Forthisreasonthemarineenviron- mentinitsosmoticrelationsfailstoexactofitsinhabitantsasgreatan expenditureofenergyinmaintainingtheproperconcentrationofbody
270THESG4ASABIOLOGICALENVIRONMENT
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THESEAASABIOLOGICALENVIRONMENT271
fluidsmdamthefresh-waterenvironment.Theexaetimeohardsm wherebythefresh-wateranimalsareindependentoftheexternalmedium andareabletomaintainahonzoiiowwticcondition(thatis,steadyvalue forA)inthepresenceofthehypotonicwaterisnotknown(seeAforthe eelAn@laanguillainfreshandsaltwater,table56).Theirexistence undertheseconditions,however,requiresaconstantexpenditureof energyineliminating,throughthekidneysandotherexcretoryorgans, theexcesswatertakeninbyosmosis.Marineinvertebratesarepoihil- osmotic(Achangingwiththat'oftheexternalmedium)onlywithin rathernarrowlimits(Dakin,1935);hence,they,too,musthavesome regul&tingmechanism.Exceptinestuarineconditions,however,the rangeofsalinityinmostpartsoftheseaisperhapswithinthelimitsof poikilosmoticityoftheinvertebrateslivingthere.Forexample,the lugworm,Areniicotamarina,inHelgolandwaterswithaA1.72hasan internalmediumAl.7,butintheBalticSeawithawaterofAO.77the samespecieshasaAvalueof0.75fortheinternalmedium. Itshouldbementionedherethattheteleost(bony)fishesinmarine watersaredefinitelyhypotonicand,therefore,inordertokeeptheir bodyfluidsdowntotherequiredosmoticpressureforthespecies,they secretechloridethroughthe"chloridecells"ofthegills(Keys,1933). Thisfunctionisaregulationtowardalowosmoticpressureoftheblood, asopposedtoregulationtowardahighoneasperformedbythekidneys ofanimalsinfresh-waterenvironments.Thatthisgroupofaquatic animalshasachievedamarkeddegreeofindependenceoftheosmotic pressureoftheexternalmediumisevidencedespeciallybysuchforms asthesalmonandeel,bothofwhich,thoughpracticallyhomoiosmotic, spendtheirlivespartlyinhypotonicandpartlyinhypertonicenviron- ments. Theelasmobranchs-namely,thesharksandrays - areisotonic withseawater,butinthesethehighosmoticpressureofthebloodis duenotonlytothepresenceofsuchsaltsasoccurinseawater,butalso tohighureacontent.Forfurtherdiscussionofsalinityt-isanenviron- mentalfactor,seealsop.839.
OtherCharacteristicsoftheEnvironment
Inadditiontothechemicalandphysicalpropertiesofseawater, certainotherbiologicallyimportantcharacteristicsareinherentinthe marineenvironmentasawhole.Theseresultfromthemagnitudeof theoceanitself,itsgreatdepth,anditsexpanse. Inconsideringtheoceaninitsentiretyasanenvironment,weare atfirstimpressedbythewiderangesoflivingconditions,thesalinities varyingfromthoseofdiluteestuarianwaterstoconcentrationsof370/00 ormoreintheopensea,temperaturesfrom30*Ctofreezingpoint, lightintensitiesfrombrilliantsunlightatthesurfacetoabsoluteand perpetusddarknessinthedeeperlayers,andpressuresfromasingle
THESEAASABIOLOGICALENVIRONMENT
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THESEAASABIOLOGICALENVIRONMENT273
atmosphereatthesurfacetoabout1000atmospheresinthegreatest oceanicdeeps. Impressiveastheserangesmaybe,neverthelessveryuniformcondi- tionsdoprevailoverextensiveareasofthe.environment,andmany organismsmay,byreasonofthemonotonyoftheseextensiveareas,be verydelicatelyattunedtotheprevailingunvaryingconditions.Hence, itfollowsthatfaunaIareascharacterizedbyspecificformscanberecog- nized.Ontheotherhand,awide'rangeofconditionsmaybeencountered inmorerestrictedareas,especiallyincozstalregions.Theseconditions maybeduetothephysiographiccharacterofthecoastline,depthto bottom,topographyandnatureofthebottom,inflowoflanddrainage, meteorologicalconditions,andsoforth.SpeciaIlyadaptedandtolerant formsoccurhereinprofusion,for,aswillbeshowninlaterchapters,the shallowdepthsandvaryingconditionsarefrequentlyfavorableto abundantproductionofprimaryfood. Itmustnotbeoverlookedthatthegradientsofsalinity,light,and temperaturethatexistintheseaarefavorabletoanumberofsensitive animalsthatpossesstheability,throughswimmingorotherwise,to adjustthemselvestooptimumconditions. DEPTHANDLIGHT.Inherentintheverticalrangeordepthofthe open-seahabitatareanumberofimportantfeaturesoffar-reaching biologicaleffect.Ofprimeimportanceistherelativelygreatvertical rangeoftheeuphoticzoneavailableforproductionoffloatingmicroscopic plants.Butthegradientoflight,bothastoquantityandquality, resultingfromdepthofwateralsoallowsadjustmentofmanyanimals totheoptimumconditionwithrespecttothisfactorand,indeed,is associatedwithdiurnalmigrationsofmanyformstolighterordarker situations. PRESSURE.Pressureinitselfdoesnotexcludelifefromtheabyssal regionsofthesea,forwaterisbutlittlecompressedandequilibrium existsbetweentheinnerandouterpressureaffectingthebodytissues. However,pressuremaylimittheverticalrangeofmotileforms,although someeurybathicanimalsapparentlyarenotseriouslyaffectedandare knowntomakedailyverticalwanderingsofupto400m,corresponding topressurevariationsupto40atmospheres.Harpoonedwhalesare saidto"sound"toadepthof800m,andthespermwhalesmustdescend normallytogreatdepths,sincethelargesquidsuponwhichtheyfeed inhabitverydeepwater.
WATERMOVEMENTS,Theseamustbeviewedasanenvironment
thatforthemostpartisinconstantmotionwithbothregularandirregu- larpatternaofflow.Theprincipalbiologicalbenefitsderivedfromthe circulationare(1)oxygenationofsubsurfacewater,(2)dhpersalof wastesresultingfromprocessesofmetabolism,(3)dispersalofplant nutrientsandothervariableelementsessentialtoplantandanimal
274THESEAASABIOLOGICALENVIRONMENT
growth,and(4)d~persalofspores,eggs,larvae,andalsomanyadults. Onthewhole,thecirculationofwaterisofdirectbenefit,yetinstances maybenotedwheresomeadverseconditionsresulteitherasincidental oraspermanentfeatures.Incidentaldisturbancesmaybedueto unseasonableshiftsintheregularcurrentsystem,suchasgiverisetothe appearanceof"ElNifio"offthewestcoastofSouthAmerica(p.
704).Inthisinstance,warmwateroftheEquatorialCountercurrent
iscarriedsouthwardalongthecoaetsofEcuadorandPeru,whichare normallybathedbycoldcurrents.Theresultisawholesaledestruction ofanimallifealongthecoast,includingmanyguanobirdsthatdepend upontheseaforfood.Permanentorsemipermanentfeaturesofcurrent systemsthattakearegulartolloflifearefoundwherethemovingwater carriestheinhabitantsintoareasoflessfavorablelivingconditions. Forexample,GulfStreaminhabitantsultimatelyperishastheyare sweptnorthwardintoregionswherethetemperatureofthewateris loweredbyadmixtureofcoldwaterorbycoolinginhigherlatitudes. Larvaeofneriticformsarefrequentlydispersedtooffshoreorother locationsuninhabitabletotheadultanimals.Surfacecurrentssometimes strewtheshoreswithdefunctbodiesofnormallyoceanicoroffshore formssuchasthecoelenterateVelte2aorthepelagicsnailJanthina.
EXTENTOFTHEMARINEENVIRONMENT.Thatpartoftheearth
whichiscapableofsustaininglife,bothplantandanimal,isknownas theMosphere.Thebiosphereissubdividedintothreeprincipaldivisions orhabitatsknownasMocyctes.Thesearetheterrestrial,themarine, andthefresh-waterbiocycles.Eachhasitscharacteristictypesof ecologicalfeaturesandassociationsofplantsandanimals.Afew animalspeciesmayattimesmigratefreelyfromonetoanother,asis witnessedespeciallybythesalmonortheeel. Theoceanscoversome71percentoftheearth'ssurface.Thus, theareaoftheoceansisabouttwoandonehalftimestheareaofthe land,but,whenconsideringthespaceinwhichlifemightconceivably exist,accounthastobetakenoftherelativeverticalrangeprovided bythetwomainenvironments,theterrestrialandthemarine.Onthis basisitisestimated(Hesse,Allee,andSchmidt,1937)thatthemarine environmentactuallyprovidesaboutthreehundredtimestheinhabitable spaceprovidedbytheterrestrialandthefresh-waterbiocyclestogether; for,whereastheterrestrialenvironmentprovidesspaceonlyinashallow zonemainlyattheimmediatesurfaceandtoadepthofafewfeetatthe most,themarinehabitatprovideslivablespaceforatleastsomeformof lifefromthesurfaceeventotheabyssaldepthofseveralmiles.The fresh-waterbiocycleconstitutesonlyasmallfractionoftheothertwo. Theaerialportionoftheglobeisnotproperlyconsideredaseparate biocycle,sinceentrancesintoitbybirds,insects,andsoforthmaybe consideredmainlyastemporaryjourneys.
THESEAASABOIQGKJAL
OwingtotheWieultiesattendanton
marineblocycleistheIeaetknownofall.
ENVIRONMENT275
thestudyoftheoceans,the
ClassificationoftheMarineEnvironment
Inordertofacilitateastudyofthemarineenvironmentandits irihabltante,theformermay}econvenientlydividedbroadlyintoprimary andsecondarybioticdkisionsbaseduponphysical-chemicalattributesor uponthenatureoftheblots.Theboundariesbetweenthesebiotic
Fig.67.Themaindivisionsofthemarineenvironment.
diviions,whicharediagrammaticallyshowninfig.67,areinsome instanceswelldefined,butmorefrequentlythereisagooddealofover- lapping.Thus,althoughtheprimarydivisionsaredefinitelysetoff fromeachotheronphysicalbases,andthetypicalsubdivisionsofthese habitatscanbeclearlyrecognizedbothblotieallyandabioticdly,yet therearenowell-definedboundariesbetweenthem.
Thetwoprimarydivisionsoftheseaarethe
bertthicandthepek@. Theformerincludesalloftheoceanfloor,whilethelatterincludesthe wholemassofwater. THEBENTHICBIOTICENVIRONMENTANDITSSUBDIVISIONS.This divhionincludesallofthebottomtei?minfromthewave-washedshore lineatflood-tideleveltothegreatestdeeps.Itsupportsacharacteristic typeoflifethatnotonlylivesuponbutcontributestoandmarkedly modifiesthecharacterofthebottom.Ekman(1935)discussesthe boundariesoftheverticalzonesfromazoogeographicstandpoint,and wefollowmainlytheschemeemployedinhistext.
276THESEAASABIOLOGICALENVIRONMENT
Thebenthicdivisionmaybesubdividedintotwomainsystems - namely,thelittoralandthedeep-seas@ems.Thedividinglinebetween thesehasbeensetatadepthofabout200monthearbitrarysupposition thatthisrepresentstheapproximatedepthofwaterattheouteredge ofthecontinentalshelf(p,20),and,roughly,alsothedepthseparating thelightedfromthedarkportionofthesea.Thelittoralsystemis subcWdedintotheeulittoralandthewblittoratzones.Thedeep-sea systemisdividedintoanupper(archibenthic)andalower(abyssal- benthic)zone.Thelimitsofthebenthicsubdivisionsarehardtodefine, andarevariouslyplacedbydifferentauthorsbecauseuniformboundaries thatwillfitallrequirementscannotbedrawn.Forgeneralbiologiad studies,thedifferentboundariesmustbebasedonthepeculiaritiesofthe endemicplantandanimaldistributionandshouldfollowtheregionof mostdistinctfaunalandfloralchange.Thebioticzonesthusdelineated willbecharacterizedbyamoreorlessclearlydefinedrangeofexternal ecologicalfactorswhichhavegivencharactertothepopulation. Theeulittoralzoneextendsfromthehigh-tideleveltoadepthof about40to60m.Thelowerborderissetroughlyatthelowestlimit atwhichthemoreabundantattachedplantscangrow.Thesublittoral zoneextendsfromthisleveltoadepthofabout200m,ortheedgeofthe continentalshelf.Thedividinglinebetweenthesesubdivisionsvaries greatlybetweenextremes,sinceitisdeterminedbypenetrationoflight sufficientforphotosynthesis.Itwillberelativelyshallowinthehigher latitudesanddeepinthelowerlatitudes.Intheupperpartofthe eulittoralzonearelativelywell-definedtidalorintertidalzonethatis boundedbythehigh-andlow-waterextremesofthetideisrecognized. ~Someauthorsconfinetheeulittoralzonetothisnarrowsectionand considerthesublittoraltobeginatthelow-tidelevel(cf.Gislen,1930). Theverticalrangeoftheintertidalzone,thoughratherwelldefinedfor anygivenarea,variesgreatlyincWferentsectionsoftheworld,foritis determinedbythetidalrange(seechapterXIV).Intheupperreachesof theBayofFundythezonemayhaveaverticalrangeofover15m, whileintheGulfofMexicoitislessthan0.7m,andinareaslikethe MediterraneanalongthesouthwestcoastofItalytherangeisyetsmaller, only10to30cm.Onexposedcoastssubjectedtodirectoceanwaves andswellstheupperrangeissomewhatextendedtoincludearather well-definedsupratidalsprayzonewithasparsepopulationofespecially resistantformsamongwhichafewanimals,suchastheisopodLig~da, appeartobeintheprocessofbecomingterrestrialinhabit.Many speciesofanimalsarefoundonlyinthetidalzoneandmaybelimited verticallyinmaximumdistributioneventocertainlevelswithinthe zone-forexample,LigpdaandthegaetropodsLdtorinascutalata,L. planaxis,Acrnaeadigitalis,andothersfoundatMontereyBayonly abovethe0.76-mtidallevel(Hewatt,1937).Thus,inthetidalzone
THESEAASABIOLOGICALENVIRONMENT277
inwhichtherangeinexternalfactorsisgreatestwefindamorerestricted verticalrangeofspecificanimals.thanisobviousanywhereelseinthe benthicregionofthesea.Manymotileanimals,forexamplecrustaceans andfishes,moveregularlyintotheintertidalzonetofeedduringhigh tide,andthesmaIlpelagicfishknownasgrunionmigrateintothezone duringcertainhighspringtidestodeposittheireggsinthesand. Theeulittoralzonegivesrisetomanybiotopes,foritisgreatlyvaried astotypeofsubstratum - forexample,rocky,sandy,ormuddy - and alsoastocharacterofshorelineanddegreeofexposure.Theoverlying watermaybeslightlyorgreatlyreducedinsalinity.Thesevariations aredirect,decisivefeaturescontrollingthetypeandabundanceof sessilelittoralforms(cf.Shelfordetal,1935).Theplentifulprimaryfood inthiszoneisderivedfrombothpelagicandattachedplants. AttemptstoestabliihsuchzonesasFucuszone,Laminarianzone, andsoon,basedonthedepthsatwhichtheseplantsarecharacteristically attached,hasthedisadvantagethattheplantsareveryfrequently absentalongvtwtstretchesofthecoast,owingtounfavorablesubstratum orotherecologicalfactors;nevertheless,suchclassificationmaybeof usefullocalapplication. Thoughtheboundarybetweenthesublittoralandthedeep-sea systemsissetatadepthof200m,Ekman'scompilationsbasedonthe faunaindicatethatinmostregionstheboundarymaybelocatedbetween
200and400m.Lightandtemperatureareimportantfactors,andin
highlatitudesthesefactorsoperatetogethertoshifttheboundaryinto shallowerwater. Theupperdivisionofthedeep-seasystemiscalledthearchibnthic,. awordintroducedbyAlexanderAgassi~,butthetermisunfortunatein thatitimpliesthebeginningofthebenthosfromthisregion.Thezone isalsocalledthecoru%w%ldeep-seazone,butthisgivesrisetogreater confusion,sincetheterm"continentalfauna"sometimesusedmust inoludealsothelittoralfaunaunlessspecificallycalledcontinenW-&lope ordeep-seafauna.Theurchibenthiczoneextendsfromthesublittoralto adepthbetween800and1100m. Theaby=ssal-benthiczonecomprisesallofthedeep-seabenthicsystem belowthearchibenthiczone.Itisaregionofrelativelyuniformcondi- tions.Temperaturesareuniformlylow,from5°to-1°C,andsolar lightiswanting.Therearenosezsons,andhencetheseasonalbiological phenomenaassociatedwiththelittoralzonearesuppressed.Stagnant conditionsdonotprevailintheopenocean,however,forthereisample circulationtosupplywell-aeratedwaterresultingfromdeepvertimd movementsinthehighlatitudes(p.138).Noplantsareproduced,and theextenttowhichautotrophlcbacteriaplayapartinthemanufacture offoodisnotknown.Theanimalsarecarnivorous,feedingmainly uponorganicdetrituswhichinitsinitialorganicstatemusthaveorigi-
278THESEAASABIOLOGICALENVIRONMENT
natedintheplantsofthesurfacewaters.Theabyssalzone,though notsharplymarkedoffatiteupperlimitsfromthearchibenthiczone, hasitsowncharacteristicpopulation,aswillbebroughtoutinafollowing chapter. TheberAhkenvironmentfromshoreseawardtoabyssaldepthsis covered,toagreaterorlessdegree,bysedimentarydepositsthatmaybe classifiedasterrigenousdeposits,organicorpelagicoozes,andredclay. AdetaileddiscussionofthedepositswillbefoundinchapterXX,and thenatureofthedistributionisshowninfig.253.Asfarasthebiology ofbenthicanimalsisconcerned,themostimportantfeaturesofthese oozesaretheirphysicalconsistenciesandtheamountofdigestibleorganic materialtheycontain.Mostdeep-seabenthicformsaredetritus eatersandmainlydependent,therefore,upontherainofpelagicorganisms thatfallstothebottom.Theproductionofpelagicfoodusuallydecreases markedlywithincreasingdistancefromthecoast,andtheamountreach- ingthebottominareasofverydeepwaterisfurtherreducedbyits disintegrationwhilesinking.Hence,thelittoralmudsaremostrichin food,andtheredclayatgreatdepthsandfarfromshoreisthepoorest. Thisdifferenceisreflectedinthenumberofanimalsactuallycollected fromdifferentareas(&f.p.806). THEPELAGICENVIRONMENTANDITSSUBDIVISIONS.Thepelagic divisionincludesalloftheoceanwaterscoveringthebenthicdivision. Horizontally,thepelagicdivisionissubdividedintoanopen-sea(oceanic) province,andaninshore(neritic)province. Vertically,theoceanicprovincehasanupperlightedzoneanda lowerdarkzonewithnowell-markedboundarybetweenthetwo,For conveniencetheboundaryisarbitrarilysetat200m,sincethiswould correspondwiththearbitrarilysetdepthfortheedgeofthecontinental shelfandatthesametimeplacethelittoralsystemandtheneritic provinceinareasdefinitelywithinthelightedportion.Actually,light changesgraduallyinbothquantityandqualityfromtheverysurface downwardtodepthswhereitisnolongerdetectable(p.82),andthis "depthvarieswithlatitude,season,amountofsuspendedmaterial,living ordead,andthereforealsowithdistancefromshore.Thesevariables ofthepelagicenvironmentareofprofoundimport~ncetothepopulation ofthesea,aswillbepointedoutlater. Theoutstandingfeaturesoftheoceanicprovincearethebroad spatialexpansesandthegreatrangesofdepth.Asdistinguished fromtheneriticprovincethewatersareasaruleverytransparent,with littleornodetritusofterrestrialorigin.Thesewatersarepredominantly blueincolorandsupportthebluesurfacefaunatobediscussedmore fullyinchapterXVII.Althoughsolarlightpenetratesrelativelydeeper thanininshorewaters,thegreatdepthofthewaterincludedinthis provinceresultsincompleteeliminationofsolarlightbthedeeperportion
THESEAASABIOLOGICALE?WRONMENT279
oftheprovince,andasaresultonlycarnivoresanddetritusfeedersoan existintheverydeeplayers. Thechemicalcompositionoftheoffshorewaterisrelativelystable. SaEnityisuniformlyhigh,withonlysmallfluctuationsinspaceandtime (p,123),andplantnutrientsarefrequentlyrelativelylowintheupper layerandonlyslowlyreplaced. Theverticalborderseparatingtheneriticprovincefromtheoceanic issetattheedgeofthecontinentalshelf;henceallwaterofUepths shallowerthan200mwouldfallwithintheneriticprovince,which accordinglymayextendfarseawardininstanceswherethecontinental shelfisbroad,asofftheeastcoastoftheUnitedStates,orbeverynarrow, asoffthewestcoastofSouthAmerica. Althoughbiologicallyandchemicallytheborderbetweentheoceanic andtheneriticprovincesisnotstrictlydefinable,yetasweapproach thecoasttheplantandanimallifetakesoncharacteristicsnotfound inthetypicallyoceanicprovincewhere"blue-sea"formsprevail.The chemicalconstituentsoftheseawaterintheneriticprovincearemore variablethanintheoceanic.Salinitiesareusuallylower,sometimes markedly,andundergoseasonalorsporadicfluctuationssuchthatmany oftheinhabitantsaremoreorlesseuryhdineinnature-thatis,ableto endurewiderangesofsalinity.Riverwatermaybringinnutrients andmayAlsoexertastabilizinginfluenceontheturbulentmotion,being attimes,therefore,instrumentalininitiatingplantgrowthintheupper layers(p.789).Plantnutrients,nitrates,phosphorus,andsoonaremore readilyavailableintheshallowerinshorewaterbecauseofthegreater possibilityofreturnbyverticalcurrentsaftertheyhavebeenregenerated fromthedishtegratingorganismsonthebottomorinthedeeperwater (chapterVII).Thisfactorisoftheutmostimportancetoproductionof diatoms,foremostoftheprimaryfoodofthesea.Therefore,perunit arewofthesea,theneriticprovinceisfarmoreproductivethanthe oceanicprovirweandiseohaequentlytheregionofgreatestimportanceto marinelifeingeneral.Herefishofgreateeteconomicimportanceare taken,notonlybecauseofgreateravailability,butalsobecauseitis theirnaturalhabitat. OTHERBIOTICUNITS.Theaboveclassificationofthemarine environmentsisbaeedmainlyonbroadgeographical,physical,chemical, andbiologicalcharacteristicsthatcircumscribemoreorlessclearly theseparatezones.Withineachoftheseextensivezonesweobserve manyandvariedsetsofecologicalconditionsresultingfromdifferencesin substratum,proximitytoshore,depthandchemical-physicalconditionof thewater,andsoforth. Theprimary"topographic"unitusedinecologicalclassification oftheenvironmentisthebiotope,orniche,whichisdefinedas"anareaof whichtheprincipalhabitatconditionsandthelivingformswhichare
280THESEAASABIOLOGICALENVIRONMENT
adaptedtothemareuniform"(Hesse,Allee,andSchmidt,1937).Since inanygiventypeofbiotopethehabitatconditionsmakespecificdemands ontheinhabitants,itfollowsthatananalogousdevelopmentofthe inhabitantsisfrequentlyreflectedinthepopulation,andthosenotfitted forthehabitatareeliminatedfromit.Obviously,someorganismsare notsonarrowlyboundtothebiotopeasareothersofmorespecialized nature.
Thus,withinabiotopemaybefoundsomegeneralizedforms
suchascertaincephalopodsandfishesthatwandermoreorlessfreely fromonetypeofbiotopetoanother.Themorespecializedabiotope becomeswithrespecttolivingconditions,themoreuniformwillthe inhabitantsbecome,sothatonlyafewspecieswithlargenumbersof individualsmayexist.Thesmallerhabitatanomaliesfoundwithin thebiotopearecalledjacies.Thenumberoforganismsthatcanlive inanygivenbiotopemayinspecialcasesbedeterminedbyavailable suitablespace,butmorefrequentlyitwilldependuponthefoodsupply thatmaybeproducedwithinthebiotopeorbecarriedtoitfromoutside bycurrents.Thecommunityofformsinabiotopeiscalledabiocoenosis, Biotopeshavingcertaincharacteristicsincommon - forexample,. proximitytothecoastorestuarinelocality - areunitedintolarger divisionsknownasMochores. GeneralCharacterofPopulationsofthePrimaryBioticDivisions Underthepreviousheadingswehavedealtwiththeclassification ofthemarineenvironment.Forpurposesoffuturediscussionitisdesir- ableatthispointtooutlinebrieflyabroad,highlypracticalclassification ofthemarinepopulationinhabitingtheaboveprimarybioticdivisions, aclassificationbasednotonnaturalphylogeneticortaxonomicrelation- ships,asgivenonp.282,butratheronanartificialbasis,grouping heterogeneousassortmentsoforganismsdependinguponcommonhabits oflocomotionandmodeoflifeanduponcommonecologicaldistribution. Onthesegroundsthepopulationoftheseamaybedividedintothree largegroups - namely,thebenthos,nekton,andplankton,thefirst belongingtothebenthicregionandtheothertwotothepelagicregion. Inthebenthos(Gr.,deepordeep-sea)areincludedthesessile,creeping, andburrowingorganismsfoundonthebottomofthesea.Representa- tivesofthegroupextendfromthehigh-tideleveldownintotheabyssal depths.Thebenthoscomprises(1)sessileanimals,suchasthesponges, barnacles,mussels,oysters,crinoids,corals,hydroids,bryozoa,some oftheworms,alloftheseaweedsandeelgrasses,andmanyofthediatoms, (2)creepingforms,suchascrabs,lobsters,certaincopepods,amphipods, andmanyothercrustacea,manyprotozoa,snails,andsomebivalves andfishes,and(3)burrowingforms,includingmostoftheclamsand worms,somecrustacea,andechinoderms.
THESEAASABIOLOGICALENVIRONMENT281
Thenekton(Gr.,ewinwnhg)iscomposedofswimsnhganimalsfound inthepelagicdivision.Inthisgroupareincludedmostoftheadult squids,fishes,andwhales-namely,allofthemarineanimalsthatare abletomigratefreelyoverconsiderabledistances.Obviously,thereare noplantsinthisgeneralgroup. Inthepkwddon(Gr.,wanderer)isincludedallofthefloatingor driftinglifeofthepelagic.divisionofthesea,Theorganisms,both plantandanimal,ofthisdivisionareusuallymicroscopicorrelatively small;theyfloatmoreorlesspassivelywiththecurrentsandaretherefore atthemereyofprevailingwatermovements.Manyoftheanimalsare abletomakesomeprogressinswimming,althoughtheirorgansof locomotionarerelativelyweakandineffective.Theplanktonisdivided intotwomaindkisions,thephytoptinktonandthezooplankton.The formercomprisesallofthefloatingplants,suchasdiatoms,dinoflagellatesj coccolithophores,andsargassumweeds.Inthezooplanktonareincluded (1)myriadsofanimalsthatlivepermanentlyinafloatingstate,and (2)countlessnumbersofhelplesslarvaeandeggsoftheanimalbenthos andnekton.Sincetheplanktonandnektonoccupythesamebiotic realmandarepartofthesamecomrnunity,itisnecessaryalwaysto rememberthatthedistinctionisonebasedprimarilyonrelativesizeand speedofswimming,anddoesnotsignifyadivergenceofecological relationship. Eachofthesethreeecologicalgroupswillbemorefullydiscussedin laterchapters.
DevelopmentoflifeintheSea
Letusreviewbrieflytheobservationsthatindicatetherelative antiquityofthemarineenvironmentasabiologicalrealm.Itisnot possibletoknowwhenlifearoseinthesea,buttheclosesimilarityofthe chemicalcompositionofbodyfluidsandseawaterhasledtothesup- positionthattheseawasalreadysalineatthatearlytimeandthat, becauseoftheintimacyofprimitiveorganismswiththefluidenviron- ment,theelementspresententeredintothefmdamentalcomposition andmodeofmetabolismoftheprimitiveorganismsandaremaintained inpresent-dayformswithcertainmodific@ionsintheproportionsofthe primipalions,especiallymagnesium(table55).Theseinteresting relationshipshaveledtomuchspeculationrelativetothedevelopmentof organismsandthechemicalcompositionofprimitiveseas,butwecannot enterfurtheruponthatphaseoftheactionoftheenvironment.Peame (1936)hasgivensomereviewsandlistedliteraturepertainingtothese questionsandtothetheoryofmigrationofanimalsfromseatoland. Thepartplayedbytheseainthedistributionandmaintenanceof present-daylifeuponourglobeisavitalone.Theseaitselfisabundantly populated,andnolifecouldexistonlandwereitnotfortheperpetual
282THESEAASABIOLOGICALENVIRONMENT
watercycleofevaporation,precipitation,anddrainagebetweenseaand land.Onlyintheseawoulditbepossibletoapproachanydegreeof self-sufficiencyasabiologicalrealm,andhistoricallytheseahasacteda principalroleinthedevelopmentofanimallife. Thattheseaistheoriginalenvironmentofanimallifeisstrongly indicatedbycertainfactsthatpointtothegreaterageofmarinelife ascomparedtoterrestrialandfresh-waterfaunastowhichithasseem- inglygivenrise.Evidencepointingtoagreaterageofmarinefauna overtheterrestrialandfresh-waterfaunasismainlyalongfourlines: (1)generalcompositionofpresent-dayfaunas,(2)similarityinthe chemicalcompositionofbodyfluidsandseawater,(3)lifehistories, and(4)paleontologicalrelationships. (1)Thewholeanimalkingdomisdividedintoanumberofprimary divisions,eachknownasaph@.m.Eachphylumiscomposedofanimals havingcertainfundamentalmorphologicalsimilaritiesnotpossessedby anyanimalsofotherphyla.Thus,anatural,asopposedtoartificial, relationshipisindicated.Eachphylumisthendividedintonatural butmorerestrictedgroupsknownasclasses,andtheseinturnarefollowed byotheryetlowerdivisionsinthefollowingmanner:
Phylum
class Order
Family
Genus
Species
Speciesareformedofindividuals,andthemorphologicalfeatures bywhicheachspeciesischaracterizedarelessfundamentalandpresum- ablyofmorerecentoriginthanthosecharacterizingthegenera.Simi- larly,thegenericstructuresarelessfundamentalthanthoseoffamilies, andsoontothehighestdivision,whichisbasedonstructuresofgreat antiquity. Areviewofallthehigherormajordivisions - namely,thephyla andclassesofanimallife-revealsthestrikingpreponderanceofmarine groups.Alloftheseventeenphyla(usingthetaxonomicrankingofH.S. Pratt,1935,inManualojInvertebrateAnimals)arerepresentedinthe sea,andmost,ifnotall,arebelievedtohaveoriginatedthere.The followingfiveareexclusivelymarine:Ctenophora,.Echinodermatu, Phoronidea,Brachiopoda,C'haetogaatha.Someauthorsrecognizefewer thanseventeenphyla,butthishasonlytheeffectofincreasingthepre- ponderanceofpurelymarineclasses. Oftheforty-sevenclasses(whereonlysubphylaweregivenunder phyla,theyarehereratedasclasses)ofinvertebratesasgivenbyPratt, twenty-one,or43.7percent,areexclusivelymarine,andonlythree,or
THESEAASABIOLOGICALENVIRONMENT283
6.2percerit,areexclusivelynonmarine.OfthesubphylumVertebrate,
mdymembersoftheclassAmphibiaarenonmarine,whiletheotherfour classessharemembersinbothmarineandnonmarineenvironments. Thefishesarepredominantlymarine,whilethereptiles,birds,and mammalsarepredominantlyterrestrial.Theamphibiansrepresent thehighestnonmarinegroup. Theeedivisionsdemonstratetheastonishingvarietyofmarine animals,asfarasthemajorphylogeneticgroupsareconcerned.How- eve~theterrestrialenvironmentharborsthegreatestnumberofspecies, mainlyowingtothelargenumberofspeciesofonerestrictedgroup, theinsects,whicharealmosttotallyabsentfromthesea.Thepresence intheseaofsomanymajorgroups,manyofwhicharerestrictedtothe sea,indicatesthegreattendencyonthepartofthemarineenvironment topreservethegroupsthathaveoncebecomeevolved. Itshouldbenotedalsothat,inadditiontotheremarkablediversity ofmarinelifeintheocean,thereisaconspicuousprimitiveelement, asjudgedbysimplicityofstructure,inthegroupsrepresented.In theseathereisamorecompletedevelopmentalseriesofanimallifethan existsanywhereelse,becauseofwhich,andalsobecauseofthenatural andiritimaterelationshipsoftheorganismstothesea-watermed~um,the studiesissuingfromthemarinebiologicallaboratorieshavecontributed vastlytoinformationonbiologicalproblemsdealingwithdevelopment andmaintenanceoflife. Therelativeuniformityofthemarineenvironmenthasbeeninstru- mentalnotonlyinpreservingthediversityofformsbutalsoinretaining agenerallymoreprimitivecharacterascomparedwithterrestrialand fresh-wateranimals.Itistruethatintheseawedofindassociated withthelowerformsanumberofhighlydevelopedanimalsthatmustbe consideredmarinebecauseoftheirdependenceonthesea.Theseare theseals,whales,certainreptiles,fishes,andbirds.Allofthesegroups, however,havehadalargepartoftheirracialdevelopmentintheterres- trialandfresh-waterhabitat.Theyhavemorerecentlyrevertedtothe seaandhaveonlysecondarilybecomeadaptedtoit.Theteleostfishes, whicharebelievedtohaveevolvedtotheirpresentstatusinfreshwater, wereoriginallyderivedfrommarinestock. (2)Therelationofbodyfluidstoseawaterhasalreadybeendie. cussed(p.269). (3)Astudyofthelifehistoriesofinvertebratessuggeststheantiquity ofmarineliie.Duringtheearlyhistoryoftheindividualsofsome animalgroupsthelarvalstagesaremarkedlydifferentinstructureand habitfromthematurephase.Thelarvalstages,whichsometimes resemblethematurestagesofothergroupsoroniythelarvaeofother groups,arethoughttoreflectastructuralsimilaritytoancestralstock. Whetherornotthkisarealrecapitulationofracialhistoryoronlyan
284THESEAASABIOLOGICALENVIRONMENT'
expressionofindividuallarvaladaptationtoacommonenvironmentis importantinseekinganunderstandingofthesimilarity.Whatever thetruthmaybe,itiswellknownthatmostmarineinvertebratespass throughanearlystageduringwhichthelarvaeinnowaystructurally suggesttheirparentage,butmayevenhavestrikingfundamental similaritytoexistinglarvaeofothergroups.Fromthisithasbeen possibletoestablishtypesoflarvae-forexample,thetmchophoreof theAnnelidaandMollusca,andthenuupliusofthecrustaceangroups (fig.80,p.321). Thereisatendencyforsomeaggressiveanimalgroupstodesert theseaforfresh-waterorlandhabitats.Thwisshownbythecrusta- ceans,amongwhichthereareformssuchastheprawn,Zh-iocheir,which entersfreshwateratayoungstagebutwhenmaturereturnstothesea tospawn.Thelandcrabs,Cardisoma,Gecarciwa,andsoforth,also gothroughafree-swimminglarvalstageinseawater. (4)Itiswellknownthatanimalfossilsoccurringintheoldestknown fossiliferousrocksoftheearth'scrustaremainlymarineforms. MarineanimalswereabundantandbecamefossilizedintheCambrian period(500millionyearsago),whencertainportionsofthelandhow abovesealevelformedapartoftheseabottomalongthecoastsofancient seas.Severalinvertebratephylawerealreadydeveloped,andsuch formsastrilobitesandbrachlopodswereparticularlyabundant. Thechiefrolesofthemarineandterrestrialenvironmentsinthe developmentoflifemaybesummarizedbysayingthatthegreatpart playedbytheformerischieflyinthedevelopmentandmaintenanceofa widediversityoflowerforms,whileinthelattertheinfluenceofthemore rigoroushabitatshasproducedlessdiversityofformbutahighertype ofcomplexity. Theareawherethesetwogreatenvironmentsmeet,theintertidal zone,isinanintermediatepositionandsubjecttorapidandmarked vicissitudes,anditisfromherethatmuchofthemigrationtolandis supposedtohavetakenplace.
Bibliography
Bethe,A.1929.
IonendurchlassigkeitderKorperflachevonwirbellosen
ThierendesMeeresalsUrsachederGiftigkeitvonSeewasserabnormer
Zusammensetzung.PflugersArch.,221,p.344-362,1929.
Dakin,W.J.1935,Theaquaticanimalanditsenvironment.LinneanSot. NewSouthWales,Proc.,v.60,pts.1,2,p.viii-xxtil,1935. Ekman,Sven.1935.TiergeographiedesMeeres.Akad.Verlagsgesellsch.,
IApzig.542pp.,1935.
Gklen,T.1930.EpibiosisofGullrnarFjord.II.KristinebergsZOOLSta.
1877to1927,No.4,p.1-380,1930.
Hesse,Richard,W.C.&lee,andK,P.Schmidt.1937.Ecologicalanimal geography.Anauthorized,rewritteneditionbasedon"Tiergeographle aufoekologischerGrundlage,"byRichardHesse.JohnWiley&Sons.NewYork.597pp.,1937,
THESEAASABIOLOGICALENVIRONMENT285
Hewatt,WillisG.1937.Ecologicalstudiesonselectedmarineintertidal communitiesofMontereyBay,California.Amer.Midland
Naturalist,
V.18,p.161-206,1937.
Keys,Ancel.1933.Themechanismofadaptationtovaryingsalinityinthe commoneelandthegeneralproblemofosmoticregulationinfishes.Roy.
Sot.,Proc.,B,v.112,p.184-199,1933.London.
Macallum,A.B.1926.Paleochemistryofbodyfluidsandtissues.Physiol.
Rev.,v.6,p.316-357,1926.
Pantin,C.F.A.1931.Origin'ofthebodyfluidsinanimals.BioLReviews, v.6,p.459-482,1931.Cambridge,England. Pearse,A.S.1936.Themigrationsofanimalsfromseatoland.Durham,
N.C.,DukeUniv.Press,176pp.,1936.
Pratt,HenryS.1935.Amanualofthecommoninvertebrateanimalsexclusive ofinsects.Revised.Philadelphia,Blakiston,854pp.,1935. Shdford,V.E.,etal.1935.SomemarinebioticcommunitiesofthePacific CoastofNorthAmerica.Pt.1.Generalsurveyofthecommunities.
Eool.Monographs,v.5,p.250-332,1935.
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