THE SECRET LIFE OF THE OCEAN

THE SECRET LIFE OF THE OCEANCompiled by M. A. González

Left: Obelia sp.

CONTENTS

Introduction 01

Taxonomy: 06

01NanoplanktonicFlagellates 09

02Cnidarians 09

03PhylumRotifera 11

04Polychaeta 11

05MarineGastropods 13

06Chaetognatha 13

07Tunicates 13

08Cladocera 15

09Krill 15

10InsectLarvae 15

11Copepods 17

LivinginGroups: 18

Apaptations 19

NightSwimming 20

CommunitiesofZooplankton 21

Colphon 24

Left: Obelia sp.

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Zooplanktonarethetinyanimalsthatfloataroundonthesurfaceoftheoceanandfeedonthemicroscopicplantsthatmakeupthephytoplankton,oroneachother.Theyaresosmallthattheycannoteasilybeseenandsoformostpeopletheydon’tevenexist.Butwhatwouldhappeniftheydidn’t?

Wehavecluesfromthefossilrecord.AttheendofthePermiantherewasahugeextinctioneventthattookoutanestimated95%ofalllivingspeciesatthetime.Again,attheendoftheCretaceous,therewasanothermassiveextinctioneventwhichtook

outnotonlyallthedinosaursbutmanyotherspeciesaswell,includingthemajorityoflargemarinespecies.ThecausesoftheseextinctioneventsarestilldebatablealthoughthereisstrongevidenceforameteorstrikeattheendoftheCretaceous.Whatdoesseemevidentisthatwholeecosystemscollapsedbecausethefoodchainscollapsed.Whentheplantsandanimalsatthebottomofthefoodchaindiedintheirmillionsorevenbillions,animalsfurtherupthefoodchaindiedoutforlackoffood.Eveniftheysurvivedtheinitialcatastrophe,theystarvedintheyearsofdearthfollowing.

Thisiswhatwouldhappentothemarineecosystemsifsomethingweretohappentothezooplankton.Evennow,thiscanbeseeninthephenomenonknownasElNino,whenthecurrentsoffSouthAmericachange.NormallythereareareasofupwellingoffPeruwherenutrient-richcoldwatersrisetothesurface,whichleadstoplanktonbloomswhichfeedthefish.WhenanElNinoeventoccurs,thecurrentschange,theupwellingdoesnotoccur,theplanktonbloomsfailandthefisheitherstarveormoveelsewhere.Otheranimalssuchaspenguinsandsealsarealsoaffectedandmanychicksand

INTRODUCTIONBy Marine Biologist M. E. Skeel

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pupsunluckyenoughtobeborninsuchyearswillstarve.

Halfthewhalesoftheworldarebaleenwhalesandtheyaretotallydependentuponphytoandzooplanktonfortheirfood.Thesewhalesaremigratory,goingtowarmtropicalwaterstoraisetheirbabies.ThentheytravelgreatdistancestoareasofupwellingincolderwaterssuchastheSubantarcticConvergencewhereplanktonthriveonrisingnutrients.Ittakesmillionsofplanktonicorganismsineachmouthfultosustainahumpbackwhale.Tosustainanentirepopulationofeven

onespeciesofbaleenwhalestakesbillionsofplanktoneveryyear.Eachwhalehastoeatenoughtosustainitselfnotonlyforthesixmonthsoffeedingbutafurthersixmonthsoftravel,breedingandchildrearinginnutrientandfood-poortropicalwaters.

Arephytoplanktonenoughtosustainthewhales?Apparentlynot.Whattheyneedarekrill;millionsandmillionsoftinycrustaceansthatresembleshrimp.TheseanimalsarethebasisoftheentireAntarcticfoodchain,supportingthefish,thesharks,penguins,sealsandwhales.Removethesetiny

animalsandpotentiallytheentireecosystemwouldcollapse,withdireconsequencestoalltheselifeforms.

Soarethezooplanktonoftheworld’soceansinanydanger?Itdoesn’tlooklikewearegoingtobehitbyameteoranytimesoonbutthereisadangerclosertohome:ourselves.Aswedepletetheoceansofthelargerfish,wearefishinglowerandloweronthefoodchain.Nowlargefactoryshipsarebeginningtotakekrill.Someofitgoesforfertilizersandalotofitendsupinpetfood.Afewpeoplearemakingalargeprofitonthese

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tinyanimals.Butifweoverfishthezooplanktoncommunities,weriskthecollapseoftheoceansecosystemsandthenwewillfindoutjusthowimportantzooplanktonare.

Noctiluca scintillans

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Zooplankton aretinyanimalsfoundinalloceanzones,particularlythepelagicandlittoralzonesintheocean,butalsoinponds,lakes,andrivers.They are a key component of marine ecosystems.

ZOOPLANKTON:(zoh-plankton)

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Zooplanktonsareclassifiedbysizeandbydevelopmentalstage.Sizecategoriesinclude:picoplanktonthatmeasurelessthantwomicrometers,nanoplanktonmeasurebetweentwoto20µm,microplanktonmeasurebetween20µmupto200µm,mesoplanktonmeasurebetween0.2mmupto20mm,alsomacroplanktonmeasurebetween20mmto200mm,andthemegaplankton,whichmeasureover200mm(almost8inches).Therearetwocategoriesusedtoclassifyzooplanktonbytheirstageofdevelopment:meroplanktonandholoplankton.Meroplanktonsareactuallylarvaethateventuallychange

TAXONOMYInformation by marinebio.org

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intoworms,mollusks,crustaceans,coral,echinoderms,fishes,orinsects.Holoplanktonremainplanktonfortheirentirelifecycle,andincludepteropods,chaetognaths,larvaceans,siphonophores,andcopepods.

Meroplanktonandholoplanktonarecomponentsofalmosteverytaxonomicgroup.However,themostcommon

planktonareprotists,nanoplanktonic

flagellates,cnidarians,ctenophores,

rotifers,chaetognatha,veligerlarvae,

copepods,cladocera,euphausids,

krillandtunicates.Protistsproduceenergybyphotosynthesisandformthe

baseofmarinefoodwebsasprimaryproducers.Protozoaarealsoprotistsandaresimilartoanimals.Protozoamakeupahugepartofmicroandnanozooplankton,suchasamoebas,ciliates,andflagellates.Theseanimalsdonotphotosynthesizeenergy.SomeamoebassuchasthoseclassifiedasForaminiferaandActinopodahavehardskeletons,usuallylargerthan2millimetersindiameter,thathelpformdeep-seasediment.

8Protozoa with mixed Ciliates

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01 02Zooplanktonalsoincludethenanoplanktonicflagellatesthathelpkeepbacteriapopulationsundercontrol.Theyarecharacterizedbyeitheralongtailusedforswimming(flagellates)orbyhair-likestructurescalledcilia(ciliates).Somedinoflagellateshaveanet-likestructurecalledaprotoplasmicnet—usedtocaptureandeatpreythataretypicallylargerinsizethanbacteria.Somedinoflagellatespeciesarealsoresponsibleforharmfulfishkillsandtheinfamousredtides.Ciliatesarecapableofcatchingbacteria,otherprotistsandphytoplankton.

Mixotrophsareanamazingorganismthatarehalfplantandhalfanimal.Mixotrophshavetheabilitytoingestotherorganismsthroughphagocytosis(phago:“toeat”+cytosis:“cells”=theprocessofengulfingothercellsforingestion)butalsocontainfunctionalphotosyntheticstructures.

NANOPLANKTONIC FLAGELLATES

Cnidariaisaphylumthatcontainsthecolonialsiphonophoresandthescyphozoans—alsoknownasthetruejellyfish.Bothoftheseanimalsarepredatorsandhavestingingtentacles.Theyarenotfoundofteninfreshwaterandintheoceantheyinhabitthelayersclosertothesurface.CombjelliesorctenophoreswerepreviouslyclassifiedunderCnidariabuthaverecentlybeendistinguishedfromotherjellyfishbecausetheylackthecharacteristicstingingcellsofotherjellyfishknownasnematocysts.Combjellieskeepcopepodzooplanktonlevelsincheckthroughpredation.

CNIDARIANS

10Cnidarians

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03 04PHYLUM ROTIFERA

Thereareabout2,375speciesofrotifersinfreshwaterandonly125intheocean.Mostoftherotifersarenon-motile(notabletomove)butabout100speciesareholoplanktonic.Theyusuallyeatbacteria,detritus,otherrotifers,algaeorprotozoa.Rotifersarehighlyefficientreproducers.Theyareabletoreproduceasexually(withoutamate)whenenvironmentalconditionsaregood,andsexuallywhenenvironmentalconditionsarestressful.Thisabilityallowsrotiferstoconserveenergyingoodconditionsandadapttotheirenvironmentinstressfulconditions.Adaptationispossiblethroughsexualreproductionbecauseavarietyof

offspringareproduced,allowingtheindividualsbestsuitedtotheenvironmenttosurvive.

Thesetinyanimalsarequiteuniquebecausetheydemonstrateincrediblecomplexityincomparisonwithorganismsofasimilarsize.Thedistinguishingfeatureofarotiferisitscorona,acollectionofciliashapedlikeawheelaroundtheheadendoftheorganism.Astheciliamove,theycreateacurrentwhichsucksinfoodfortherotiferandhelpsittonavigate.

POLYCHAETA

ThePolychaetaorpolychaetesareaclassofannelidworms,generallymarine.Eachbodysegmenthasapairoffleshyprotrusionscalledparapodiathatbearmanybristles,calledchaetae,whicharemadeofchitin.Polychaetameans“many-bristled”(asopposedtotheOligochaetawhichare“few-bristled”),andindeedthepolychaetesaresometimesreferredtoasbristleworms.Morethan10,000speciesaredescribedinthisclass.Commonrepresentativesincludethelugworm(Arenicolamarina)andthesandwormorclamwormNereis.

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05 06 07ThechaetognathaorArrowwormsaremostlyholoplanktonicandareabundantworldwide.Thesetransparentwormsareapproximately3cmlongandhavefinsonthesidesoftheirbodies.

MARINE GASTROPODS

Anothertypeofzooplanktonincludethelarvaeofbenthicmollusksusuallyfoundincoastalwaters,suchasmarinegastropodsincludingheteropodsorpteropods.

CHAETOGNATHA TUNICATES

Sometunicatesareplanktonic,suchastheholoplanktonicclassesAppendiculariaandThaliasia.Botharefilterfeeders;Appendiculariaconsumessmallfoodparticlesusingamucousfilter.Othertypesoftunicatesarebenthicandareonlyplanktonicduringtheirlarvalstages.

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Heteropods Thalia democratica Arrow worm

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08 09 10CLADOCERANS

Claudoceraarefoundincoastalwaters.Theyswimusinganantenna,likecopepods,butinsteadofusingtheirfirstantenna—theyusethesecondantenna.Theyappeartohavetwosectionstotheirbodybutit’sonlyanillusioncausedbyafoldedoutershell.Cladoceranseatphytoplanktonandotherzooplankton.Likemanyspeciesofzooplankton,cladoceransmigratetothesurfaceatnight.Thisisreferredtoas“diurnalmigration”.

KRILL (Euphausia superba)

INSECT LARVAE

ThelarvaeofthemidgeChaoborusistheonlywidelyknowninsectlarvaeclassifiedasplankton.Chaoboruscomesupduringthenighttofloatwithotherplanktonandeatsmanytypesofzooplanktoninlakes.

Krill,classifiedunderEuphausids,arefoundallovertheworld.Theycanbe3cmlargeandareanimportantsourceoffoodformanytypesofwhales.Incoldwaters,krilloftenfeedondiatoms,atypeofphytoplankton.Inwarmerwatertheyeatotheranimals.

(Phylum Arthropoda, Subphylum Crus-tacea, Order Copepoda)

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Rotifers Krill Ciliates

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11Mostmacrozooplanktonarecopepodsfoundinmarineandfreshwaterecosystems.Copepodsswimusinganantennaandfrontalstructuresontheirbodies.Theyeatphytoplanktonanddetritus,andoccasionallyotherzooplanktonsmallerinsize.

COPEPODS(Phylum Arthropoda, Subphylum Crus-tacea, Order Copepoda)

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LIVING IN GROUPS

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Allspeciesofplanktonhavebeenforcedtodevelopcertainstructuraladaptationstobeabletofloatinthewatercolumn.Adaptationsinclude:flatbodies,lateralspines,oildroplets,floatsfilledwithgases,sheathsmadeofgel-likesubstances,andionreplacement.Theflatbodyandspinesallowsomespeciesofplanktontoresistsinkingbyincreasingthesurfaceareaoftheirbodieswhileminimizingthevolume.Allotheradaptationskeepplanktonfromsinkingquicklytothebottom.Zooplanktonhavealsoadaptedmechanismstodeterfish(theirheaviestpredator)including:

transparentbodies,brightcolors,badtastes,redcoloringindeeperwater,andcyclomorphosis.Cyclomorphosisoccurswhenpredatorsreleasechemicalsinthewaterthatsignalzooplankton,suchasrotifersorcladocerans,toincreasetheirspinesandprotectiveshields.

ADAPTATIONS

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Manytypesofzooplanktonmigratedeeperintothewaterduringthedayandcomeupatnight.Themigrationofspeciesappearstobedependentonlocationratherthanparticularspeciestypes.Allplanktonmigratedifferentlybasedonfactorslikeage,sexandtheseason.Theamountoflightisprobablythemajorfactorintheextentofmigratorybehavior.Itseemsthatzooplanktonmovearoundmostinlowlightandleastinhigherlightsituations.It’spossiblethatzooplanktonmigratetolowerlevelsduringthedaysotheyarelessvisibletopredatorsrelyingonvision.At

night,zooplanktoncansneakuptothesurfaceandsnackonphytoplanktonrelativelysafely.Thelowermetabolismoccurringincolderwatersduringthedaymayalsobeafactorinthemigrationofzooplankton.Thisway,zooplanktoncansaveenergybyfeedinginthecooler,nightwaters.Thefactthatdifferentspeciesofzooplanktonhavevaryingmigrationtimesseemstobetheresultofapartitioningofresources.

NIGHT SWIMMING

Copepods

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Specificspeciesofzooplanktonoccupyparticularmarinehabitats.Eachspeciesisuniquelyadaptedtofactorslikelight,temperature,turbulence,andsalinityinitsenvironment.ZooplanktonononesideoftheGulfStreamaredifferentspeciesfromthoseontheotherside.Thesecharacteristicsofdifferentspeciesofzooplanktoncansometimeshelpscientistsdistinguishonewatermassfromanother.

Zooplanktonarealsosensitivetotheirenvironmentandlikephytoplankton—achangeinzooplanktonconcentrationcanindicateasubtleenvironmental

change.Zooplanktonarehighlyresponsivetonutrientlevels,temperatures,pollution,foodthatisnotnutritious,levelsoflight,andincreasesinpredation.Aswellasprovidinganessentiallinkinthemarinefoodchain(whichisanunderstatement),thediversityofspecies,amountofbiomassandabundanceofzooplanktoncommunitiescanbeusedtodeterminethehealthofanecosystem.

Thereareotherfactorsthatinfluencethedistributionofzooplanktonlikepredation,reproduction,communityinteractionsandtheamountof

COMMUNITIES OF ZOOPLANKTON

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availableresources.Zooplanktoncanalsobepredatorsofalgaeorprotozoacausingthesizesoftheseorganismstochangethroughevolution.Whenlightconcentrationsinborealortemperateareasincreaseinspring,phytoplanktoncommunitiesincreaseinnumber.Becausezooplanktonfeedonsmalerplanktonslikephytoplankton,thenumbersofzooplanktonincreaseinresponseduringthespring.However,thereactionofzooplanktonisdependentonthespeciestypeaswell,sosometimesthezooplanktonnumbersincreaseonlyinthesummerwithotherspikeinthefall.

ZooplanktonarealsoaffectedbylevelsofpH,heavymetals,calcium,andaluminum.Nutrientslikenitrogenandphosphoruswillaffectthepreyofzooplankton(likealgae,protozoaandbacteria),indirectlyaffectingzooplanktonsurvival.Scientistsarestillputtingtogetherpiecesofthezooplanktonpuzzle.Somequestionsincludehownutrientlevelsfoundinalgaecaninfluencethegrowthandbehaviorofzooplankton.Otherquestionsconsideredimportanttomarineandhumanlifeishowtoxinsandpollutionisaffectingthiscruciallinkinthefoodchain.

Chaoborus

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Marinebio.orgReferences

Dinoflagellates-AndrewMacRae,PalynologyatTheUniversityofCalgaryDept.ofGeologyandGeophysicsKrill:ChesapeakeBayProgramZooplanktonProjectZooplanktonEcology-DepartmentofFisheriesandAquaticSciences,UniversityofFloridaRobertW.Sanders,“Zooplankton”,inAccessScience@McGraw-Hill,http://www.accessscience.com,DOI10.1036/1097-8542.756950

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GraphicDesignandSilkscreen

ParsonsTheNewSchoolforDesign

Professors:KatarzynaGruda

WilliamMorrisey

Design:MariaA.Gonzalez

Typefaces:AkzidenzGrotesk

BodoniOldFaceBE.

Software:InDesignCS4

Text:marinebio.org

M.E.Skeel(www.helium.com)

Images:Flickr

GuidetotheMarineZooplanktonof

southeasternAustralia.(http://www.

tafi.org.au/zooplankton/index.html)

COLOPHON

Noctiluca scintillans

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