Seasonal variability in plankton community structure, productivity and food web transfer along the salinity gradient of the Baltic Sea

ICESCM2009/A:11,1246 Nottobecitedwithoutpriorreferencetotheauthor  Seasonalvariabilityinplanktoncommunitystructure, productivityandfoodwebtransferalongthesalinity gradientoftheBalticSea by LutzPostel1,JavierArístegui2,SantiagoHernández‐Leon2,MayGómez2, CarlosAlmeida2,AgustinPortillo‐Hahnefeld2,MariaF.Montero2and TheodoreT.Packard2 1LeibnizInstituteforBalticSeaResearchWarnemünde,Germany 2FacultaddeCienciasdelMar,UniversidaddeLasPalmasdeGC,Spain Correspondingauthor:lutz.postel@io‐warnemuende.de, telephone:+493815197206,telefax:+493815197440  Abstract Thebrackishwaterenvironmentinthesemi‐enclosedBalticSeacauseschangesinplankton communitystructureincloserelationtolarge‐scalecirculationpatterns.Inaddition, seasonalchangesinnutrientslevelsandstoichiometricratios,lightandstratification successivelymodifiedit.Theanalysisofcomprehensivedatasetsonenvironmental properties,microandmeso‐planktoncommunities,theirmetabolicactivityandproductivity basingonclassicalandenzymaticmethodsallowsverifyingtheinterplaybetween communitystructureandfoodwebtransferfromKattegattotheGulfofFinlandinthe ninetynineties.Aspects,liketheratiobetweennewandregeneratedproduction,the percentageofprimaryproductivityutilizedbyheterotrophsofdifferentsize,andthe stoichiometryinnutrientregenerationbymesozooplanktonwereinvestigated.Regions wherenew(primary)productionwasdetectablewererestrictedtoareaswithriver dischargeafterthespringbloom,butdidneverexceedsomepercentagesofgross production.NitrogenandphosphorouswereexcretedbymesozooplanktoninN/P=6inMay andN/P=10inAugustinthesameregionbecauseofthelargerpercentageof parthenogeneticallyreproducingcladoceransinsummer.Herbivorousplankton<100µ utilizedonemagnitudemorematterofautotrophicorigin,thanlargerplankton.Although therewasamarkedvariabilityalongthezonalgradient,overallseasonalityexceeded regionalsalinitydrivendifferencesinfoodwebtransferandinthecommunitystructure.  Introduction Biochemical,especiallyenzymaticmethodsformeasuringproxiesofphysiologicalrateswere developedinthenineteenseventiesforexampleforrespiration(Electrontransportsystem [ETS]activitybyPackard,1969;OwensandKing,1975),ammoniaexcretion(Glutamate dehydrogenase[GDH]activitybyBidigareandKing,1981),andgrowth(e.g.Aspartat transcarbamylase[ATC]activitybyBergeronandBuestel,1979).Theuseofthesemethods becamemoreandmorepracticable(c.f.inHarrisetal.,2000).Incontrasttoclassicalincubation methods,analyseswerelesstimeconsuminganddislocatedfromshiptolandbased laboratories.Thereductionofinitialvolumesforvariousdeterminationspermitteddiverse measurementsfromthesamesourcematerial.Thisallowedamultidimensionalmappingof variousphysiologicalrates(e.g.Packard,1985)inparallelwiththequasi‐synoptic hydrographicalmeasurements. Resultsofenzymaticmethodsneedtobecalibratedbyclassicalapproachesmostlybasingon incubations.Bothtypesofmethodshavetheirspecialrestrictionsanddiscussionsontheir accuraciesarenotfullycompleted.Ontheotherhand,theparallelusehasalsopotentialsfor testinghypothesisoffundamentalrelevance,forexamplethemeaningofallometric relationshipsinplanktology(PackardandGómez,2008). Twentyyearsago,weusedtheenthusiasmduringtheprocessofEuropeanreunificationand associatedfundingtoexchangeideas,toshareknowledge,andtodeepenpartlyexisting researchco‐operations.Itresultedinalargerdatasetmainlyonplanktonrespiration,ammonia excretion,andgrowthcollectedduringcruiseswhentheLeibnizInstituteofBalticSeaResearch, Warnemünde,GermanyandpartlytheMarineScienceFacultyoftheUniversityofLasPalmas, G.C.,Spain,wereinvolved.Theactivitiesstartedin1989inthecentralpartoftheAtlantic Ocean(Hernández‐Leónetal.,1999),intensivelycontinuedintheBalticSea(Posteletal.,1992, 1995)andcoveredregionsinIndianOcean,aNorwegianFjord,andtheAngola‐Benguela‐ FrontalRegion(Fig.1).Currently,thematerialwillbeviewed,dataexperimentsperformedin ordertouseitforcomplexsolutions.Thespace‐temporalresolutionofdataishighestinthe BalticSea.Ontheotherhand,combinedstudiesoninteractionsincommunitystructureand mattertransferintheBalticSeaareratherrare(Sandberg,2007).Therefore,westartedinthis regionwithouranalysis.Laterwewillfocusoureffortsalsointhedeepseaareasandon methodologicalaspects. Methods Inprinciple,planktonoftheBalticSeawascollectedduringordinarymonitoringcruises betweenBeltSeaandGulfofFinlandin1990(Fig.2).Phytoplanktonfractionwascollectedby bottlesampleswhileWP2nettowsof55and200µmmeshsizeswereusedforzooplankton. Themetabolicbalanceinoxygenhasbeenmeasuredinmicro‐plankton(<100µm)fromstandard depthsdownto20musinganautomatedversionofthemicroWinklermethod(Arísteguiand Montero,2005).Calculationsofnewproductionbaseonaconceptualmodel.Itconsidersthe ideathatthephysiologicaluptakeofnitratebythephytoplanktoniscontrolledbythenitrate reductasereactionwhichwasmeasured.Zooplanktonsamplesweresievedintosizeclasses, splittedforbiomassdeterminations,speciesanalysesandmeasuringmetabolismbyenzymatic methodsandbyclassicalincubationmethodsonselectedstations(Posteletal.,1995; Hernández‐LeónandTorres,1997;Hernández‐Leónetal.,1995).Phytoplanktondatawereused fromIOWdatabase.MethodsonsamplingandanalysisaredescribedinWasmundetal.(2008). Searchingforreasonablegeographicaldifferencesinphytoplanktonandzooplankton communitystructuresintheupperlayer,weconductedsimilarityandclusteranalysesapplying BrayCurtissimilarityanalysis,squareroottransformationandcompletelinkageasthecluster modebyPRIMERsoftware(cf.,ClarkeandWarwick,1994).  ResultsandDiscussion Theactualsalinitypatternintheonemeterlevel(Figure3)seemstobetheresultofthelarge‐ scalecounter‐clockwisecirculationintheBalticproper.Planktoncommunitiesfollowedthis structure.Fourclusterswerefoundatthe50%similaritylevelusingzooplanktonabundanceand speciescompositionintheupperlayer(Figure4a).Theyshowananalogousdistributionwhen usingthe30%similaritylevel(Figure4b).Theresultrecurredforphytoplankton.Afterthesame analysis,thestationsgroupedinfivedifferentcategoriesatthe50%level(Figure5a)and showedasequenceofstationslikezooplanktonwhenusingthe30%similaritylevel(Figure5b). Inthisstageoftheanalysis,wehaven´tlookedforthedetailedinfluenceofdifferentcommunity structuresonmattertransfer. Theinvestigationsweredoneafterthephytoplanktonspringbloom.Therefore,newprimary productivitycalculatedfromnitratereductaseshowedsignificanthighervaluesinareasof externalnutrientsuppliesonlylikeintheOdrariverplumeandintheGulfofFinland(Figure6). Ingeneral,newproductionwasclearlysmallerincomparisontogrossproduction(seeunits). Consequently,thepercentageofnewproductiondidnotexceed5%ofgrossproduction,i.e. regeneratedproductiondominatedatthisstageofseasonaldevelopmentalready. ConvertingrespirationtocarbonandrelatedtoprimaryproductivityasdescribedinPosteletal. (1995),upto80%ofprimaryproductivitywasutilizedbyplankton<100µm,andabout6%by plankton>100µm(Figure7).Thispercentageexceptionallyincreasedupto38%insummer whenzooplanktonwasmoreabundant. Generally,insitu(Arrheniuscorrected)respirationofplanktonbetween100and200µmwasin turnwithexcretionexceptatsomestations(Figure8).Thiswasnotgenerallythecase,which mightbeofspecialinterest.Figure9reflectsthesituationoffOdraRiverinautumn.The situationwascharacterizedbyasalinityfrontinabout10nauticalmilesdistancetotheriver mouth(Fig.9a).Plantpigmentsdecreaseddrasticallyontheseasideoftheplume.Itfittedwith thespecificgrowthrateintermsofATCactivityunits(substrateutilization),whilethespecific respirationreachedmaximumvaluesinthefrontalarea(stress?).IncontrasttoFigure8, excretionactivity(GDH)didnotspatiallycorrelatewithrespiration.Itincreaseddownstreamthe frontalareawhenrespirationwaslow(Figure9b). Thestoichiometryinnutrientregenerationbymesozooplanktonwasnotinvestigatedindetail inourfirstattempt.AveragesofNandPregeneratedbyzooplankton<200µmshowed differencesinMayandinAugustaccordingtoPosteletal.(1995).TheratiowassmallerinMay (N/P=6)thaninAugust(N/P=10).Itcouldbeexplainedbydifferentplanktoncompositionand potentialdifferencesinenergyrequirementsforreproduction(Gismervik,1997).InAugust,the proportionofcladoceranswasmuchhigherthaninMay(Figure10)whichmaycauselargerP requirementsforenergyrichATPcompoundsduetotheirparthenogeneticreproductionmode. Byallmeans,thisshouldbecomeclearerwhendealingwiththeannualtimeseries(Table1).For thefuture,wealsoseepotentialsforansweringthequestion:Dochangesincommunities 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MorskiegoInstytutuRybackiego/BulletinoftheSea,RybackiegoInstitute136(3):61‐73. Sandberg,J.,2007.Cross‐ecosystemanalysesofpelagicfoodwebstructureandprocessesinthe BalticSea.EcologicalModeling,201(3‐4):243‐261 Wasmund,N.,Pollehne,F.,Postel,L.,Siegel,H.,Zettler,M.L.,2008.Biologische ZustandseinschätzungderOstseeimJahre2007.Meereswiss.Ber.Warnemünde74:1‐88.    TableandFigures  Table1:Reviewonzooplanktondatacollection(Project,when,where,parametermeasured, relatedaspects)  Figure1:Locationsofzooplanktonstudiesoncommunitystructure,metabolismandgrowthby enzymaticandclassicalmethodsbyLeibnizInstituteofBalticSeaResearch, Warnemünde,Germany,andpartlybyMarineScienceFacultyoftheUniversityofLas Palmas,G.C.,Spain Figure2:SamplinglocationsintheBalticSeainMay1990 Figure3:SalinitypatternintheonemeterlevelduringMay1990 Figure4:(a)Similarityplotbasingonabundanceandspeciescompositionofzooplankton> 100µmintheupperlayerinMay1990and(b)distributionofstationsrelatedonthe 30%similaritylevel Figure5:(a)Individualdominance(relativeabundance)withinfivephytoplanktonclusters duringMay1990intheupper20mand(b)distributionofstationrelatedonthe30% similaritylevel Figure6:Newversusregeneratedproductionofplankton<100µmintheupper20minMay 1990:Grossproduction,newproductioncalculatedfromnitratereductaseactivity,and thepercentageofnewproductionatgrossproduction Figure7:Percentageofprimaryproductivityutilizedbyplankton<100µmandbyplankton> 100µm(PBPomeranianBay,ASArkonaSea,BSBornholmSea,S&CGSSouthernand centralGotlandSea,NBPNorthernBalticproper,GoFGulfofFinland,WGSWestern GotlandSea,BS2BornholmSea2ndsurvey,AS2ArkonaSea2ndsurvey) Figure8:ComparisonofthecourseofinsituspecificETS‐andGDHactivityofthefraction100 to200µmbetweenthewesternBalticSea(station12)andtheGulfofFinland(station 305)andreturntoArkonaSea(station113)inMay,1990 Figure9:CourseoftheinsituspecificmetabolicratesandgrowthoffthenOdraRivermouthin fall1993:(a)salinityandplantpigments,(b)specificratesofETS,GDH,andATC Figure10:Comparisonofaveragetaxomomiccompositionofzooplankton>200µminMayand AugustinrelationtotheaverageN:PratiointheBalticSea(accordingtoPosteletal., 1992)     ETS GDH ATC EggProd Remi Respi Abundance Aspect BALTEX 05,1990OpenBaltic Sea, Pomeranian Bay xxxxxxx spring,summer, (autumn) Salinitygradient HELCOM 08,1990 x x x BALTEX 05,1991 x x x x x x BALTEX 08,1991 x x x x x x BALTEX 11,1991 x x x x x x BALTEX 05,1992 x x x x x x PLANKTON 08,1992xxx xxx PLANKTON 10,1993 Nearcoastal &openBaltic Sea xxxxxxx PLANKTON 09,1995 x x x x x x x PLANKTON 04,1996 x x x x x x x STORE‐ FJORD 06,1993 Norway x x x x x x x Verticalprofile to400(?)m Annual coastal Station 1999 2000 Warne‐ münde, RugenIsland xxx xxx Seasonalcycle, weeklysampling TRUMP 09,1993 Nearcoastal (Pomeranian Bay) xxx xxx Salinitygradient TRUMP 06,1994 x x x x x x TRUMP 01,1995 x x x x x x TRUMP 04,1995 x x x x x x TRUMP 07,1995 x x x x x x TRUMP 09,1995 x x x x x x TRUMP 10,1995 x x x x x x TRUMP 09,1993 x x x x x x ABFZ97 1997 ABFZ x x x x x x Frontalzone, Zonation ABFZ2000 (M48‐3) 2000 ABFZ x x x x Indik 1995 Meridional section xxx xxx Openocean ATLEX89 1989 Latitudional section xxx xxx Openocean  Table1:Reviewonzooplanktondatacollection(Project,when,where,parametermeasured,related aspects)  STOREFJORD93 BALTEX90‐92 PLANKTON92‐95 TRUMP ABFZ97,2000 INDIAN OCEAN95 ATLEX89 Figure1: Locationsofzooplanktonstudiesoncommunitystructure,metabolismandgrowthbyenzymaticand classicalmethodsbyLeibnizInstituteofBalticSeaResearch,Warnemünde,Germany,andpartlybyMarine ScienceFacultyoftheUniversityofLasPalmas,G.C.,Spain BALTEX90‐ 92 Figure2: SamplinglocationsintheBalticSeainMay1990 <100µm(BALTEX5_90) >100µm(Posteletal.1995) Inaverage:about6% Æsummer,whenmeso‐zooplanktonisabundant–upto38%! Primaryproductivityutilizedbyheterotrophs 25‐ 80% Figure7: Percentageofprimaryproductivityutilizedbyplankton<100µmandbyplankton>100µm Figure8: ComparisonofthecourseofinsituspecificETS‐ andGDHactivityofthefraction100to200µm betweenthewesternBalticSea(station12)andtheGulfofFinland(station305)andreturntoArkonaSea (station113)inMay,1990 lutz.postel@io‐warnemuende.de PomeranianBay, BalticSea,fall1993 Posteletal.(1995) Salinitygradient Eutrophicationgradient Figure9: CourseoftheinsituspecificmetabolicratesandgrowthoffthenOdraRivermouthinfall1993: (a)salinityandplantpigments lutz.postel@io‐warnemuende.de PomeranianBay, BalticSea,fall1993 Specificrespirationrate Specificgrowthrate Specificexcretionrate Figure9: Courseoftheinsituspecificmetabolicrates andgrowthoffthenOdraRivermouthinfall 1993:(b)specificratesofETS,GDH,andATC Cladocerans Parthenogenetic reproductionmode– highshorttermenergyrequirements(ATP) Copepods Averages1988,1990,1991,>200µm Stoichiometry innutrientrecycling N:PÆ6(inMay) N:PÆ10(inAugust) Figure10: Comparisonofaveragetaxomomic compositionofzooplankton>200µminMayandAugustinrelationto theaverageN:PratiointheBalticSea(accordingtoPostel etal.,1992)