Accountingforgrazingdynamicsinnitrogen-phytop

1、Accountingforgrazingdynamicsinnitrogen-phytopLimnol.Oceanogr.,52(2),2021,649661E2021,bytheAmericanSocietyofLimnologyandOceanography,Inc.Accountingforgrazingdynamicsinnitrogen-phytoplankton-zooplanktonmodelsAditeeMitraandKevinJ.Flynn1InstituteofEnvironmentalSustainability,UniversityofWalesSwansea,Sin

2、gletonPark,SwanseaSA28PP,UnitedKingdomMichaelJ.R.FashamNationalOceanographyCentre,SouthamptonSO141ZH,UnitedKingdomAbstractNitrogen-phytoplankton-zooplankton(NPZ)typemodelsarewidelyusedtoexplorethedynamicsofmarineplanktonicecosystems.Withinthesemodels,grazingbyzooplanktononphytoplanktonthataresubject

3、edtovaryingdegreesofnitrogenlimitationisdescribedusingN-basedgrazingkineticstogetherwithfixedNassimilationefficiency.Thereisnoempiricalevidenceforzooplanktondisplayingsuchbehavior;onthecontrary,thereisevidenceforadeclineinzooplanktongrowthratesonconsumptionofN-impoverishedprey,withdecreasedassimilat

4、ionefficienciescoupledwithdecreasedingestionratesofnutrient-limited(.,poorquality,lowN:C)prey.Unwittingly,then,traditionalNPZmodelsmakeunjustifiedassumptionsconcerningchangesinpredatorpreyinteractionsonconsumptionoflow-qualityprey.Weexploretheeffectsofthisflaweddescription,alsoaskingwhyNPZmodelscans

5、tillgivereasonabledescriptionsoffielddata.Ourconclusionisthatoneflawmaybecounteredbyanother,namely,byaninadequatedescriptionofnongrazingphytoplanktonlosses.Innature,thesenongrazinglossesareenhancedwithinnutrient-depletedphytoplanktonpopulations.Inmodels,adeclineingrazinglossesonnutrient-deprivedphyt

6、oplanktonis,defacto,pensatedforbyenhancednongrazinglosses.Whilethefitoftherevisedmodeltothedataisnotdissimilartothatoftheoriginalmodel(withitsinappropriatedescriptionsofgrazingandnongrazingphytoplanktonmortality),thefateofprimaryproductionisverydifferent.Withthebiologicallymoreacceptabledescription,

7、morematerialflowsthroughthedetritalpartment,withimportantimplicationsfortrophicdynamics.Caremustbetakennottooversimplifydescriptionsofbiologyinmodels,asthesemaydirectlyorindirectlymaskthesimulationofotherimportantecologicalprocesses.Overthepastdecadetherehasbeenaconcertedefforttoincreasetherealismof

8、ecosystemmodelsthatdescribeplanktonproduction.Mostofthisefforthasbeenexpendedonthedescriptionofphytoplankton;thus,multinutrient,photoacclimationmodelsarenownotunmon(.,Fashametal.2021).Zooplanktongrazingfunctionshavebeenshowntobeimportantdeterminantsforplanktonsystemdynamics(Steele1976;SteeleandHende

9、rson1992;StromandLoukos1998;MitraandFlynn2021).Thus,itisjustasimportanttojustifytheconstructionofzooplanktonmodelsforincorporationwithinecosystemmodelsasitistodosoforphytoplanktonmodels(Flynn2021,2021b).However,thedescriptionofzooplanktonmodelshaschangedlittle,otherthanbytheinclusionofmorezooplankto

10、ngroups(micro-,mesozooplanktonandsoon;.,Blackfordetal.2021)andbythegreaterappreciationoftheimportanceofstoichiometry(.,carbon:nitrogen:phosphorusC:N:P)inaffectingassimilationandhencegrossgrowthefficiencyofthezooplanktonpredator(.,SternerandElser2021;Andersonetal.2021).Thesezooplanktonmodelsdonotcons

11、idertheeffectsofpreyqualityandavailabilityonpreyselection,ingestionkinetics,andgrowthdynamics.1Correspondingauthor(.flynn.uk).AcknowledgmentsThisworkwassupportedbytheNaturalEnvironmentResearchCouncil(UnitedKingdom).Wegratefullyacknowledgereviewmentsonpreviousversionsofthiswork.Recently,wehavedevelop

12、edmodelstoenableaconsiderationoftheeffectsofpreyofdifferentqualityandquantityonzooplanktoningestionandgrowthkinetics(Mitra2021;MitraandFlynn2021a,2021b).Thesefactorsareimportantbecausechangesinphytoplanktonnutrientstatus,typicallyassociatedwithnutrientexhaustionandoftenwiththeaccumulationoftoxins(Ce

13、mbella2021),canstimulatechangesinzooplanktonpredationbehavior(Irigoienetal.2021;MitraandFlynn2021).Suchchangesinbehavior,associatedwithstoichiometricdisparitybetweenpredatorandprey,havebeentermedstoichiometricmodulationofpredation(SMP;MitraandFlynn2021).InthispaperweconsidertheimplicationsofSMPfortheperformanceofwhatcanprobablybeconsideredtheclassicmodelingdescriptionofmarineplanktonicecosystems,namely,thenitrogen-phytoplankton-zooplankton(NPZ)model(Fashametal.1990;Evans