Plankton Food Webs

8/2/2019 Plankton Food Webs

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• Someplankton,suchasdiatoms,growbetteratcoolertemperatures.Warmingmaycauseother,lesspalatable,speciestoreplacethem,deprivingzooplanktonandmenhadenoftheirprimaryfoodsource.

• Becausephytoplanktonarelinkedtofreshwaterandnutrientinputs,draughtwilllikelydecreasetheirabundance.Also,whennutrientsarereduced,smallerphyto -

planktonreplacediatoms,andthealteredsizeimpactstheentirefoodweb.Changesinprecipitationwillhaveamajorimpactonestuarineplankton.

• Increasesincarbondioxide(CO2)affect

thegrowthofcertainspecies,butnotall

speciesareimpactedthesame.1Somealgae,suchasCyanobacteria,arefavoredunderhighertemperaturesandCO

2

concentrations.Cyanobacteriacanformnoxiousblooms(seeFigure2);therefore,CO

2changeswilllikelycreatechangesin

thecompositionofplankton,whichwillcascadethroughoutthefoodweb.

Likely impacts of climate change on plankton in estuaries andcoastal systems:

Marine Plankton Food Websand Climate Change

Plankton Food Webs

Estuarineandcoastalmarinefoodwebsaredominatedbyplankton–organismsthatdriftwiththecurrents.Composedofphytoplankton–photo-syntheticmicroscopicalgae;zooplank-ton–animalsthateatphytoplanktonoreachother;andbacterioplankton–microbesthatdegradeorganicmat-

ter,planktonexistinanever-chang-ingaquaticenvironmentthatrequiresthemtorespondquicklytochangesintheirhabitat–onthetimescalesofdaystoweeks.Theplanktonarethusoftenthefirsttobeimpactedbyclimatechange.

Harmful Algal Blooms

Manytypesofphytoplanktoncangrowandreachhighnumberswhennu-

trients(nitrogen(N)andphosphorus(P))areaddedbyhumanactivities.Whenthishappens,itistermeda“harmfulalgalbloom”orHAB.HABsoftenhavehighconcentrationsoftoxiccompoundsthatcanaccu-mulateinorkillfilterfeedingorganisms.Ifpeopleeatthefilterfeeders(forexample,oysters),illnessordeathcanresult.HABshaveoccuredthroughouthistory,buttheirnumbersandfrequencyhavegreatlyincreasedinthepast30years,mostlikelyduetohigherNandPloadstocoastalwaters.2HABshavebeennotedinupperChesa-peakewatersforsometime3(Figures2,3onnextpage),andrecentlyhaveoccurredinthelowerChesapeakeaswell.TheeconomicimpactsofHABsaresubstantial;theAlexandriumbloominNewEnglandin2003wasestimatedtocosttheregionca.$50

million,andasimilarfigurewasestimatedforthePfisteriaoutbreakinChesapeakeBayin1997.AnnuallyHABscauseapproximately$40millioninreductionsinfisheriesandshellfishharvestsanddeclinesintouristactivities,andthisnumberwillverylikelyincreaseinthefuture.Allofthesechangesinphytoplanktonresultinchangesinbothzoo-andbacterioplankton.EffectsofHABsonthefoodwebcanbemitigatedbyzoo-planktongrazers,whichhavevaryingsusceptibilitytoHABtoxins.4Furthermore,HABspecies,byvirtueoftheirhighabundance,oftenseverelyreducetheoxygenpresentinthewateratnight,andcausephysiologicaldamagetootherspecies.

Figure 1. Example of a plankton food web.

Zooplankton and fsh

A dinoflagellate, a type of phytoplankton thatforms harmful algal blooms.



Climate shifts will change not only the abundance and growthrates of species in estuarine and coastal environments, but

likely result in a shift in the type of species present, withunknown consequences to the food web.

Changes in Jellyfish

Anotherexampleofclimateandhuman-inducedshiftsinfoodwebsisthelargeincreaseinjellyfishpopulationsthathaveoccurredincoastalandestuarineeco-systemsworldwide.5Theincreasemaybeinresponsetoincreasesinnutrientsthatstimulatephytoplankton,whichinturnstimulateotherzooplanktonsuchascope-pods(themajorfoodsourceofjellyfish).Analternateexplanationisthatoverfish-ingdecreasesplankton-eatingfishpopulations,thejellyfish’smajorcompetitorfor

food,allowingjellyfishtoincreaseinnumbers.AstrikingseasonalchangeinthezooplanktonofChesapeakeBayistheincreasedabundanceofjellyfishinsummermonths,suchasseanettlesandcombjellies(Figure4).Seanettlesareaspeciesofjellyfishthatstingshumans,causingapainfulirritationthatcanonlybepartiallytreated.Otherformssuchascombjelliesdonotsting,butalsocompeteforfoodagainstcommerciallyimportantfish.DuetotemperatureincreasesinChesapeakeBay,combjelliesaredevelopingone-monthearlierthantheydid40yearsago,withunknownconsequencesforthefoodweb(Figure5).6Giventhatbothseanettlesandcombjelliesarevoraciouseaters,itisexpectedthatthecopepodstheyfeedonwillbegreatlyreducedinnumbersthusstressingotheranimals,suchasBayanchovyorstripedbass,thatdependoncopepodsforfood.

Changes in Bacterioplankton

Bacterioplanktonchangeaswell,althoughtheirfunctionalrolesarelikelytoremainsimilar,eveniftheirstandingstocksincrease(whichalsoresultsinanincreasedoxy -

gendemandwithinthewatercolumn).Lomassuggestedthatchangesinbacterialabundancewillbesubstantiallylargerthanthoseofphytoplanktonunderconditionsoffuturetemperatureincreases.7Thetypesofbacteriapresentmayalsochange,andcertainhumanpathogensmightflourishrelativetootherbacterioplankton,therebyimpactinghumanuseoftheestuary.

Changes in Timing of Natural Cycles

Climatechangeisalsolikelytoalterthetimingofnaturalevents.Asmentionedpreviously,diatomsoftenbloominwinterwhentemperaturesarelow.Zooplank-ton,becausetheirlifehistoryiscontrolledbytemperature,oftenlagbehindthephytoplankton.Thistimedelaystructurestheestuaryandcoastalsystem,provid-ingenergytobottom-dwellingcommunitiesthroughthesinkingofdeadphyto-plankton.Astemperaturesincrease,zooplanktonreproductiverateswillincrease,reducingthedelaybetweenphyto-andzooplanktonblooms.Ifphytoplanktonbecomemoretightly“coupled”tozooplankton,inputstothebenthosmaybealtered,modifyingenergyflowwithinestuarineandcoastalfoodwebs.

Figure 2. Distribution of harmful algal blooms on theeast coast of the U.S. The orange area representsblooms of Pfisteriaand Karlodinium; green areascyanobacterial blooms; brown areas brown tides. Hu-man health impacts from paralytic shelf fish poisoning(red) and Pfisteria have occurred in the past 10 years.Based on http:/ / www.whoi.edu/ redtide/ page.do?pid=9257.

Figure 3. A harmf ul algal bloom (HAB) in the Eliza-beth River, Chesapeake Bay. Photo by L. Kill berg.



Summary of Climate Impacts on Coastal Plankton

Inthenearfuture,changesinenvironmentalvariablessuchasnutrients,tempera-ture,salinity,andCO

2concentrationscanbeexpectedto

• Changenotonlytheabundanceandgrowthratesofplanktonspeciesinestua-rineandcoastalenvironments,butlikelyresultinashiftinthetypeofspeciespresent,withunknownconsequencestothefoodweb;

• Produceinteractiveeffectsresultinginperturbationsthatfarexceedchangesinonevariable;

• Increasethegrowthandaccumulationofnoxiousspecies(suchasharmfulalgaeandjellyfish),withsevereattendantsocioeconomicandhumanhealthimpacts;

• Alterthetimingofnaturalevents,withsignificantimpactsonestuarineandcoastalfoodwebs.

• Economicallyimportantspecieswillbeinfluenceddirectlybyclimate-inducedchangesinplankton.

Key Future Climate Change Issues: Plankton

Whilemanyoftheimpactsofclimatechangeonestuarineandcoastalplanktonarebroadlyknown,fartoolittleisknownconcerningthespecificmechanismsofhow

thesechangeswilloccur.Fourmajorquestionsneedtobeaddressedbyfocused

Figure 4. A sea nett le (Chrysaoraquinquecirrha), aspecies of zooplankton that forms large accumula-tions in Chesapeake Bay. They become ext remelyabundant and grow rapidly when water temperaturesexceed 25ºC. They are noxious in that they sting and

are harmful to humans. There is no effective meansto reduce their abundance. From http:/ / www.bbep.org/

jellyf ish.html

Figure 5. Blooms of comb jell ies (the ctenophore Mnemiopsisleidyi,shown in insert) arepresently occurring one month earlier than they did 40 yrs. ago, most l ikely due to risingseawater temperature which allows ctenophores to reproduce earlier. Comb jell ies consumezooplankton, thus could potentially deprive fish of f ood. From Condon and Steinberg, in press.

Figure 6. Marine bacteria cells (small glowing dots)which are 1/ 1000 mm in size. A small flagellate(larger cell with flagella) animal that feeds on bacte-rioplankton is also shown. Photo by C. Carlson.



Prepared By:Walker Smith

Deborah SteinbergDeborah Bronk

Kam Tang

Virginia Institute of Marine Science

References Cited

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Phone: (804) 684-7000 Printed on recycled paper. October 2008

1 Hutchins,D.A.,F.-X.Fu,Y.Zhang,M.E.Warner,Y.Feng,K.Portune,P.W.Bernhardt,andM.R.Mulholland.2007.CO

2controlofTrichodesmiumN

2fixation,photosynthe-

sis,growthrates,andelementalratios:Implicationsforpast,present,andfutureoceanbiogeochemistry.Limnology and Oceanography,52(4),1293-1304.

2 Anderson,D.M.,P.M.Glibert,andJ.M.Burkholder.2002.Harmfulalgalbloomsandeutrophication:nutrientsources,composition,andconsequences.Estuaries,24,704-726.

3 Glibert,P.M.,R.Mangian,M.W.Lomas,J.Alexander,C.Fan,E.Haramoto,M.Trice,andT.Kana.2001.Harm-fulalgalbloomsintheChesapeakeandcoastalbaysofMaryland,USA:Comparisonof1997,1998and1999events.Estuaries,24,875-883.

4 Colin,S.P.,andH.G.Dam.2002.Latitudinaldifferentia-tionintheeffectsofthetoxicdinoflagellateAlexandriumspp.onthefeedingandreproductionofpopulationsofthecopepodAcart ia hudsonica.Harmful Algae,1,113-125.

5 Purcell,J.E.2005.Climateeffectsonformationofjel-lyfishandctenophoreblooms:Areview.Journal of theMarine Biological Association of the United Kingdom,85,461-476.

6 Condon,R.H.,andD.K.Steinberg(inpress).Develop-ment,biologicalregulation,andfateofctenophore(Mnemiopsis leidyi)bloomsintheYorkRiverestuary,USA.Marine Ecology Progress Series.

7 Lomas,M.W.,P.W.Glibert,F.-K.Shiah,andE.M.Smith.2002.MicrobialprocessesandtemperatureinChesa-peakeBay:Currentrelationshipsandpotentialimpactsofregionalwarming.Global Change Biology,8,51-70.

researchinordertoaidtheCommonwealthinitsgoalstounderstand,mitigate,andpredicttheimpactsofclimatechangeinitswaters:

1. Whataretheeffectsofalteredenvironmentalregimesinthecontrolofphytoplank-tongrowthandaccumulation?

2. Willclimatechangeinducelarger,moreextensive,andmoredamagingHABs,andifso,whataretheproximalcauses?

3. Howwillclimaticallyalteredenvironmentalparameters(nutrient,salinity,CO2)and

changesinphytoplanktonaffectzooplanktonreproductionandcomposition?

4. Whateffectsdoclimate-inducedchangesintheplanktonhaveonhighertrophiclevelsandcommerciallyimportantfish?

Likely Social and Economic Consequences

ClimatechangewillbringtotheCommonwealthassociatedcosts,someofwhichcanbepredicted,butotherswhichatthistimecannot.Itispredictablewithalargedegree

ofcertaintythattemperatureandenvironmental(nutrient,salinity,CO2)changeswillresultinanalteredplanktoncommunity,andthatthischangewilllikelydegradethesocioeconomic“return”fromtheestuaryandcoastbydecreasingyieldofharvestablespeciesandalteringthehumanlifestylesdependentonthose.ItisalsoprobablethatHABswillincreaseinmagnitude,duration,anddistribution,andthattherewillbeasubstantial,negativeeconomicimpactontheCommonwealth.Althougheconomicmodelshavenotassessedthisloss,itcanbeexpectedthatitwillannuallybefrom$3-10milliondollarsperyearintermsoflostharvestsofcertainspecies.Lossoftourismviathegrowthofnoxiousorganisms(HABs,jellyfish)willalsobesignificant,especiallyifsuchbloomsbegintosignificantlyexpandintocoastalwaters.

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Plankton Food Webs