9 Critical Factors in Plankton Abundance
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Transcript of 9 Critical Factors in Plankton Abundance
9 Critical Factors in Plankton Abundance
Notes for Marine Biology: Function, Biodiversity,
EcologyBy Jeffrey S. Levinton
Spring Phytoplankton Increase(or Spring Diatom Increase)
In midlatitudes, phytoplankton increase inthe spring, decline in summer, and may increaseto a lesser extent in fall
Nutrientsat surface
SpringDiatomIncrease
Zooplankton
Availablesunlight
Winter Spring Summer Fall Winter
Arctic
Temperate
Tropical
Phytoplankton
Phytoplankton
Herbivorezooplankton
PhytoplanktonHerbivorezooplankton
J F M A M J J A S O N D
Month
Mechanisms causing the spring phytoplankton bloom and its
decline
Light and Phytoplankton - concepts
Compensation depth - that depth at whichoxygen produced by a phytoplankton cell inphotosynthesis equals the oxygen consumed inrespiration
Consider a phytoplankton cell held in jarat a certain depth ( = a certain light intensity:
Light and Phytoplankton - concepts 2
Compensation light intensity - the lightintensity corresponding to the compensationdepth
Consider a phytoplankton cell held in jarat a certain depth ( = a certain light intensity:
Before the spring phytoplankton increase:
Water density similar at all depthsWind mixing homogenizes water column
Cause of the spring phytoplankton increase:
Important concepts:
Mixing depth - depth above which all wateris thoroughly mixed, due to wind.
Critical depth - depth above which total oxygencoming from primary production in the water column equals total consumption (respiration)
If: Mixing depth < Critical depth: bloomIf: Mixing depth > Critical depth: no bloom
Total respiration, RTotal photosynthesis, P
Compensationdepth
Mixing depth 1
CriticalDepth
Mixing depth 2
Depth
Oxy
gen
pro
du
ctio
n (
P )
or
resp
irat
ion
( R
)
Mixing depth 1: area P > RMixing depth 2: area P < R
Cause of the spring phytoplankton increase:
Important concepts 2:
Key processes: 1. Water column becomesmore stable in spring as sun heats water from above. 2. Surface nutrients are rich and trapped in surface waters. 3. Phytoplankton cells are no longer stirredto darker deep waters ----> BLOOM!!
Decline of the Spring Phytoplankton Increase
Why do phytoplankton decline?Water column is STABLEIn shallow water shelf waters: diatoms startsinking from surface water to bottom,which removes nutrients.
Decline of the Spring Phytoplankton Increase 2
Why do phytoplankton decline?
Zooplankton grazing? Has some effect butoften secondary to sinking
Rejuvenation of conditions for the Spring Phytoplankton
Increase
Why do phytoplankton increase again in Fall?
In fall and winter: water cools, water columnbecomes isothermal with depth, wind mixingrestores nutrients to surface waters until conditions are right next spring
Water column exchange in shallow waters and estuaries
In very shallow estuaries, nutrient exchangeor benthic-pelagic coupling, occurs betweenthe bottom and the water column, fueling more phytoplankton growth
Water column exchange in shallow waters and estuaries 2
Beach phytoplankton blooms
Water column exchange in shallow waters and estuaries 3
In estuaries, the spring freshet combineswith net water flow to the sea and mixing todetermine nutrient regime:1. Freshwater rivers create a net downstream flow2. Tides cause mixing up and down estuary as well as vertical mixing3. Nutients may be released to coastal zone
Water column exchange in shallow waters and estuaries 4
Important factors in nutrient exchange:1. Residence time - time water remains in estuarybefore entering ocean2. Rate of nutrient input from watershed3. Nutients may be released to coastal zone
Light
Two components of loss in the waterColumn:
Absorption: Molecular absorptionof light energy
Scattering: Light interaction withparticles
Light 2
Penetration into water column varies:with wavelength
Clear Open Ocean Water: Maximumpenetration at 480 nm
Turbid inshore water: Maximumpenetration at 500-550 nm
Light 3
Ultraviolet light strongly attenuatedIn water column:
Inshore waters: Incident light with wlof 380 nm or less is almost attenuatedat depth of 1-2 mClear open ocean water: 20 m maybe required to remove 90% of surfaceincident light
Photosynthesis in Water Column
Phytoplankton species may useChlorophyll a, c and “accessory pigments”, which absorbenergy over the light spectrum
Photosynthesis in Water Column 2
Action spectrum - utilization ofdifferent wavelengths of light bya given species for photosynthesis
Chlorophyll absorbs wavelengths ofmainly > 600 nmAccessory pigments absorb wavelengths< 600 nm
Photosynthesis in Water Column 3
Photosynthesis increases with increasing light intensity to a plateau, Pmax, then decreases
Light intensity (I)
NetPhotosynthesis
Grossphotosynthesis
Respiration
Pmax
Pho
tosy
nthe
tic
rate
Compensation point+_0
Nutrients
Nutrients are substances required by plants.They are resources that can be limited in supplyNutrient dependence and use:Autotrophs, auxotrophs, heterotrophs
Nutrients 2Nitrogen - what for?Nitrates NO3 -Nitrites NO2 -Ammonium ion, NH4 - excretion product recycling from animal excretion in thewater column
Nutrients 3
Nitrogen - uptake depends upon source
Ammonium ion is taken up the fastestby phytoplankton cells, requires the leastchemical alteration (no reduction), but Nitrate is usually the most abundant sourceOf nitrogen in shallow coastal water columns
Nutrients 4
Nitrogen - New vs. Regenerated ProductionNew Production:Nutrients for primary production may Derive from circulation of nutrients fromBelow the surface waters (upwelling, stormsThat bring deeper waters to the surface)Regenerated Production:Nutrients derive from recycling in surfacewaters from excretion
Nutrients 5Nitrogen - Microbial control
Nitrogen added to ocean from atmospheric nitrogen by nitrogen fixing bacteriaNitrifying bacteria convert NH4 to NO2, others convert NO2 to NO3
Denitrifying bacteria convert N03 to NH4
Nitrate reducing bacteria return NO3 to atmosphere
Atmospheric nitrogen
Denitrification Nitrogen fixation
Primary production
Respiration
Dissolvedinorganicnitrogen
Organicnitrogen
Advection,Mixing
External nitrogensources and sinks
Nitrogen Cycle
Nutrients 6Phosphorus - occurs dissolved in water mainly as phosphate PO4
Also can find particulate phosphorus,some dissolved P in organic molecules
Phosphorus required for synthesis of ATP, source of energy of cellular reactions
Primary productionDissolvedInorganic
phosphorus
Organicphosphorus
External phosphorussources and sinks
Advection andmixing
Respiration
Phosphorus Cycle
Nutrients 7The limiting nutrient? In ocean,nitrogen is believed to be the mainelement limiting phytoplankton growth, Rather than phosphorus
Important question are these the only limitingnutrients or nutrient elements?
Nutrients 8Silicon - important limiting elementfor diatoms, exact role in controllingphytoplankton growth not well understood
Nutrients 9Iron - important cofactor in oxygenproduction step of photosynthesis
Shown in lab experiment to enhance phytoplankton growth
May be crucial in parts of the ocean (easternequatorial Pacific, parts of Antarctic, northPacific where nitrogen appears not to belimiting factor
Nutrients 10Trace elements such as Mn, Zn, Mo,Co, Cu can be important, but poorly understood
Organic trace substances such as vitaminsimportant, especially for auxotrophic phytoplankton (e.g., many dinoflagellates)
Phytoplankton Succession
Seasonal change in dominance bydifferent phytoplankton speciese.g.: diatoms in early spring followedby dinoflagellates in summer
Phytoplankton Succession 2
Mechanisms poorly understood:
1. Shift in advantage of nutrient uptake,Favoring different cell types2. Species later in season may depend uponsubstances that are not in the water columnin early spring (e.g., auxotrophic species mightfollow autotrophic species)
Microbial Loop1. Bacteria are abundant and take up largeAmounts of nutrients from the water column
2. Bacteria are consumed by ciliates and otherHeterotrophs
3. These heterotrophs are consumed by otherSmaller zooplankton, which incorporates Bacterially derived nutrients into the planktonicFood web
Microbial Loop 2
Microbial loopDOC & POC
Viruses
Bacteria
Microconsumers
DIOC andnutrients
Phytoplankton
Herbivores
Larger consumers
DOC=dissolved organic carbonPOC=particulate organic carbonDIOC=dissolved inorganic carbon
Nutrient uptakeNutrient uptake by phytoplankton cellsvaries with nutrient concentration
Modelling uptake:Need to know (1) nutrient concentration CAnd (2) rate of uptake of nutrients, which we measure indirectly as D, cell doublings/day(3) K is concentration at which cell doublingrate is one half of maximum doubling
Nutrient uptake 2
K
Dmax
Dmax/2
Nutrient concentration
Cel
l dou
blin
gs/d
ay
Nutrient uptake 3
K
K is nutrient concentration at whichhalf of maximum cell doubling rateoccurs - useful measure of phytoplanktonNutrient uptake
Nutrient concentration
Cel
l dou
blin
g ra
te
Nutrient uptake 4
Application of model: Inshore versus open ocean phytoplankton nutrient uptake
Inshore species: live in higher nutrientconcentrations, should be good at uptake at highconcentrations, but may be tradeoff and lowerefficiency at low nutrient concentrations
Nutrient uptake 5
Application of model: Inshore versus open ocean phytoplankton nutrient uptake 2
Open ocean species: live in lower nutrient concentrations, should be better at uptake at lowerconcentrations but tradeoff is inability to dealwith higher concentrations.
Nutrient uptake 6
Application of model: Inshore versus open ocean phytoplankton nutrient uptake
Dmax-1
Dmax-2
K2 K1
1
2
Adapted to highnutrient concentrationAdapted to lownutrient concentration
Nutrient uptake 7
General results for nitrate:
Dmax-1Dmax-2
K2 K1
Adapted to highnutrient concentrationAdapted to lownutrient concentration
Environment K
Inshore 1M
Offshore 0.1-0.2 M
Zooplankton Grazing
Grazing effect: Difference between grazingrate and phytoplankton growth rate
Grazing quite variable, sometimes causes:1. Strong spatial variation in phytoplanktonabundance,2. Cycles of phytoplankton abundanceand decline
Zooplankton Feeding
Zooplankton feeding increases with increasing phytoplankton cell density, up to a plateau
Phytoplankton cell density
Cel
l ing
esti
on r
ate
Copepod feeding response on a diatom
The End