Diel Vertical MigrationDiel Vertical Migration

Why Did Vertical Migration Why Did Vertical Migration Evolve?Evolve?1.1. Seek Optimal light intensity but why??Seek Optimal light intensity but why??

2.2. Avoid visual predatorsAvoid visual predators

3.3. Utilization of different water masses Utilization of different water masses (Hardy 1956)(Hardy 1956)

4.4. Energy conservation (McLaren 1963)Energy conservation (McLaren 1963)

5.5. Optimization of food (Enright 1977)Optimization of food (Enright 1977)

6.6. Ladder of migration (larger plankton Ladder of migration (larger plankton and nekton)and nekton)

Nutrients Nutrients PP PP ZP ZPFishFish

Bottom upBottom up

Top downTop down

Heterogeneity basisHeterogeneity basis

Density-dependent feedingDensity-dependent feeding

Assimilation efficiencyAssimilation efficiency

% assimilated = ingested – waste

ingested

pp concentration

% a

ssim

ilate

d

Is zooplankton mortality food-Is zooplankton mortality food-dependent?dependent?

Lag time and positive feedback loopsLag time and positive feedback loops

Nutrients Nutrients PP PP ZP ZPFishFishCritical factors affecting phytoplankton Critical factors affecting phytoplankton production-PS, growth rates, production-PS, growth rates, maintenance of biomass maintenance of biomass

Bottom up - nutrient and light limitsBottom up - nutrient and light limits

Top down – predation, competitoinTop down – predation, competitoin

Ocean ecosystem – classic Ocean ecosystem – classic model - model -

• PS – phytoplankton production- PS – phytoplankton production- copepods – predators – detrituscopepods – predators – detritus

• Pacific – tightly coupled – copepods Pacific – tightly coupled – copepods graze most of plankton, production graze most of plankton, production and energy in pelagic fishand energy in pelagic fish

• Atlantic, loosely coupled, production Atlantic, loosely coupled, production and energy in benthic fish via debrisand energy in benthic fish via debris

Ultra and Nanoplankton < 30 Ultra and Nanoplankton < 30 microns, microns, Bacterioplankton, flagellates, Bacterioplankton, flagellates, cocolithscocoliths

Diatoms, dinoflagellate driven model Diatoms, dinoflagellate driven model still holds for upwelling, coastal waters. still holds for upwelling, coastal waters. Why is this recent?Why is this recent?

Can account for 75% biomass, 80% Can account for 75% biomass, 80% production in epipelagic oceanic zoneproduction in epipelagic oceanic zone

Production & population size not Production & population size not seasonally variable. Esp tropics, gyres – seasonally variable. Esp tropics, gyres – why there ?why there ?

Advantage to small size? Advantage to small size?

Low nutrients & >s/v, < needs, protist Low nutrients & >s/v, < needs, protist symbionts in larger planktonic protozoasymbionts in larger planktonic protozoa

BacterioplanktonBacterioplankton• DOC huge reservoir, stable DOC huge reservoir, stable

• But ~ ¼ of PS fixed C is “leaked” as DOM - ??cont. But ~ ¼ of PS fixed C is “leaked” as DOM - ??cont. production of C vs stable amt? Where does it go? production of C vs stable amt? Where does it go? Why not build up?Why not build up?

• Up to 50% of total ocean production via direct Up to 50% of total ocean production via direct bacterial uptake (bacterial uptake (DOM + particles living and dead)DOM + particles living and dead)

• Bacterioplankton ext. abundant ~ 0.4 micron Bacterioplankton ext. abundant ~ 0.4 micron

• ““lost” production really recycled via bacteria into lost” production really recycled via bacteria into food chain food chain

• refractory DOM – humic acids, ligninsrefractory DOM – humic acids, lignins

• Dynamic DOM – amino acids, sugars, vitaminsDynamic DOM – amino acids, sugars, vitamins– High turnover; used by auxotrophs, heterotrophsHigh turnover; used by auxotrophs, heterotrophs

Nano food webNano food web– Macro phyto production – DOM by leakage and Macro phyto production – DOM by leakage and

lysis, plus photosynthesis, drives nano loop – lysis, plus photosynthesis, drives nano loop – regenerates/creates nutrientsregenerates/creates nutrients

– Bacterioplankton < 1 micron = 90% DOM Bacterioplankton < 1 micron = 90% DOM uptake, 60-65% assimilation efficiencyuptake, 60-65% assimilation efficiency

– High efficiency = convert DOM into POCHigh efficiency = convert DOM into POC

– Nano biomass>> macro phyto plankton Nano biomass>> macro phyto plankton

– Predators - ciliates, non-photo flagellatesPredators - ciliates, non-photo flagellates

– Consume most nanoplankton production, Consume most nanoplankton production, consumed by macro planktonconsumed by macro plankton

Sources of DOMSources of DOM

1.1. PP cells are inherently “leakyPP cells are inherently “leaky- normal, healthy cells exude 1-20% of fixed - normal, healthy cells exude 1-20% of fixed carboncarbon

- senescent cells even more leaky- senescent cells even more leaky

2.2. Autolysis +/or bursting of old, injured, Autolysis +/or bursting of old, injured, virus-infected cellsvirus-infected cells

3.3. Exudates to serve functional need of cellExudates to serve functional need of cell- auxotrophs to attract vitamin-producers- auxotrophs to attract vitamin-producers

- competitive interference- competitive interference

- water conditioners- water conditioners

Sources of DOMSources of DOM

4.4. Loss during ingestionLoss during ingestion

- zp sloppy eaters, especially high - zp sloppy eaters, especially high grazing rate areasgrazing rate areas

5.5. ExcretionExcretion

- - about 10% of C ingestedabout 10% of C ingested

Bacteria regenerate nutrients in low nutrient Bacteria regenerate nutrients in low nutrient waterswaters

DOM UtilizationDOM Utilization

• Direct – primarily bacteria, but some Direct – primarily bacteria, but some zooplanktonzooplankton

• Indirect – extra links in ignored food Indirect – extra links in ignored food chainchain

““microbial loop”microbial loop”

100

60

6

0.6

0.06

Marine snow – organic Marine snow – organic aggregatesaggregates

• Air bubbles breakingAir bubbles breaking

• Adsorption to silt particles, salt crystalsAdsorption to silt particles, salt crystals

• Cast off molt skins, mucus nets, fecal Cast off molt skins, mucus nets, fecal pellets, etc.pellets, etc.

Intense sites of bacterial decomposition, Intense sites of bacterial decomposition, nutrient recyclingnutrient recycling

Paradox of the Plankton – Paradox of the Plankton –

TTee = time between environmental changes = time between environmental changes

TTcc = time to competitive exclusion = time to competitive exclusion

TTcc < T < Tee T Tcc > T > Tee TTcc ~~ T Tee

how can so many species coexist in a how can so many species coexist in a seemingly homogeneous ocean?seemingly homogeneous ocean?

Are the Are the Oceans Oceans HomogeneouHomogeneous?s?

Small-scale patchinessSmall-scale patchiness– Marine snowMarine snow– MicroturbulenceMicroturbulence– Vertical differences in light, other Vertical differences in light, other

factorsfactors

Moderate-scale patchinessModerate-scale patchiness– Coastal frontsCoastal fronts– Langmuir circulationLangmuir circulation– Ocean eddies or ringsOcean eddies or rings

Large-scale patchinessLarge-scale patchiness– Major continental upwelling zonesMajor continental upwelling zones– Equatorial upwelling zonesEquatorial upwelling zones– Current convergence zoneCurrent convergence zone– Major ocean gyre systemsMajor ocean gyre systems

Biological Interactions (top down)Biological Interactions (top down)– GrazingGrazing– Variations in reproductive rateVariations in reproductive rate– Social behaviorSocial behavior– Interspecific interactions that attract or Interspecific interactions that attract or

repulserepulse