Diel Vertical Migration

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Diel Vertical Migration
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Why Did Vertical Migration Evolve?

1. Seek Optimal light intensity but why??
2. Avoid visual predators
3. Utilization of different water masses (Hardy
   1956)
4. Energy conservation (McLaren 1963)
5. Optimization of food (Enright 1977)
6. Ladder of migration (larger plankton and nekton)

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Heterogeneity basis
Nutrients PP ZP Fish
Bottom up Top down
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Density-dependent feeding
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Assimilation efficiency assimilated
ingested waste ingested
assimilated
pp concentration ?
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Is zooplankton mortality food-dependent?
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Lag time and positive feedback loops
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Nutrients PP ZP Fish
Critical factors affecting phytoplankton
production-PS, growth rates, maintenance of
biomass Bottom up - nutrient and light
limits Top down predation, competitoin
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Ocean ecosystem classic model -

• PS phytoplankton production- copepods
  predators detritus
• Pacific tightly coupled copepods graze most
  of plankton, production and energy in pelagic
  fish
• Atlantic, loosely coupled, production and energy
  in benthic fish via debris

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Ultra and Nanoplankton lt 30 microns,
Bacterioplankton, flagellates, cocoliths Diatoms,
dinoflagellate driven model still holds for
upwelling, coastal waters. Why is this
recent? Can account for 75 biomass, 80
production in epipelagic oceanic zone Production
population size not seasonally variable. Esp
tropics, gyres why there ? Advantage to small
size? Low nutrients gts/v, lt needs, protist
symbionts in larger planktonic protozoa
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Bacterioplankton

• DOC huge reservoir, stable
• But ¼ of PS fixed C is leaked as DOM -
  ??cont. production of C vs stable amt? Where does
  it go? Why not build up?
• Up to 50 of total ocean production via direct
  bacterial uptake (DOM particles living and
  dead)
• Bacterioplankton ext. abundant 0.4 micron
• lost production really recycled via bacteria
  into food chain
• refractory DOM humic acids, lignins
• Dynamic DOM amino acids, sugars, vitamins
• High turnover used by auxotrophs, heterotrophs

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Nano food web

• Macro phyto production DOM by leakage and
  lysis, plus photosynthesis, drives nano loop
  regenerates/creates nutrients
• Bacterioplankton lt 1 micron 90 DOM uptake,
  60-65 assimilation efficiency
• High efficiency convert DOM into POC
• Nano biomassgtgt macro phyto plankton
• Predators - ciliates, non-photo flagellates
• Consume most nanoplankton production, consumed by
  macro plankton

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Sources of DOM

• PP cells are inherently leaky
• - normal, healthy cells exude 1-20 of fixed
  carbon
• - senescent cells even more leaky
• Autolysis /or bursting of old, injured,
  virus-infected cells
• Exudates to serve functional need of cell
• - auxotrophs to attract vitamin-producers
• - competitive interference
• - water conditioners

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Sources of DOM

• Loss during ingestion
• - zp sloppy eaters, especially high grazing rate
  areas
• Excretion
• - about 10 of C ingested
• Bacteria regenerate nutrients in low nutrient
  waters

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DOM Utilization

• Direct primarily bacteria, but some zooplankton
• Indirect extra links in ignored food chain
• microbial loop

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0.06
0.6
6
60
100
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Marine snow organic aggregates

• Air bubbles breaking
• Adsorption to silt particles, salt crystals
• Cast off molt skins, mucus nets, fecal pellets,
  etc.
• Intense sites of bacterial decomposition,
  nutrient recycling

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Paradox of the Plankton
how can so many species coexist in a seemingly
homogeneous ocean?

• Te time between environmental changes
• Tc time to competitive exclusion
• Tc lt Te Tc gt Te Tc Te

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Are the Oceans Homogeneous?
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• Small-scale patchiness
• Marine snow
• Microturbulence
• Vertical differences in light, other factors
• Moderate-scale patchiness
• Coastal fronts
• Langmuir circulation
• Ocean eddies or rings

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• Large-scale patchiness
• Major continental upwelling zones
• Equatorial upwelling zones
• Current convergence zone
• Major ocean gyre systems

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• Biological Interactions (top down)
• Grazing
• Variations in reproductive rate
• Social behavior
• Interspecific interactions that attract or repulse