Transcript 5 Plankton and Spatial patterns jh

Diel Vertical Migration
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)
Heterogeneity basis
Nutrients
Bottom up
Top down
PP
ZP
Fish
Density-dependent feeding
Assimilation efficiency
% assimilated = ingested – waste
% assimilated
ingested
pp concentration 
Is zooplankton mortality food-dependent?
Lag time and positive feedback loops
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
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
Ultra and Nanoplankton < 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 & >s/v, < needs, protist
symbionts in larger planktonic protozoa
Bacterioplankton
• DOC huge reservoir, stable
• But ~ ¼ of PS fixed C is “leaked” as DOM •
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??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,
Nano food web
– Macro phyto production – DOM by leakage
and lysis, plus photosynthesis, drives nano
loop – regenerates/creates nutrients
– Bacterioplankton < 1 micron = 90% DOM
uptake, 60-65% assimilation efficiency
– High efficiency = convert DOM into POC
– Nano biomass>> macro phyto plankton
– Predators - ciliates, non-photo flagellates
– Consume most nanoplankton production,
consumed by macro plankton
Sources of DOM
1. PP cells are inherently “leaky
- normal, healthy cells exude 1-20% of fixed carbon
- senescent cells even more leaky
2. Autolysis +/or bursting of old, injured, virus3.
infected cells
Exudates to serve functional need of cell
- auxotrophs to attract vitamin-producers
- competitive interference
- water conditioners
Sources of DOM
4. Loss during ingestion
- zp sloppy eaters, especially high grazing rate
areas
5. Excretion
- about 10% of C ingested
Bacteria regenerate nutrients in low nutrient
waters
DOM Utilization
• Direct – primarily bacteria, but some
zooplankton
• Indirect – extra links in ignored food chain
“microbial loop”
0.06
0.6
6
60
100
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
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 < Te
Tc > Te
Tc ~ Te
Are the Oceans
Homogeneous?
Small-scale patchiness
– Marine snow
– Microturbulence
– Vertical differences in light, other factors
Moderate-scale patchiness
– Coastal fronts
– Langmuir circulation
– Ocean eddies or rings
Large-scale patchiness
– Major continental upwelling zones
– Equatorial upwelling zones
– Current convergence zone
– Major ocean gyre systems
Biological Interactions (top down)
– Grazing
– Variations in reproductive rate
– Social behavior
– Interspecific interactions that attract or
repulse