1. Food web and microbial loop Eutrophic vs. Oligotrophic food webs
Review
Seasonal cycle
spatial variation
Food web and microbial loop
Eutrophic vs. Oligotrophic food webs
Biological pump

2. Compensation & Critical Depth

3. Latitudinal variation in seasonal cycles driven by variation in irradiance
[Also Irradiance]
90oN = N. Pole
60oN ~Anchorage,AK
30oN ~N. Florida
0oN = Equator

4. Mixed layer is deeper in Atlantic than in Pacific
Atlantic Ocean
Depth (m)
South pole Equator North Pole
Pacific Ocean
Depth (m)
South pole Equator North Pole
Temperature

5. Annual cycles in other regions
Phytoplankton biomass
Zooplankton biomass
Try this on your own: Draw the vertical profiles of temperature and light and the critical depth for each region as we did in class for the North Atlantic.

6. Phytoplankton Irradiance
Physical mixing
processes
Nutrients
Irradiance
Zooplankton
Higher Trophic Levels
Sinking & Senescence
Particle Dynamics
Particle Flux (Carbon flux)

7. Biological Pump Photosynthesis Respiration Sinking Remineralization
Chisholm, 2000

8. On average, predators are ~10x bigger than prey
ESD = Equivalent Spherical Diameter
Hansen et al. 1994

9. What’s in a liter of seawater?
1 Liter of seawater contains:
1-10 trillion viruses
1-10 billion bacteria
~0.5-1 million phytoplankton
~1,000 zooplankton
~1-10 small fish or jellyfish
Maybe some shark, sea lion, otter, or whale poop
This basking shark can filter
~25,000 L seawater per day!
*The bigger you are,
the fewer you are

10. trophic transfer efficiency is ~10%
Basic assumption:
trophic transfer efficiency is ~10%
Biomass 10
100
1000
Efficiency
0.1
fish
zooplankton
phytoplankton
Trophic transfer efficiency = fraction of biomass consumed that is converted into new biomass of the consumer

11. Small things are eaten by (~10x) bigger things.
Heterotrophs Autotrophs
20,000
2,000
200 20 2
0.2
Fish
Zoo- and
Phyto-
Plankton
Protists
Bacteria
Size (μm)

12. Dissolved organic matter
Bacteria absorb organic molecules leaked by microbes and phytoplankton. This creates a microbial “loop.”
Heterotrophs Autotrophs
20,000
2,000
200 20 2
0.2
Fish
Zoo- and
Phyto-
Plankton
Protists
Bacteria
Microbial Loop
Size (μm)
Dissolved organic matter

13. Zoom in on food web
Photosynthesis respiration
Chisholm, 2000

14. Plankton size structure is important indicator of nutrient conditions
Diatoms, dinoflagellates
Copepods, Krill
Coccolithophores, cyanobacteria
Protists

15. Importance of microbial loop depends on environmental conditions.

16. Definitions
Eutrophic environments have high nutrient concentrations and high productivity. Coastal upwelling regions and estuaries are Eutrophic.
Oligotrophic environments have low nutrients and low productivity. Subtropical gyres (open ocean) are Oligotrophic.
It takes a lot of mixing or a big nutrient influx to make an environment eutrophic. Stratified systems eventually must become oligotrophic.

17. Diatom bloom in Barents Sea
Eutrophic
-coastal
-estuaries
-upwelling
-high latitudes
Oligotrophic
-open ocean
-central gyres
Clear water over Great Barrier Reef
Diatom bloom in Barents Sea

18. In oligotrophic systems, small phytoplankton (e. g
In oligotrophic systems, small phytoplankton (e.g. cyanobacteria) dominate and biomass goes through more levels of plankton to get to fish.
Temp.
Depth
Dcr
Microbial loop is key

19. Microbial loop is less important
In eutrophic systems, large phytoplankton (diatoms) dominate and more biomass goes directly to large plankton and fish.
Temp.
Depth
Dcr
Microbial loop is less important

20. Oligotrophic Eutrophic
Open Ocean
Tuna
Carniv. Fish
Carniv. Plankton
Herbiv. Plankton
Phytoplankton
5 Levels
10% Efficiency
(between levels)
Coastal Ocean
Carniv. Fish
Carniv. Plankton
Herbiv. Plankton
Phytoplankton
4 Levels
15% Efficiency
(between levels)
Upwelling Zone
Anchovies
Phytoplankton
2 Levels
20% Efficiency
(between levels)

21. Draw biomass spectrum here

22. Area
% of ocean area
Total Plant
Production
Transfer
Efficiency
Trophic
Levels
Estimated
Fish Production
(x109 metric tons carbon
per year)
(x106 metric tons
Open
Ocean
90.0 39
10% 5 4
Coastal
9.9
8.6
15% 29
Upwelling
Zones
0.1
0.23
20% 2 46

23. =106 metric tons fish per year
=109 metric tons C
per year
=106 metric tons fish per year
Open ocean (90% of area)
Coastal ocean (9.9% of area)
Upwelling zones (0.1% of area)
5 Trophic levels
10% Efficiency
4 Trophic levels
15% Efficiency
2 Trophic levels
20% Efficiency

24. Food-web structure affects the export of carbon to deep ocean
Photosynthesis respiration
Chisholm, 2000

25. How does organic matter get to the bottom of the ocean?
Dead cells and fecal pellets (plankton poop) sink. Big ones sink faster.
Dissolved organic matter, pieces of gelatinous animals etc. stick together and form bigger “marine snow” that sinks.
Organic debris is collectively known as Detritus.

26. Bigger plankton sink faster
Bigger plankton sink faster. They also have bigger, faster-sinking fecal pellets.
Marine
snow
Large plankton
and their
fecal pellets
Small plankton

27. In oligotrophic conditions, there are fewer, smaller particles that sink more slowly into deep ocean.
Temp.
Depth
Dcr
small
fecal
pellets

28. In eutrophic conditions, there are more, larger particles that sink into deep ocean.
Temp.
Depth
Dcr
Large
fecal
pellets
Large
Marine snow

29. Eutrophic vs. Oligotrophic worksheet
system
Oligotrophic system
Mixed layer:
mixing intensity
temperature
Nutrients:
concentration
amount of recycling
Plankton:
size range
sinking speed
Particles:
Carbon Export
(amount)