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. Critical depth concept is critical!
Respiration Photosynthesis
Understand why R is a straight line
Understand why P is an exponential curve
Know the difference between:
critical depth
and
compensation depth
Depth

3. Compensation & Critical Depth

4. Annual cycle in N. Atlantic
Nutrients
Light Temperature
Mixing
Mixing
Stratified
Relative increase
Spring
bloom
Fall mini-
Phytoplankton biomass
Zooplankton biomass

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

6. 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

7. 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.

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

9. Biological Pump Photosynthesis Respiration Sinking Remineralization
Chisholm, 2000

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

11. 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

12. Assume a trophic transfer efficiency of 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

13. Traditional view of simple food web: Small things are eaten by (~10x) bigger things
Heterotrophs Autotrophs
20,000
2,000
200 20 2
0.2
Size (μm)

14. Have to add heterotrophic bacteria, heterotrophic protists, and autotrophic bacteria
Heterotrophs Autotrophs
20,000
2,000
200 20 2
0.2
Size (μm)

15. 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
Microbial Loop
Size (μm)
Dissolved organic matter

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

17. Phytoplankton are eaten by zooplankton

18. Plankton size structure is important
Diatoms, dinoflagellates
Coccolithophores, cyanobacteria

19. Importance of microbial loop depends on environmental conditions.

20. 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.

21. 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

22. 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

23. 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

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

25. Draw biomass spectrum here

26. 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

27. =106 metric tons fish per year
=109 metric tons C
per year
=106 metric tons fish per year
Open ocean (90%)
Coastal ocean (9.9%)
Upwelling zones (0.1%)
5 Trophic levels
10% Efficiency
4 Trophic levels
15% Efficiency
2 Trophic levels
20% Efficiency

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

29. 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.

30. 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

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

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

33. Eutrophic vs. Oligotrophic summary
Mixed layer
More mixing Cooler
More stratified Warmer
Nutrients
High concentration
Newer
Low concentration
More recycled
Plankton
Larger
Smaller
Particles
Faster-sinking
Slower-sinking
Carbon Export
More
Less