Review Competition for nutrients Light Critical and Compensation Depth

1. Review • Competition for nutrients • Light • Critical and Compensation Depth • Seasonal cycle and spatial variation • Plankton size structure • Food web and microbial loop • Eutrophic vs. Oligotrophic food webs • Biological pump

2. Competition for nutrients Equal max Ks1<Ks2 At low N, Sp. 1 wins max2 > max1 Equal Ks At low N, Sp. 1 wins (but barely) At high N, Sp. 2 wins max2 > max1 Ks1<Ks2 At low N, Sp. 1 wins At high N, Sp. 2 wins Species 1 Species 2 Specific Growth Rate  Max growth rate (a constant) Half-saturation constant (a constant) Nutrient Concentration N

3. Irradiance = power of electromagnetic radiation per unit area of ocean’s surface (e.g. Watts/m2). • Only visible light is used for photosynthesis. • Light attenuates with depth. • Longer wavelengths attenuate faster because of greater absorption by particles. Irradiance depth

4. Compensation & Critical Depth

5. Seasonal evolution of mixed layer

6. Annual cycle in N. Atlantic Phytoplankton biomass Zooplankton biomass Spring bloom Fall mini- bloom Nutrients LightTemperature Mixing Mixing Stratified Relative increase

7. Definitions • Autotrophs get their carbon and energy from inorganic sources. Phytoplankton are autotrophs because they get their carbon from CO2 and energy from light. • Heterotrophs get their carbon and energy from pre-formed organic matter. Zooplankton are heterotrophs because they get carbon and energy by eating phytoplankton. • Eutrophic environments have high nutrient concentrations and high productivity. Coastal upwelling regions are Eutrophic. • Oligotrophic environments have low nutrients and low productivity. Subtropical gyres (open ocean) are Oligotrophic.

8. Primary production and its seasonal cycle vary greatly in space Chl a from SeaWIFS satellite

9. 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

10. Nutrient limitation varies among oceans • Mixed layer is deeper in Atlantic than in Pacific • Silicon is important for the growth of diatoms.

11. Atlantic vs. Pacific spring bloom Phytoplankton biomass Zooplankton biomass Winter: Deep mixed layer, Production shuts down Spring: Phytoplankton bloom Zooplankton - slow to catch up Winter: Shallower mixed layer, Continuous low production Spring: Phytoplankton bloom Zooplankton - right there to eat the bloom!

12. Spring in the Arctic is darker & colder than winter at mid-latitudes [Also Irradiance] 90oN = N. Pole 60oN ~Anchorage,AK 30oN ~N. Florida 0oN = Equator

13. Seasonal cycle varies with latitude Nutrients Light [Nutrient] Latitude Light Winter Spring Summer Autumn Winter Lalli & Parsons

14. Annual cycles in other regions Lalli & Parsons

15. Bacteria are an important part of the biological pump. They turn organic carbon and nutrients back into inorganic carbon and nutrients. (“remineralizing”) Bacteria

16. Some grazers in the ocean (Zooplankton) • Protists - single cells • Gelatinous animals • Crustaceans ciliates jellyfish salps krill copepods

17. Plankton drift with the currents Nekton can swim against currents 1 m 1 mm 1 cm 1 m Sieburth et al. 1978

18. 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 *The bigger you are, the fewer you are

19. Traditional view of simple food web:Small things are eaten by (~10x) bigger things Heterotrophs Autotrophs Size (m)

20. Have to add heterotrophic bacteria, heterotrophic protists, autotrophic microbes Heterotrophs Autotrophs Size (m)

21. Bacteria absorb organic molecules leaked by microbes and phytoplankton. This creates a microbial “loop.” Heterotrophs Autotrophs Size (m) Dissolved organic matter

22. Assume a trophic transfer efficiency of 10% Biomass 10 100 1000 Efficiency 0.1 0.1 fish zooplankton phytoplankton

23. Biological Pump Photosynthesis respiration Chisholm, 2000

24. Phytoplankton are eaten by zooplankton

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

26. Importance of microbial loop depends on environmental conditions. Microbial loop

27. Eutrophic -coastal -estuaries -upwelling Oligotrophic -open ocean -central gyres Transparent L. Tahoe Diatom bloom in Barents Sea

28. 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

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

30. 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

32. How does food-web structure affect the export of carbon to deep ocean?

33. Organic matter has to get to the bottom of the ocean somehow. • 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.

34. Bigger plankton sink faster. They also have bigger fecal pellets that sink faster. Large plankton and their fecal pellets Marine snow Small plankton and their fecal pellets

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

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

37. Eutrophic vs. Oligotrophic summary