Review Phytoplankton competition Critical and Compensation Depth Spring bloom Spatial variation in seasonal cycle Biolo

1. Review • Phytoplankton competition • Critical and Compensation Depth • Spring bloom • Spatial variation in seasonal cycle • Biological pump • Plankton size structure • Classic food web • Microbial loop • Eutrophic vs. Oligotrophic food webs

2. Irradiance = power of electromagnetic radiation per unit area of ocean’s surface (e.g. Watts/m2). • Only a small fraction (the PAR) is used for photosynthesis.

3. Competition for nutrients Equal max Ks1<Ks2 At low N, Sp. 1 wins max2 > max1 Equal Ks 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

4. Compensation & Critical Depth

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

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

8. 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!

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

10. 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

11. Annual cycles in other regions Lalli & Parsons

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

13. 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.

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

15. Grazers in the ocean (Zooplankton) • Protists - single cells • Engulf food • Narrow size range of food • Gelatinous animals - • -“Hoover” or stick to prey • -Wide size range of food • Crustaceans - • -“Handle” their food • -Narrow size range of food ciliates jellyfish salps krill copepods

16. Biological Pump Chisholm, 2000

17. Phytoplankton are eaten by zooplankton

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

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

20. 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

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

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

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

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

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

26. Productivity sets the potential fisheries yield Eutrophic systems Oligotrophic systems

27. Make-up of the food web varies with environmental conditions. Microbial loop

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

31. Oligotrophic Ecosystems differ in coastal and open ocean Eutrophic

32. 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

34. What does structure of the food web have to do with the biological pump?

35. Organic matter has to get to the dump truck at 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.

36. Marine snow particles from Offshore of New Jersey Dust bunnies of the sea!

37. 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

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

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

40. Eutrophic vs. Oligotrophic summary