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Phytoplankton Dynamics

Phytoplankton Dynamics. Primary Productivity (g C/m 2 /yr) Gross (total) production = total C fixed Net production = C remaining after respiration Standing crop = biomass present at a point in time. Factors Affecting Primary Production. Light Nutrients

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Phytoplankton Dynamics

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  1. Phytoplankton Dynamics Primary Productivity (g C/m2/yr) Gross (total) production = total C fixed Net production = C remaining after respiration Standing crop = biomass present at a point in time

  2. Factors Affecting Primary Production • Light • Nutrients • Loss out of the photic zone due to sinking or mixing • Grazing

  3. 1. Light Light penetration – affected by • Angle of incidence • Surface reflection • Suspended particles • Adsorption by the water itself

  4. Water absorption of light

  5. DC = Compensation depth At DC ---- primary production (P) = respiration (R) in each algal cell IC = Compensation light intensity

  6. 2. Nutrients • Nutrients = essential elements needed for cell maintenance and growth N, P, Si, Ca, K, etc. • N and P in ocean water about 10,000 x less than on land (“ocean desert”) • Redfield ratio C:N:P 105:16:1 same in seawater and pp cell

  7. Body form of pp adapted for nutrient uptake • Rate of uptake is concentration dependent low nutrient species – very efficient at nutrient uptake in low concentrations, but rate saturates out at high concentrations high nutrient species – less efficient uptake at low concentrations, but can exploit high concentrations

  8. 3. Loss out of the photic zone • Sinking • Water turbulence mixes plankton deeper into the water column DM = mixing depth Vertical mixing can take plankton below the compensation depth

  9. DC = compensation depth, (P = R in each pp cell) DCR = critical depth, (P = R in whole pp population) DM < DCR PW > RW DM > DCR PW < RW

  10. 4. Grazing • Copepods can have extremely high grazing rates GR < PW GR = PW GR > PW

  11. Winter Spring Summer Fall

  12. DCR moves up in the water column – photic zone smaller

  13. What happens in late spring/early summer?

  14. Zooplankton – grow and reproduce in spring, GR??

  15. Spring  Summer Fall Magnitude of fall bloom -- timing, when DM falls below DCR

  16. Idealized Chart

  17. Why are the polar oceans different? Light in spring No thermocline Grazing?

  18. Why are the tropical oceans different? Permanent thermocline Nutrients always low Blips?

  19. What’s different between the Atlantic and Pacific? Copepod life history – lag time

  20. Coast vs. Open Ocean • Coast receives nutrients from land • Upwelling • Shallow water depth – bottom shallower than the DCR • Thermocline not as well developed or persistent • Turbidity of water can counteract other factors

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