1. 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

2. Factors Affecting Primary Production 1. Light 2. Nutrients 3. Loss out of the photic zone due to sinking or mixing 4. 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

6. D C = Compensation depth At D C ---- primary production (P) = respiration (R) in each algal cell I C = Compensation light intensity

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

9. Body form of pp adapted for nutrient uptake Body form of pp adapted for nutrient uptake Rate of uptake is concentration dependent 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

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

11. D C = compensation depth, (P = R in each pp cell) (P = R in each pp cell) D CR = critical depth, (P = R in whole pp population) (P = R in whole pp population) D M R W D M R W D M > D CR P W D CR P W < R W

12. 4. Grazing Copepods can have extremely high grazing rates Copepods can have extremely high grazing rates GR < P W GR = P W GR > P W

14. WinterSpringSummerFall

15. D CR moves up in the water column – photic zone smaller

16. What happens in late spring/early summer?

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

18. Spring  Summer Fall Magnitude of fall bloom -- timing, when D M falls below D CR -- timing, when D M falls below D CR

19. Idealized Chart

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

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

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

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