1. 1 Plankton Ecology and Productivity Productivity and Plankton Abundance Limiting Factors Spatial and Temporal Distribution

2. 2 Primary Production Primary Production: The rate of formation of energy-rich organic products from inorganic material Usually refers only to photosynthesis, although it also includes chemosynthesis Gross Primary Production: The total amount of primary production Net Primary Production: The total amount of primary production after the algae respires (available for higher trophic levels)

3. 3 Measuring Primary Production Usually expressed as g C/m 2 /yr or something similar (C/unit area/unit time) integrated over the entire water column to the bottom of the euphotic zone Euphotic zone: the depth to which light will penetrate (photosynthesis will occur)

4. 4 Measuring Primary Production Oxygen Technique Oxygen released during photosynthesis is used to estimate productivity Includes the addition from photosynthesis and the subtraction from respiration But how do we separate photosynthesis from respiration

5. 5 Light/Dark Bottle Technique

6. 6 Measuring Primary Productivity Oxygen Technique Radiocarbon Radioactive 14 C is used as a tracer in the uptake of bicarbonate during photosynthesis Preferable technique in areas of low productivity Bottles containing phytoplankton and 14 C are placed under optimal light conditions (not in situ)

7. 7 Measuring Primary Productivity Oxygen Technique Radiocarbon Satellite Color Scanning Satellite scanners estimate the relative standing stocks which are then used to estimate changes in production Chlorophyll density is calculated from the ratio of the reflectance of blue to green light Relationship between pigment concentration and primary production varies geographically

8. 8 Satellite Scanning

9. 9 Measuring Primary Productivity Oxygen Technique Radiocarbon Satellite Color Scanning Probe Fluorometer Productivity is estimated by measuring the fluorescence obtained from phytoplankton Photosynthetic pigments fluoresce when exposed to UV light Deployed in the water column and measures photosynthesis directly

10. 10 Factors Affecting Primary Production Limiting Factors: Terrestrial Systems Light Temperature Nutrient Concentration Soil Water

11. 11 Factors Affecting Primary Production Light (Quality and Quantity) Light between 400-720 nm is absorbed by various photosynthetic pigments Chlorophyll a Accessory pigments absorb at a wide range of wavelengths

12. 12 Light Quality and Quantity Light penetrates to different depths based on the angle of incidence (and seasonality) Light of different colors penetrates differently Depth to which light penetrates is a function of the depth of water, amount of phytoplankton, transparency of the water and the differential absorption by other things (e.g., sediments, organic matter)

13. 13 Light Quantity and Quality

14. 14 Photosynthesis vs. Light Intensity

15. 15 Differences Among Species

16. 16 General Trends Light inhibition (photoinhibition) is caused by too much light saturating the photosynthetic centers (generating too much energy which then has to be disposed of) -- this can damage the cell. Also ultraviolet radiation at surface is damaging.

17. 17 Depth vs. Production

18. 18 Compensation Depth Depth where for a given algal cell, photosynthesis = respiration Individual – not population level property Net Production = 0 Usually where light is 1% of the surface intensity, maybe 150 m Varies spatially with water clarity

19. 19 Compensation Point/Depth

20. 20 Photosynthesis and light Commonly, when faced with too much mixing below the compensation depth, cells will lower their metabolic rate or form cysts (resting stages) which can last through the poor conditions.

21. 21 Factors Limiting Primary Production Light Nutrients Needed for enzymes, energy stores, energy carriers and structure Nitrogen and phosphorus are often limiting; Diatoms also need SiO 2 Uptake of nutrients is an active process – often works against a concentration gradient Yet, it is concentration dependent

22. 22

23. 23 Needs for Nitrogen Necessary for the production of proteins, nucleic acids, and ATP In most habitats, N is the limiting nutrient Supply Runoff or Atmospheric Deposition Recycled Ammonium Phytoplankton Zooplankton (Excretion)

24. 24 Phosphorous Critical to energy cycling – i.e., ATP Usually less limiting than N, but there are exceptions Coral reefs: carbonate sediments adsorb P from the water column

25. 25 How do we determine if a nutrient is limiting?

26. 26 Uptake Rate vs. Concentration At low external concentration – uptake depends on concentration At high external concentrations – uptake is saturated

27. 27 Seasonal Succession of Algae

28. 28 Restoring Nutrients Problem: Light – available near the surface Nutrients– down deep where there is no light How do we get the nutrients to the Euphotic Zone? Thermocline/Pycnocline: influences the degree of mixing between surface waters and high nutrient bottom water

29. 29 Thermocline Effects

30. 30 Tropical Polar Temperate

31. 31 High Nutrient (Nitrate) – Low Chlorophyll (HNLC ) Eastern Tropical Pacific Sub-Polar North Pacific Southern Ocean

32. 32 Evidence for Iron Limitation in ETP Macro-nutrients at non-limiting concentrations Small-scale bottle and microcosm experiments Natural additions of iron from land nearby Galapagos Islands

33. 33 IronEx I IronEx II Southern Ocean

34. 34 Factors Limiting Primary Production Light (Quality and Quantity) Nutrients Turbulence As water is mixed, not only will nutrients be carried up, but also algal cells will be carried downward Wind induced turbulence often extends down to 200 m – yet, photic zone is shallower If mixing extends below the critical depth, net production will be negative Especially prevalent at high latitudes

35. 35 Depth of Vertical Mixing

36. 36 Compensation vs. Critical Depth Critical Depth Depth where Gross Photosynthesis = Total Plant Respiration It is a characteristic of the population Compensation Depth Characteristic of individual cells As long as the population (on average) is mixed above the level of the critical depth, the population will have a + net production

37. 37 Spatial Distribution of Phytoplankton Geographical Variation Latitudinal variation

38. 38 Spatial Distribution of Phytoplankton Geographical Variation Latitudinal Differences Regional Differences Continental shelf and open ocean upwelling areas are most productive Shallowness of coastal areas enables the regeneration of nutrients Estuaries: High in nuts, but usually turbid which reduces the depth of photosynthesis Central oceans and gyre centers are nutrient poor

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40. 40 Relative Contribution

41. 41 Geographic Variation in Types Oceanic environments are dominated by small species Large Diatoms and Dinos are common near shores, but rare in the open sea

42. 42 Temporal/Spatial Distribution of Phytoplankton Geographic Variation Seasonal x Geographic Variation

43. 43 Winter Spring SummerFall

44. 44 Factors Limiting Primary Production Light Nutrients Turbulence Zooplankton Grazing What is the relationship between production and consumption? Do herbivores remove microphytoplankton production as fast as it is formed? What percentage of production is taken up by consumers?

45. 45 Production-Consumption Lag

46. 46 Nutrient Recycling How does zooplankton grazing stimulate production? Metabolized algal cells – releases nutrients Bacterial consumption releases “nutrient stocks” Does herbivore pressure limit plankton productivity – i.e., is there top-down control?

47. 47 Temperate Seas North Atlantic Light varies seasonally Thermal structure of the water column changes seasonally Mixing produces two blooms each year Phyto Zoops

48. 48 Tropical Seas Light is available year round Thermal stratification last year round Productivity is low, yet constant Deepest compensation depths What causes the brief peaks and lags? Phyto Zoopl

49. 49 Polar Seas Productivity is restricted to a short period in the polar summer Snow cover disappears long enough to allow light to enter the water When light is available for long periods-bloom occurs Nutrients are not limiting and strong stratification never occur Phyto Zoops

50. 50 Phytoplankton Seasonal Succession Patterns  Temperate waters: small, rapidly growing diatoms in spring give way to larger diatoms in summer. Dinoflagellates dominate in late summer and fall, and small diatoms become dominant again in winter.  Tropical waters: dinoflagellates dominate year around  Polar waters: only summer diatom production

51. 51 Geographical Comparisons of Primary Productivity Tropical Seas 1 ) Well lit all year 2) Thermal stratification all year 3) Low nutrients in surface waters 4) Productivity low but constant year round Temperate Seas 1) Light varies seasonally 2) Seasonal stratification 3) Mixing in winter replenishes nutrients 4) Major PP spring peak, with minor peak in fall Polar Seas 1) Well lit in summer 2) No stratification 3) Nutrients unlimited 4) PP only in ice free summer

52. 52 Temporal/Spatial Distribution of Phytoplankton Geographic Variation Seasonal x Geographic Variation Small Scale Patches Plankton tend to occur in patches Few meters to hundreds of km Samples are often highly variable – “True Replicates?” What causes a patch????

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