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Lecture 6: Plankton

Lecture 6: Plankton. Plankton: Definitions. Plankton : organisms living in the water column, too small to be able to swim counter to typical ocean currents Holoplankton – spend entire life in water column Meroplankton – spend part of life in water column, are benthic for remainder of life.

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Lecture 6: Plankton

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  1. Lecture 6: Plankton

  2. Plankton: Definitions • Plankton: organisms living in the water column, too small to be able to swim counter to typical ocean currents • Holoplankton– spend entire life in water column • Meroplankton – spend part of life in water column, are benthic for remainder of life

  3. Plankton: Definitions • Phytoplankton – photosynthetic protists and bacteria. Single celled or chains of cells. • Zooplankton – nonphotosyntheticprotists and animals. Range from single celled to small vertebrates. • Mixoplankton(or mixotrophic) - can be classified at several different trophic levels

  4. Plankton Size Classes

  5. Position in Water Column • Phytoplankton must be near a source of sunlight • 50-100 m in open ocean • Shallower depths in inshore waters and estuaries • Zooplankton usually feed on phytoplankton, or organisms that feed on phytoplankton

  6. Vertical Position in Water Column • Ways to avoid sinking (neutral buoyancy): • Regulate bulk density (the mass of an organism divided by its total volume) by varying chemical composition • Gas secretion • Body shape • Swim

  7. Vertical Position of Plankton • Smaller organisms denser than seawater sink with a constant velocity, proportional to organismal mass(Stokes’s Law) • Heavier organisms will sink faster than lighter organisms • Irregularly shaped plankton sink slower than predicted by Stokes’s Law

  8. Phytoplankton • Numerous groups, including many flagellated types • High diversity • Different groups have different nutrient needs (e.g., Fe, Si, Ca, P, N) • Different groups have different properties such as bulk density, ability to swim

  9. Phytoplankton • Plantlike Single-celled Protists • Diatoms • Dinoflagellates • Coccolithophores • Silicoflagellates • Green algae • Cryptomonad flagellates • Cyanobacteria

  10. Zooplankton • Crustacean Zooplankton • Copepods • Krill • Cladocera • Others • Gelatinous Zooplankton • Cnidarians • Ctenophores • Salps • Larvacea • Other • Arrow Worms • Pteropods • Planktonic polychaetes • Animal-like Protists • Ciliates • Foraminifera • Radiolaria

  11. Zooplankton

  12. Critical Factors in Plankton Abundance

  13. Major Physical Factors Affecting Primary Production • Temperature • Light • Hydrodynamics • Nutrients

  14. Patchiness of the Plankton & Its Causes • Spatial changes in physical conditions - behavioral responses and population growth/mortality responses • Water turbulence and current transport • Spatially discontinuous levels of grazing • Localized reproduction • Social behavior

  15. Wind and Turbulence • Wind can affect patchiness at a wide range of spatial scales • Langmuir circulation – wind driven water movement creates small vortices which result in small divergences and convergences of water • Result in linear convergences at surface

  16. Directional Flow and Obstructions • Directional water flow can cause persistent spatial patterns in circulation • Flow patterns can be altered at obstructions (islands, mouths of estuaries, passes, etc. )

  17. Depth and Plankton Layers • Phytoplankton and small zooplankton can be concentrated in layers at different water depths

  18. Patchiness of the Plankton • Concentrated patch of phytoplankton must eventually disperse due to the transfer of wind and current energy into kinetic energy

  19. Phytoplankton Patchiness • Population density determined by interaction between turbulence and population growth • Blooms probably caused when you have a rapid increase in phytoplankton growth in an area with restricted circulation

  20. Spring Phytoplankton Bloom • Predictable seasonal pattern of phytoplankton abundance in the temperate and boreal waters of depths of ~10-100m • Spring diatom increase = phytoplankton increase dramatically and are dominated by a few diatom species

  21. Phytoplankton, Zooplankton, Nutrients, and Light Throughout the Year in Temperate-Boreal Inshore Waters

  22. Latitudinal Variation in Cycle

  23. Geographical Comparisons of Primary Production

  24. Light and Phytoplankton • Light irradiance decreases exponentially with increasing depth • Light becomes limiting factor to photosynthesis

  25. Compensation Depth • Compensation depth – the depth at which the amount of oxygen produced in photosynthesis equals the oxygen consumed in respiration Net increase of oxygen over time DEPTH COMPENSATION DEPTH Net decrease of oxygen over time

  26. Compensation Depth • Is controlled by season, latitude, and transparency of water column • Longer photoperiod in temperate-boreal waters • Arctic winter has a zero photoperiod • Suspended matter in coastal waters intercepts light

  27. Photosynthesis and Light Intensity

  28. Before the Spring Phytoplankton Increase • In winter: • Water density is similar at all depths • Wind mixing homogenizes water column • No bloom because any potential profit in photosynthesis would be lost to mixing

  29. Seasonal Changes in Mixing and Light Water column stability is essential to the development of the spring bloom

  30. Key Processes Leading to Spring Phytoplankton Increase Key processes: • Development of thermocline • Trapping of nutrients • Retaining of phytoplankton

  31. Spring Bloom in the Gulf of Maine

  32. Decline of the Spring Phytoplankton Bloom • Nutrients are being removed from stable water column • No replenishment of nutrients from deeper water • Zooplankton grazing has some effect but is often secondary to sinking

  33. Rejuvenation of Conditions for the Spring Phytoplankton Increase • In fall and winter: water cools, water column becomes isothermal with depth, wind mixing restores nutrients to surface waters until conditions are right next spring

  34. Water Column Exchange in Shallow Waters and Estuaries • Importance of water column stability varies with basin depth and season • Benthic-pelagic coupling – nutrient exchange between the bottom and the water column • Fuels more phytoplankton growth

  35. Water Column Exchange in Shallow Waters and Estuaries Benthic-Pelagic Coupling and a Beach Bloom

  36. Water Column Exchange in Shallow Waters and Estuaries • High primary production in estuaries • Nutrient regime is determined by the combination of the spring freshet with mixing and net water flow to the sea

  37. Important Factors in Water Column Exchange in Shallow Waters and Estuaries • Residence time - time water remains in estuary before entering ocean • Rate of nutrient input from watershed • Nutrients may be released to coastal zone

  38. Nutrients • Nutrients are dissolved or particulate substances required by plants and photosynthetic protists; • Can be limiting resources

  39. Nutrients in Marine vs. Terrestrial Environments Terrestrial Marine Ocean waters = 0.00005%N Allows for much less primary production per m3 Short-lived plants Nutrients are often limiting • Agricultural soil = 0.5%N • Allows for greater primary production per m3 • Long-lived plants

  40. Nitrogen– New vs. Regenerated Production • New production: • Nutrients for primary production may derive from input of nutrients from outside the photic zone • Regenerated production: • Nutrients derive from recycling in surface waters from excretion

  41. Phosphorous (P) • P is rapidly recycled between water and phytoplankton • Sediments accumulate P from phytoplankton detritus • Diffusion of P from bottom due to benthic decomposition • Winter mixing returns P to surface waters

  42. N and P as Limiting Nutrients • N and P are depleted by phytoplankton growth • Phytoplankton more enriched in N than P, suggesting that N is limiting to primary production on the scale of the entire ocean • P ultimately comes from weathering of minerals

  43. Silicon • Important limiting element for diatoms • Sinking of diatoms from surface waters removes silicon • Silica (Silicon dioxide) delivered to ocean by wind and river transport

  44. Fe, Si often enter the ocean by wind-borne particles

  45. Iron as a Limiting Nutrient and in Climate Change • Is commonly in short supply and is thus limiting to phytoplankton • May be crucial in parts of the ocean where nitrogen appears not to be limiting factor (HNLP zones) • Phytoplankton sequester large amounts of CO2 during photosynthesis • Dr. John Martin – Idea was that if you increase phytoplankton production, you could slow global warming • Evidence – Eruption of Mount Pinatubo in 1991

  46. IronEx Studies • IronEx I (1993) – First open ocean iron fertilization experiment • Single iron addition to a 100 km2patch of water near Galapagos Islands • Results not very dramatic • Proved that iron can limit primary production in some of the world’s oceans • IronEx II (1995) - Sequential additions of solubilized iron to water patch in Equatorial Pacific • Produced enormous phytoplankton bloom • Have been 13 iron fertilization experiments since 1993

  47. Intense and Harmful Algal Blooms • Conditions: 1. A stable water column 2. Input of nutrients 3. Sometimes an initial input of resting stages • Principally some dinoflagellates and cyanobacteria • Population crashes may reduce oxygen in water

  48. Red Tide off Florida Coast

  49. Phytoplankton Succession • Seasonal change in dominance by different phytoplankton species • General properties correspond to the seasonal trend in nutrient availability

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