Plankton Ecology and Productivity

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Plankton Ecology and Productivity

• Productivity and Plankton Abundance
• Limiting Factors
• Spatial and Temporal Distribution

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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
  plant respires (available for higher trophic
  levels)

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Measuring Primary Production

• Usually expressed as g C/m2/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)

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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

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Light/Dark Bottle Technique
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Measuring Primary Productivity

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

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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

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Satellite Scanning
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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

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Factors Affecting Primary Production

• Limiting Factors Terrestrial Systems
• Light
• Temperature
• Nutrient Concentration
• Soil
• Water

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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

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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)

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Light Quantity and Quality
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Photosynthesis vs. Light Intensity
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Differences Among Species
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Depth vs. Production
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Compensation Depth

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

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Compensation Point/Depth
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Factors Limiting Primary Production

• Light
• Nutrients
• Needed for enzymes, energy stores, energy
  carriers and structure
• Nitrogen and phosphorus are often limiting
• Diatoms also need SiO2
• Uptake of nutrients is an active process often
  works against a concentration gradient
• Yet, it is concentration dependent

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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

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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

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How do we determine if a nutrient is limiting?
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Uptake Rate vs. Concentration
At low external concentration uptake depends on
concentration At high external concentrations
uptake is saturated
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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

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Thermocline Effects
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High Nutrient (Nitrate) Low Chlorophyll (HNLC)
Eastern Tropical Pacific Sub-Polar North
Pacific Southern Ocean
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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
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IronEx I IronEx II
Southern Ocean
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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

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Depth of Vertical Mixing
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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

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Spatial Distribution of Phytoplankton

• Geographical Variation
• Latitudinal variation

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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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Relative Contribution
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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

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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?

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Production-Consumption Lag
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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?

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Temperate Seas

• North Atlantic
• Light varies seasonally
• Thermal structure of the water column changes
  seasonally
• Mixing produces two blooms each year

Phyto
Zoops
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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
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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
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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
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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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Seasonal Succession of Algae
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Temporal/Spatial Distribution of Phytoplankton

• Geographic Variation
• Seasonal x Geographic Variation

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Spring
Winter
Summer
Fall