Open Oceans: Pelagic Ecosystems

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Open Oceans Pelagic Ecosystems
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Elements of an Ecosystem Approach

• What are the components?
• What are the special environmental challenges?
• What are the special adaptations?
• How do we understand form function?
• What are the controlling processes?
• What are the important patterns?

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Pelagic System Components

• The area of open water of oceans, including the
  entire water column away from the bottom
  substrates
• Nutrients and salts
• Plankton
• Nekton

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Dimensions of Variation for Plankton

• Size virus (2 x 10-7 m) to jellyfish (0.2 m)
• Energy processing nutritional modes
• photosynthetic (phytoplankton)
• heterotrophic, ingestive (zooplankton)
• heterotrophic, absorptive (mycoplankton)
• infective (viroplankton)
• Life history variation
• permanent residents
• transient members of the plankton community

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Phytoplankton
Dinoflagellates
Foraminifera
Diatoms
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Coccolithophores
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Coccolithophore bloom, English Channel
20 km
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Diversity of form
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Zooplankton protista
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Mixture of groups producing a bloom
Baltic Sea
1 Coccolithophores 2 Diatoms 3 Eukaryotic
picoplankton
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Zooplankton crustacea
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Copepod
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Zooplankton larvae
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Challenges

• Maintaining access to nutrients, light,
  resources
• Avoid being food for larger consumers

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Adaptations for maintaining position

• Use water movements
• Convection cells (from diurnal cycles in heat)
• Langmuir convection cells from wind

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Langmuir patterns in the Galapagos
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Adaptations for maintaining position

• Affect buoyancy
• Use lighter ions for osmotic balance (e.g., use
  chlorides rather than sulphates)
• Develop flotation organs (gas, oils, fats)
• Manipulate resistance (use viscosity)
• parachute morphology
• elaborate appendages

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Global scale patterns of pelagic productivity
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What are controlling processes?

• Primary Productivity
• Different estimates of productivity
• Gross Primary Productivity
• Net Primary Productivity
• Standing crop
• and Grazing Rates

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What is productivity?

• primary productivity is defined as the total
  quantity of carbon fixed by autotrophs
• a rate expressed as grams of carbon fixed per
  square meter of sea-surface per unit of time
• gross primary production is the total amount of
  organic matter produced by autotrophs
• net primary production is the energy remaining
  after respiratory needs have been met
• NPP Gross Primary Production - Respiration

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Questions to consider

• Why should we care about patterns of biological
  productivity in oceans?
• What are the spatial patterns of productivity?
• What mechanisms promote or limit productivity?

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Why should we care about productivity?

• Photosynthetic activity in oceans created current
  O2-rich atmosphere
• Plankton form ocean sediments fossil fuels
• Plankton are a critical part of carbon pump
  that influences atmospheric CO2
• Phytoplankton form the base of food webs and
  associated biological diversity
• Limits to productivity may limit the amount of
  harvestable biomass from ocean ecosystems

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Measuring Primary Productivity Data

• Standing crop methods
• Chlorophyll concentration (water extraction,
  satellite)
• Cell counts (flow cytometers)
• Rate measurements
• Light-dark bottle method
• Carbon-14 uptake
• Advantages disadvantages

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chlorophyll density temperature
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Link between producers grazers
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Measuring Primary Productivity Inferences

• Simple models integrate different parameters to
  estimate rates of productivity
• Model components (Field et al. Science
  281237-240)
• chlorophyll concentration
• water depth in photic zone
• fraction of water column where photosynthesis is
  light-saturated
• surface temperature

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Results of productivity model
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Some patterns

• average primary productivity in the oceans is 50
  g C/m2/yr
• 300 g C/m2/yr considered relatively high rate of
  primary productivity 
• low rates of primary productivity typically 20 to
  30 g C/m2/yr