Temporal and Spatial Distribution of Phytoplankton

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Temporal and Spatial Distribution of Phytoplankton

• Introduction
• Vertical distribution
• Horizontal distribution
• Seasonal changes
• Factors affecting phytoplankton succession

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Introduction

• Aquatic vs. terrestrial plant distribution
• Review of terminology
• seston
• plankton
• nekton
• plant communities

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Size classes of plankton

• ultraplankton lt 10 µm
• nanoplankton lt 67 µm
• net plankton gt 67 µm

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Spatial Distribution of Plankton

• Vertical distribution
• Passive Movement Sinking!
• Archimedes Principle
• F gkd3 (p'-p)
• where p density of body
• p density of liquid
• g gravitational acceleration
• kd3 volume of the body, where
• d is a linear measurement

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• Stokes Law
• the drag force on a sphere
• F 3 pµV0d
• where V0 velocity
• µ dynamic viscosity
• d diameter of sphere

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• Therefore,
• sinking velocity slows viscosity ?
• sinking velocity slows excess density of the
• object over the medium ?
• sinking velocity slows radius2 ?

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• Vertical distribution affected by
• specific gravity adjustments
• - oil and gas vacuoles
• - ex blue-green algae
• - selective accumulation of ions
• - ex green algae

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• 2. Form resistance e.g. orthogonal projections
• - ex centric diatoms
• 3. Size
• - microplankton settle slowly!

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• 4. Water movement, calm vs. wind-mixed
  distribution

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• Active movement
• Vertical migration
• Ex flagellates
• Phototaxis
• Positive- movement towards the light
• Negative- movement away from the light
• Geotaxis
• Resistance to sinking, ex zooplankton

Horizontal Concentrations
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Seasonal Changes in Phytoplankton Populations

• Factors increasing phytoplankton numbers
• Favorable changes in temperature
• " " light
• " " nutrients
• Each species of algae has a range of tolerance to
  environmental extremes growth and reproduction
  is enhanced by optimal combinations of these
  factors

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• Factors decreasing phytoplankton numbers
• Grazing by zooplankton (and some fish)
• Depletion of nutrients
• Parasitism, e.g. fungi, competition for resources

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• Sedimentation
• Unfavorable light, temperature, etc.
• Toxins produced by other phytoplankton

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Factors affecting phytoplankton succession or the
relative abundance of species include

• Light and Temperature

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Temperature Requirements of Phytoplankton

• Oligothermal cold requiring
• Ex trout
• Polythermal warm requiring
• Ex tilapia
• Eurythermal tolerant of wide temperature ranges
• Ex carp, catfish

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• Turbulence
• Ex streams or waves over periphyton
• Concentration of nutrients
• Ex end of diatom maximum due to silica depletion
• Ex succession of phytoplankton species

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• Growth promoting and growth inhibiting substances
  and nutrient competition
• Blue-greens can produce a factor which inhibits
  growth of other algae
• Aquatic macrophytes may also inhibit algal growth
  by shading out phytoplankton and competing for
  available nutrients
• Metabolites and anti-metabolites

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Polar vs. Temperate vs. Tropical
Little winter growth, large seasonal amplitude
Small seasonal variation
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• Polar Lakes
• A single peak usually occurs in mid-summer
• Temperate Lakes
• Increase in total biomass in early spring due to
  increased light, max in April, then decline
• Second max (usually smaller), maybe in autumn due
  to increased water circulation (i.e. nutrient
  supply)

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Phytoplankton Community Ecology

• Paradox of the plankton
• Possible explanations
• Niche diversification due to
• Physical niche diversification
• Predation
• Commensalisms and symbiosis
• Differences in resource utilization efficiencies

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• Theory of the temporal niche
• Phytoplankton have relatively low competition
  coefficients
• Phytoplankton reproduce rapidly
• Physical factors change through time
• Time scale in plankton populations relative to
  their reproductive period
• Non-equilibrium community
• Theory of recruitment from littoral flora

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