Toxin production in migrating dinoflagellates: a modelling study of PSP producing Alexandrium

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Toxin production in migrating dinoflagellates a
modelling study of PSP producing Alexandrium

• Kevin J. Flynn

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(No Transcript)
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Introduction

• Nutrient status affects toxin synthesis
• Migration and PSP production not mutually
  exclusive (MacIntyre et al. 1997)
• N-limited batch cultures had lower PSP
• Poorly understood complex interaction between
  light, N and P nutrition

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From http//dinos.anesc.u-tokyo.ac.jp/HP2002/Jpeg/
Alexandrium/aff-tam-cat.-fun.jpg
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Model development
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Model development (Flynn and Fasham, 2002)

• Light attenuation is function of depth, as well
  as the overlaying biomass of other populations
  and its own biomass
• All four populations grown together
• Photo-inhibition overrode any ascent stimulus
  highest position in water column optimized
  photosynthesis

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Model development

• Toxin synthesis promoted in low light, high N,
  and low P
• Three different NP ratios used
• Four populations grown in each of the four NP
  scenarios
• Depth max 10m, migration rate 24m/day
• Normal light/dark cycle for summer at 45ºN

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Results
Best Pop 1 high Nred, recycled toxic-N Worst
Pop 4 low Nred, lost toxic-N
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Migration patterns
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Migration patterns

• Phase 1 migrate down to avoid photo-inhibition,
  ends upon nutrient limitation
• Biomass accumulation leads to shallower depth
• Phase 2 intermediate depths, sufficient light,
  surface migration unnecessary
• Duration depends on biomass accumulation
• Phase 3 extreme migration to surface for light
  due to light attenuation
• Asynchronous populations not subject to
  self-shading

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Toxin content per biomass
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Toxin content per biomass

• Scenario 1 highest in phase 1, N-limitation
  after day 5, remained low throughout
• Scenario 2 recovery in phase 3, light limitation
  lowered relative mineral-nutrient limitation,
  greater migration resulted
• Scenario 3 same P as Scenario 2, but twice N
• Higher Nred higher toxin content
• Scenario 4 lowest P and biomass, highest toxin
  content

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Toxin per liter of water (external of cell?)
Content per biomass
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Discussion

• Subsurface maximum biomass depended on nutrient
  status
• Photo-inhibition prevented migration to surface
  unless accumulation caused light attenuation
• Migration patterns not always rhythmic or truly
  diurnal
• Unclear toxin content graphs (within same graph)
• Difficult to differentiate population lines
• Text did not always coincide with graph

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Discussion

• Highest toxin content in prolonged P-stress
• Lowest in N-starvation (but never starved?)
• Fastest synthesis during N-refeeding(?)
• Toxicity depends not only on NP ratios, but also
  absolute concentrations
• Still to test natural irradiance, temperature

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Alexandrium fundyense
Alexandrium fundyense
Alexandrium tamarense
Alexandrium tamarense cysts