Zooplankton

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Zooplankton
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Chaoborus, Chironomidae

• Complex life history (benthic, aquatic juvenile,
  emergent adult)
• Major predators on macrozooplankton but sporadic
  abundance

Lake Victoria
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Rotifera

• 100 planktonic taxa, most abundant zoop
• Name from rotating corona
• Rapid development bloom
• Parthenogenetic (faculative)
• Female Egg Female
• Egg fertilized by male

Male and Female
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Rotifers

• Up to 200 µm in size
• Omnivorous, eat picoplankton and nanoplankton,
  flagellates, ciliates to up 40 µm

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Crustaceans
Cladocerans
Copepods

• Chitin carapace, 0.2- 3 mm
• Tactile antennae
• Bisexual, 11-molt development, diapause
• Adjustable pigments

• Chitin carapace
• Antennae for movement, eyes
• Parthenogenetic, slower development than Rotifers
• Transparent
• Resting stage, ephippia

1 mm
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Crustaceans
Copepods
Cladocerans

• Hop/sink swimmers
• Selective filter feeders (size, taste)
• Hungry
• Linked to clear-water phase

• Efficient swimmers
• Predators and detritovores
• Abundant in oligotrophic, dystrophic lakes

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Seasonal Abundance
Algae
Zooplankton

• Grazing dynamics,
• efficiency
• Temperature
• Reproduction cycles
• Predation

Fish
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Brooks and Dodson, 1965
Crystal Lake, CT 1942 average zoop size 0.8
mm Daphnia, Copepods No Alewife 1964 Average
zoop size 0.3 mm Huge rotifer bloom, small
Daphnia, copepods Zooplanktivorous Alewife
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Experiment Manipulations

• Hrbacek, 1961

• 1957 Poltruba fish poisoned by toxic bloom,
  restocked with
• largemouth bass

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• Piscivores vs. Zooplanktivorous fish

Zooplanktivores Zooplankton
Hrbacek, 1957 Trophic Cascade
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Zooplankton and Nutrients
Algae

• Top-down phytoplankton control, bottom-up
  stimulation
• Stabilizing feedback

Zooplankton
Bacteria
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Zooplankton and Nutrient Cycling
Elser et al., 2000 Grazer Stoichiometry

• Herbivores lower C (N,P) than food
• Lower NP than food
• Herbivores release N
• N supplement affects algae
• Decrease CP of food (negative feedback)

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Conclusions

• Rotifers, Cladocerans, and Copepods are the most
  common zooplankton in lakes
• Zooplankton abundance is controlled by
  interactions between food abundance, fish
  predation, and zoop reproductive cycle
• Changes in fish abundance and predation can have
  major effect on zoop populations, and thereby
  phytoplankton populations
• Zooplankton grazing exerts major control on lake
  metabolism, nutrient cycling