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Zooplankton - PowerPoint PPT Presentation

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Zooplankton. Zooplankton. Planktonic animals can be found in almost all animal phyla Most zooplankton belong to 3 major groups: rotifers, Cladocera, and Copepoda. Zooplankton. One other group may, at times, be important: Protozoa

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  • Planktonic animals can be found in almost all animal phyla

  • Most zooplankton belong to 3 major groups: rotifers, Cladocera, and Copepoda


  • One other group may, at times, be important: Protozoa

  • Spend only portion of lives in plankton (mostly sediment-dwelling)

  • Feed on bacteria, detritus (little used by other zooplankton)


  • Mostly littoral, sessile, but some are completely planktonic

  • May be dominant zooplankton in some lakes

  • Omnivorous, small (<12 µm)

  • Filter-feeding with corona


  • Some are predatory

  • Asplanchna

  • Feed on protozoa, other rotifers, small crustaceans

Rotifer reproduction
Rotifer Reproduction

  • Reproduction during most of growing season by diploid female parthenogenesis

  • Diploid eggs produced via mitosis

  • Develop into amictic females

  • Continues for generations during good conditions

Rotifer reproduction1
Rotifer Reproduction

  • Environmental stress causes changes

    • Drop in temperature

    • Crowding (food)

    • Accumulation of pheromones from females

    • Reduced availability of food components (e.g., vitamin E)

Rotifer reproduction2
Rotifer Reproduction

  • Mictic females develop, produce haploid eggs via meiosis

  • Unfertilized eggs develop into males

  • Mate with mictic females to produce thick-walled resting eggs

Rotifer reproduction3
Rotifer Reproduction

  • Resting eggs resistant to adverse environmental conditions

  • Eggs remain in diapause until return of favorable conditions

  • Hatch into amictic females

Rotifer population dynamics
Rotifer Population Dynamics

  • Different species exhibit different population peaks

  • Some in early summer, others in winter/early spring, others multiple times in summer

Rotifer cyclomorphosis
Rotifer Cyclomorphosis

  • Seasonal polymorphism

  • Elongation, enlargement or reduction, production of spines

Rotifer cyclomorphosis1
Rotifer Cyclomorphosis

  • Reduce sinking rate in warmer water

  • Cope with larger prey

  • Better resist predation


Rotifer cyclomorphosis2
Rotifer Cyclomorphosis

  • Spines prevent ingestion of Brachionus by Asplanchna

  • Formation of spines induced by organic substance (kairomone) produced by predator

Rotifer use by fish
Rotifer Use by Fish

  • Too small to be important as food for most fish

  • May be important in diets of some larval fish

  • Rotifers are potential prey for predatory copepods

  • Vertical migration upward at midday to avoid copepods


  • Small crustaceans (0.2-3.0 mm) with head, and body covered by bivalve carapace

  • Swim by using large 2nd antennae

  • Filter phytoplankton, detritus for food (some are predators)


  • Size of phytoplankton ingested proportional to body size

  • Rate of filter feeding increases with size and temperature

  • Selective filtering by cladocerans can remove big “chunks” of the phytoplankton, and alter phytoplankton succession

Cladocera reproduction
Cladocera Reproduction

  • Reproduction similar to that of rotifers

  • Parthenogenesis by diploid females throughout most of the growing season

  • Continues until interrupted by unfavorable conditions

Cladocera reproduction1
Cladocera Reproduction

  • Temperature reductions, drying, reduced photoperiod, crowding (competition for food), decrease in food size/quality

Cladocera reproduction2
Cladocera Reproduction

  • Some eggs develop into diploid males

  • Females produce haploid eggs

  • Mate with males

  • Fertilized eggs overwinter in thickened brood pouch - ephippium

Cladocera reproduction3
Cladocera Reproduction

  • Ephippia can withstand severe conditions

  • Can be transported by birds to other waters

  • Hatch under favorable conditions into parthenogenetic females

Population dynamics
Population Dynamics

  • Similar to those of rotifers

  • Some overwinter as adults, others as resting eggs (ephippia)

  • Increased food and temperature enhance production

Diurnal vertical migrations
Diurnal Vertical Migrations

  • Most migrate to surface at dusk, downward at dawn (light intensity the stimulus)

  • Movements may be >50 m and rapid (20 m/hr)

Diurnal vertical migrations1
Diurnal Vertical Migrations

  • Reasons for migration:

  • 1) avoid visual feeding fish in epilimnion by coming up to feed on phytoplankton after dark

  • 2) improve food utilization - filter faster in warmer water, assimilate better in cooler water

Cladoceran cyclomorphosis
Cladoceran Cyclomorphosis

  • Extension of head to form helmet

  • Increase of caudal spine length

  • Caused by increased temperature, turbulence, photoperiod, food

Cladoceran cyclomorphosis1
Cladoceran Cyclomorphosis

  • Advantage of allowing for continued growth of transparent peripheral structures without enlarging central portion of body visible to fish

  • Reduces predation

Food for fish
Food for Fish!

  • Large species favored by many fish (visual and filter-feeders)

  • More energy return from bigger species

  • Eliminates large forms, small ones flourish (big forms often predatory)


  • Microcrustaceans in same size range as cladocerans

  • Several different groups based on differences in body structure

  • 2 major groups: cyclopoids and calanoids


  • Cyclopoids - short 1st antennae


  • Calanoids - long 1st antennae


  • Cyclopoids - most are littoral, but few are open-water planktonic forms

  • All seize food particles and bring them to mouth - raptorial


  • Most are predators (eat zooplankton), but some are herbivores (phytoplankton)

  • Move by swimming with legs


  • Calanoids almost strictly open-water planktonic, seldom in littoral areas

  • Primarily filter feeders on algae, detritus (filtering appendages near mouth - maxillae)

Copepod reproduction
Copepod Reproduction

  • No parthenogensis

  • Both males, females present

  • Sexual reproduction always present

  • Fertilized eggs carried attached to female’s abdomen

Copepod reproduction1
Copepod Reproduction

  • Eggs hatch into nauplius larvae - 3 prs. of legs

  • Grow and molt several times to become copepodite

  • Grow and molt more before becoming adult

Copepod reproduction2
Copepod Reproduction

  • Longer period of time from egg to adult than in rotifers, cladocerans

  • May have resting eggs (overwinter), or diapause in egg or copepodite stage

Community dynamics
Community Dynamics

  • Predation by cyclopoid copepods may kill up to 30% of nauplii or copepodites (of own or other species)

Community dynamics1
Community Dynamics

  • This predation may result in vertical, seasonal separation of similar species

Community dynamics2
Community Dynamics

  • Same diurnal vertical migrations as cladocerans

  • No cyclomorphosis

  • Great as fish food!

Zooplankton generalities
Zooplankton Generalities

  • Assimilation efficiency ~50%

  • Increased with higher temps.

  • Decreased with increased food availability

Zooplankton generalities1
Zooplankton Generalities

  • Highest assimilation when feeding on prime food - right type, size

  • Lower when feeding on bacteria

  • Lowest when feeding on detritus

Zooplankton generalities2
Zooplankton Generalities

  • Seldom evenly distributed

  • Avoidance of shore

  • At mercy of epilimnetic water movements, especially Langmuir spirals

Zooplankton generalities3
Zooplankton Generalities

  • Productivity correlated with phytoplankton production

  • Filter-feeders have higher productivity than predators

Zooplankton generalities4
Zooplankton Generalities

  • Many zooplankton abundant in littoral areas

  • Associated with macrophytes, sediments

  • Abundance related to plant surface area, algal/detrital abundance

Zooplankton generalities5
Zooplankton Generalities

  • Abundance generally highest in spring and fall, lowest in mid-summer

  • Lows correspond with heavy predation by insect larvae, small fish