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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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zooplankton1
Zooplankton
  • Planktonic animals can be found in almost all animal phyla
  • Most zooplankton belong to 3 major groups: rotifers, Cladocera, and Copepoda
zooplankton2
Zooplankton
  • 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)
rotifers
Rotifers
  • Mostly littoral, sessile, but some are completely planktonic
  • May be dominant zooplankton in some lakes
  • Omnivorous, small (<12 µm)
  • Filter-feeding with corona
rotifers1
Rotifers
  • 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

Brachionus

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
cladocera
Cladocera
  • 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)
cladocera1
Cladocera
  • 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)
copepoda
Copepoda
  • Microcrustaceans in same size range as cladocerans
  • Several different groups based on differences in body structure
  • 2 major groups: cyclopoids and calanoids
copepoda1
Copepoda
  • Cyclopoids - short 1st antennae
copepoda2
Copepoda
  • Calanoids - long 1st antennae
copepoda3
Copepoda
  • Cyclopoids - most are littoral, but few are open-water planktonic forms
  • All seize food particles and bring them to mouth - raptorial
copepoda4
Copepoda
  • Most are predators (eat zooplankton), but some are herbivores (phytoplankton)
  • Move by swimming with legs
copepoda5
Copepoda
  • 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
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