Lec 8: Zooplankton

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Lec 8 Zooplankton
I. Major Types of Zooplankton -Taxonomy,
Reproduction, Feeding II. Comparative
Zooplankton Feeding -Particle size
selection -Size efficiency hypothesis III.
Zooplankton Ecology -Factors affecting
assemblages (Predation) -Foodwebs and community
ecology of lakes
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Multicellular Freshwater Animals, Invertebrates

• Porifera- sponges
• Cnideria- include hydra
• Platyhelminthes- include planarians
  (Turbelleria)
• Gastrotricha- can be abundant, benthic
• Rotifera- rotifers some sexual, others asexual
• Nematoda- important predators and bactivores
• Mollusca- Gastropoda (snails and limpets) and
  Bivalva (clams and mussels)
• Annelida- segmented worms
• Bryozoa- sessile ciliated invertebrates
• Arthropoda- includes insects, crustacea, etc.

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I. Major Types of Zooplankton Qualitative
Distribution
Small Large
Substrate-Free Space
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I. Major Types of Zooplankton Origins
Most zooplankton are derived from marine
ancestors (only aquatic spiders, mites, insects,
pulmonate gastropods, rotifers and perhaps
cladocera are not derived directly from the sea)
Taxonomic Groups A. Kingdom Protista
(microzooplankton) -single celled
eukaryotes -based on form of movement
1. Taxonomy a. Mastigophora (flagellates)
-Probably no sexual reproduction b.
Sarcodina (amoeboid forms)
-Amoeba (Naked) -Difflugia
(Case of sand grains Theca) c. Ciliophora
(ciliates) -Very diverse
-Paramecium
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A. Kingdom Protista
2. Miscellaneous a. Less work done on
the ecology of individual microzooplankton
protists than other groups of zooplankton 3.
Life history a. Reproduction by
conjugation b. Some can reproduce
asexually by fision c. Many forms can
produce resistant protective cysts induced by
drying, excessive heat or cold, lack of food
4. Feeding a. Mastigophora consume
small algae, bacteria and detritus b.
Ciliophora and Sarcodina can also consume
Mastigophora c. Cilia and flagella are
used both for motility and to set up currents
to bring food to the cell d. Sarcodina
have pseudopodia that engulf food e.
Are eaten by other zooplankton
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I. Major Types of Zooplankton A. Taxonomic
Groups
B. Kingdom Animalia (metazoans)
Brachionus
1. Phylum Rotifera (Rotatoria) a. Taxonomy
i. Class Bdellioda (a) 200
species very difficult to tell apart
(b) ID them by their trophi (jaws) ii.
Class Monogonata (a) 90 of the
species (b) Representative genera
Asplanchna
Keratella Filinia
Conochilus
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1. Phylum Rotifera (Rotatoria)
b. Miscellaneous i. Small 30 mm
(include the smallest metazoan) in tropics to 1
mm ii. Most morphologically diverse
group of freshwater plankton iii. Some
species are sessile (attached), but many are
purely planktonic iv. Most abundant in
freshwater (95 of 2000spp) evolved in
freshwater v. Have eutely cell
constancy no cell division in any somatic cells
vi. Cilia band is known as a corona
vii. Jaws are called trophi and are made of
chitin viii. Often fairly abundant
(200-300/L up to 5000/L) c. Life History
i. Bdelloid males are never seen (no sex for
40 million years) ii. Monogonata Males
dont eat are haploid -Only 1-2 Mictic
generations / yr (meiosis w/ egg
sperm) -Mostly (20-40 gen) Amictic diploid
eggs, asexual d. Feeding i. The
rotifers use their cilia to create currents
around their anterior ends ii. Some are
predatory some eat algae some eat protozoans
iii. Trophi (jaws)
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2. Phylum Arthropoda, Class Crustacea, Order
Branchiopoda a. Taxonomy i.
Cladocera (examples) (a) Daphnia
water flea (b) Bosmina
(c) Leptodora b. Miscellaneous
i. 300 ?m to 1 cm long ii. Have
a bivalve carapace with a gap iii.
Herbivorous cladocera have paddle-shaped legs and
draw water currents into carapace 2nd
antennae are for swimming c. Feeding
i. Most are herbivorous ii. Some
predaceous (Leptodora, Polyphemus) iii.
Some can feed on bacteria
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d. Life History i. Rapid life cycles - 1
to 2 weeks per generation ii. Most often
are parthenogenic (favorable periods)
iii. Direct development - no distinctive change
in morphology associated with each instar
(unlike most other crustaceans) iv.
Clutch size variable a. related to
age (body size), instar, food levels
b. eggs produced after each adult molt
v. Cues for male and haploid egg production
crowding (excretion products),
decreased food, light decreases, temperature
decreases
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3. Phylum Arthropoda, Class Crustacea, Order
Copepoda a. Taxonomy i. Suborder
Cyclopoida short antennae -Mesocyclops
2 egg sacs ii. Suborder Calanoida
long antennae -Diaptomus 1
egg sac iii. Suborder Harpacticoida --
mostly littoral and benthic some parasitic
b. Miscellaneous i. Widely
distributed in all freshwaters (a)
From tropical to arctic regions (b)
From low ionic strength to salty ii.
Body size -- 300 ?m to 5 mm (most lt2mm)
iii. Three groups distinguished based on
-Body shape, Antennae length, egg sacs
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c. Life History i. Sexual reproduction
only males and females ii. Egg
development temperature dependent iii.
Indirect development (not suited to temporary
conditions) (a) juvenile nauplius
(7 stages) (b) copepodid stage (6
stages) metamorphosis to this stage
Cyclopoida (a) Eggs are
carried by the females in egg sacs (b)
Relatively short generation time, several per
year 1-2 months per
generation (c) Resting stages
-In some species the eggs can be dried
and hatch when wet -Diapause in
copepodite IV stage, not as a resting egg
Calanoida (a) Relatively longer generation
time, several per year? (b) Most
carry eggs in a sac or deposit them into water
(c) No diapause stage as a copepodite
(d) Production of morphologically
distinct resting eggs
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d. Feeding i. Cyclopoida
(a) Predaceous/omnivorous -Can
feed on algae or other animals
-Nauplii (juveniles) are generally herbivorous
and there is an ontogenetic (developmental)
switch from herbivory to predation as they
metamorphose to adult copepods (b)
No elaborate modifications for feeding
ii. Calanoida (a) Set up feeding
currents and remove particles can select their
food (b) Mostly herbivorous large
forms like Epischura are sometimes
predaceous (but are herbivorous as nauplii)
(c) Mouthparts of some modified for
filter-feeding iii. How do they find
food? (a) Mechanoreception setae
on antennae (b) Chemoreception

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4. Phylum Arthropoda, Class Crustacea, Other
Crustacea a. Order Malacostraca i.
Mysidacea - Mysids -Glacial
relicts, Long lived, Predatory/omnivores, Open
Water -Sensitive to low DO, introduced as fish
forage ii. Amphipoda
-Life history two sexes long lived
-Feeding - omnivores, bottom detritus b.
Order Eubranchiopoda In temporary bodies
of water without fish Eat algae, bacteria,
protozoans, rotifers, detritus Have
resting eggs i. Anostraca - Fairy
shrimp -Swim on backs (like tiny
walruses), UC-Merced? ii.
Notostraca tadpole shrimp (Triops)
-will also eat dead animals or are sometimes
predaceous c. Order Ostracoda
-Mostly benthic, Herbivorous, Resting eggs,
Sexual or asexual
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5. Phylum Arthropoda, Class Insecta Dipteran
(true fly) larvae Chaoborus
voracious predator -Antennae modified for
seizing small zooplankton -Migrate from
benthos ltgt open water -May or may
not coexist w/ fish -Can influence
zooplankton assemblages in absence of fish
-Long generation time
Cons by LMB
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II. Zooplankton Feeding E. Mechanics
Movie
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II. Zooplankton Feeding A. Filtering
1. Volume of water cleared per animal per time
(F) versus density of food (D) 2. F
filtering rate or clearance rate 3.
Decreases at high cell density because
filtering apparatus clogs 4. Increased
filtering rate for larger zooplankton
(especially Daphnia) B. Ingestion I F
D (D cell density)
1. Ingestion increases as cells get more dense
2. Curve levels off due to
saturation/clogging
Ingestion Rate
Cell Density
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II. Zooplankton Feeding C. Food Concentration
and Feeding Rate
Daphnia slows down when particles are dense
Protozoa consumption levels off
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Filter rate
Ingestion rate
800
3
700
)
-1
600
Particle uptake
Ingestion rate
(thousand cells animal
500
2
(number h
400
300
1
200
-1
h
100
-1
)
0
0
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8
10
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0
Particle concentration
The predator feeding response to prey
concentration is..?
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D. Differences in selectivity between different
zooplankton grazers 1. Copepods more
selective than cladocera 2.
Herbivorous calanoid copepods do better at low
food quantities and low food qualities than
Daphnia
COPCopepod CLACladoceran (e.g. Daphnia)
Habitat Adaptations?
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II. Zooplankton Feeding F. Size Efficiency
Hypothesis 1. Herbivorous zooplankton are
food collectors (Type 1 F.R.) 2.
Competition for food (1-15um) 3. Size-based
food collection efficiency (Food
collecting surfaces? body length2) 4. Negative
relationship of size and mass-specific
metabolic demand 5. Effects on
phytoplankton 6. Influence of
size-selective predation on zooplankton
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III. Zooplankton Ecology A. Avoiding Predation
1. Mechanical a. Size (too small or too large) b.
Spines (chemical cues may induce
protection) -Cyclomorphosis 2. Chemical (mostly
w/ respect to phytoplankton) a. Toxins b. Poor
quality 3. Behavioral a. Coloration
b. Escape
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III. Zooplankton Ecology Predation Escape
Diel Vertical Migration - DVM 1. What is
DVM? 2. Cues to movement a. Light b.
Chemical cues Fish Odor 3.
Possible Adaptive Value a. Predation b.
Energetics - changed metabolic rates c.
Avoidance of UV radiation d. Food quality
Zooplankton Distribution
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III. Zooplankton Ecology B.
Community Ecology
Source of this figure? What factors
explain these patterns?
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Conceptual Diagram of Trophic Cascade
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III. Zooplankton Ecology
C. Interactions between Planktivorous
fish, Zooplankton, Phytoplankton
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