Transcript c. Life History

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.
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 don’t 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 <2mm)
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
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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
5. Phylum Arthropoda, Class Insecta
Dipteran (true fly) larvae
Chaoborus – voracious predator
-Antennae modified for seizing small zooplankton
-Migrate from benthos <> 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
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)
Filtering Rate
A. Filtering
Cell Density
I=F*D
(D = cell density)
1. Ingestion increases as cells get more dense
2. Curve levels off due to saturation/clogging
Ingestion Rate
B. Ingestion
Cell Density
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II. Zooplankton Feeding
C. Food Concentration and Feeding Rate
Daphnia slows down when
particles are dense
Filtering rate (cm3 animal-1 h-1 )
700
600
500
400
300
200
100
0
0
2
4
6
8
10
12
Particle concentration
(number mL-1)
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4
Filter rate
Ingestion rate
4
3
3
2
2
1
1
0
10
3
10
4
10
5
-3
10
6
Ingestion rate
(number h -1)
800
5
(thousand cells animal-1 h-1)
Particle uptake
Protozoa consumption
levels off
0
Algae (cells cm )
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
COP=Copepod
CLA=Cladoceran (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?
Zooplankton Distribution
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
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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
Piscivores
Planktivores
Zooplankton
Phytoplankton
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