Lec 8: Zooplankton I. Major Types of Zooplankton -Taxonomy, Reproduction, Feeding II. Comparative Zooplankton Feeding -Particle size selection -Size.

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

Substrate-FreeSpace

Small

Large

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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 GroupsA. Kingdom Protista (microzooplankton)

-single celled eukaryotes-based on form of movement

1. Taxonomya. Mastigophora (flagellates) -Probably no sexual reproduction

b. Sarcodina (amoeboid forms) -Amoeba (Naked) -Difflugia (Case of sand grains; Theca)

c. Ciliophora (ciliates) -Very diverse

-Paramecium

I. Major Types of Zooplankton: Origins

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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

A. Kingdom Protista

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B. Kingdom Animalia (metazoans)

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

I. Major Types of Zooplankton; A. Taxonomic Groups

Brachionus

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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)

1. Phylum Rotifera (Rotatoria)

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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 9

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 topredation 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 asexual13

5. Phylum Arthropoda, Class InsectaDipteran (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

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Cons by LMB

II. Zooplankton Feeding: E. Mechanics

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Movie

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

Cell Density

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Cell DensityIn

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Rat

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Protozoa consumptionlevels off

Daphnia slows down when particles are dense

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Particle concentration (number mL-1)

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ticle

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103 104 105 106

Algae (cells cm-3

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cm3 a

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Ingestion rate

(thousand cells animal -1 h

-1)

Filter rateIngestion rate

II. Zooplankton Feeding C. Food Concentration and Feeding Rate

The predator feeding response to prey concentration is…..?16

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=CopepodCLA=Cladoceran (e.g. Daphnia)

Habitat Adaptations? 17

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II. Zooplankton FeedingF. 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 phytoplankton6. Influence of size-selective

predation on zooplankton

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III. Zooplankton EcologyA. Avoiding Predation

1. Mechanicala. Size (too small or too large)

b. Spines (chemical cues may induce protection)

-Cyclomorphosis

2. Chemical (mostly w/ respect to phytoplankton)a. Toxinsb. Poor quality

3. Behavioral a. Coloration b. Escape

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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

III. Zooplankton Ecology: Predation Escape

Zooplankton Distribution

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Source of this figure?

What factors explainthese patterns?

III. Zooplankton Ecology B. Community

Ecology

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Conceptual Diagram of Trophic Cascade

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C. Interactions between Planktivorous fish, Zooplankton, Phytoplankton

Piscivores

Planktivores

Zooplankton

Phytoplankton

III. Zooplankton Ecology

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