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Lec 8: Zooplankton

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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Lec 8: Zooplankton

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  1. 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 1

  2. 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.

  3. I. Major Types of Zooplankton: Qualitative Distribution Small Large Substrate-Free Space 2

  4. 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 3

  5. 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 4

  6. 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 5

  7. 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) 6

  8. 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 7

  9. 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 8

  10. 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

  11. 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 10

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  13. 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 12

  14. 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 13

  15. 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 14

  16. II. Zooplankton Feeding: E. Mechanics Movie 18

  17. Filtering Rate Cell Density 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 15

  18. ) 5 -1 h -1 4 animal 3 3 2 Filtering rate (cm 1 0 3 4 5 6 10 10 10 10 -3 -1 ) Algae (cells cm ) (number mL II. Zooplankton Feeding C. Food Concentration and Feeding Rate Daphnia slows down when particles are dense Protozoa consumption levels off 4 Filter rate Ingestion rate 800 3 700 ) -1 Particle uptake 600 Ingestion rate (thousand cells animal 500 2 (number h 400 300 1 200 -1 h 100 -1 ) 0 0 2 4 6 8 10 12 14 0 Particle concentration The predator feeding response to prey concentration is…..? 16

  19. 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? 17

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  21. 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 20

  22. 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 21

  23. 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 22

  24. III. Zooplankton Ecology B. Community Ecology Source of this figure? What factors explain these patterns? 23

  25. Conceptual Diagram of Trophic Cascade 24

  26. III. Zooplankton Ecology Piscivores Planktivores Zooplankton Phytoplankton C. Interactions between Planktivorous fish, Zooplankton, Phytoplankton 25

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