Zooplankton

Question 1

define ‘heterotrophic’

Answer 1

dependent on other organisms as food source

Question 2

what are the characteristics of zooplankton?

Answer 2

• Heterotrophic (dependent on other organisms as a food source)
• capable of movement but not against current
• Holoplankton (zooplankton all of its life)
• meroplankton (planktonic only for a period of life cycle)
• Taxonomically and structurally diverse (protista, cnideria, mollusca, arthropoda, chordata, etc.)

Question 3

Zooplankton migrates up to 100-400m vertically every day. Why?

Answer 3

Strong light hypothesis

affected by UV light

-carotenoids protect organisms but makes them more visible -> assume greater risk of predation

shortcomings

• lacks experimental evidence
• go to depths greater than needed to avoid UV light

Surface mixing hypothesis

• allows weak swimming zooplankton to change position
• phytoplankton are patchy and can be grazed out -> migrate into new food source

shortcomings

should not migrate if there is abundant food - evolution favors cheaters

Predation hypothesis

-avoid predators

surface visual predators and migrating nocturnal predators

shortcomings

• daytime depths have sufficient light for predators
• some species migrate deeper than required
• migration possess and use of bioluminescence

in favor

lake studies and predator removal experiments

Energetic hypothesis

(1) phytoplankton production greater with discontinuous grazing
(2) energy savings metabolizing at depth in cooler water

shortcomings

• lacks experimental evidence
• unsure whether savings balance costs of migrating
• assumes warm water increases efficiency of feeding and assimilating food, cool water enhances the efficiency of growth

in favor

strongest vertical migration patterns are seen in the tropics, weakest in polar regions

Question 4

What is the ecological role of zooplankton?

Answer 4

Important trophic link higher level consumers -> many feed on phytoplankton

Regulates phytoplankton biomass

• C2 = C1er-g
• Can drive phytoplankton population to extinction

Nutrient recycling

• Sloppy feeding, excretion
• Promotes primary production

Particle transformers

• Migration
• Faecal pellets & the biological pump

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marine snow -> (carbon loaded) sinks to the bottom

Question 5

What is the most common zooplankton?

Answer 5

Copepods

Best studied, net plankton, hard bodied

Significant grazers of diatoms, dinoflagellates

Ecological significance of small & soft-bodied organisms pretty much unkown

Question 6

Why is there no lag of zooplankton in the North Pacific in Spring?

Answer 6

One generation per year

Water temperature lower at depth (3.8 vs 8.5 deg C), metabolic costs lower, reproduce at depth without feeding

Question 7

What is the significance of copepods in the North Pacific?

Answer 7

Nutrient concentrations > North Atlantic (5 vs 1 mM, Fe limited)

Primary producers dominated by nanoplankton (diatoms/dinoflagellages in North Atlantic) -> abundance of Fe+

Microzooplankton important trophic link to Neocalanus and can keep primary producers in check (high turnover)

Shallow mixed layer in Pacific (100 vs 200 m) autotrophs remain in photic zone

Microzooplankton produce small faecal pellets which do not sink and are mineralised in the water column – no export of nitrogen