Grazing

Question 1

Zooplankton traits

Answer 1

Heterotrophic and planktonic

Question 2

Impacts of size of grazing

Answer 2

Bigger zooplankton graze larger phytoplankton – this has a positive relationship but group dependent

Larger zooplankton more complex so they can be more selective

Prey niches depending on size

Larger are more motile

Larger zooplankton more complicated reproduction, slower reproduction

Question 3

What effects mix layer light availability

Answer 3

Surface irradiance – season, latitude, weather

Mix layer depth
Shallow MLD (high light)
Deep MLD (low light)

Particulates – absorb and scatter light, phytoplankton shading

Question 4

Prey concentration effect on grazing pressure

Answer 4

Ingestion increases as prey concentration increases up to some max

Then it saturates

Question 5

Trophic Transfer efficiency

Answer 5

Amount of biomass that is moved to next trophic level

10% is fairly average, with 1-20% being common

Question 6

Suppose a primary production rate of 100 mmol C m-2 d-1 and a trophic transfer efficiency of 15%. What production can you expect at the third trophic level (secondary consumer)?

Answer 6

1000.15 = 15
150.15 = 2.25

There is 2.25 at third trophic level

Question 7

Which scenario has the larger bloom (compare values)? Which scenario has the larger winter phytoplankton biomass (compare values)? 80 MLD and 30
MLD

Answer 7

The 80m MLD had the higher bloom (1.3), but the 30m MLD had higher winter values

Question 8

Compare mixed layer light availability between the two scenarios. Why are wintertime values different? What affects the shape for the 80m scenario?

Answer 8

There is more winter light available at 30m because MLD is shallower, spend more time near surface.

Phytoplankton bloom shades and reduces the light availble

Question 9

Which scenario has the larger wintertime zooplankton biomass (compare values)? Why are they so different?

Answer 9

The 30m MLD has 10x higher zoop in winter

Far less phytoplankton in winter at 80m MLD so there are less zoop

Question 10

Imagine zooplankton with a growth rate of 0.1 d-1 (1 doubling every 10 days). How long would it take a zooplankton population biomass starting at 0.0001 uM-N to reach 0.1 uM-N?

What about a population starting at 0.01 uM-N?

Answer 10

Just double over and over again in calculator

~100 days

It will reach there in 30+ days

Question 11

Speculate on the major difference between our two scenarios in terms of what controls the size and timing of the spring bloom.

Answer 11

Wintertime light availability controls spring time grazing limitation

Low light levels in winter reduces zooplankton to very low values

High winter light – larger phytoplankton population & larger zooplankton population
So larger initial zooplankton population grows more quickly to exert top-down control on phytoplankton

Question 12

How does phytoplankton size control top level biomass?

Answer 12

Smaller phytoplankton go through more trophic levels to reach the top level

Loss of biomass at each trophic level – trophic transfer efficiency
This means less top-level biomass

Small phytoplankton grow in. nutrient-poor waters so there is a lower phytoplankton biomass to begin with

Question 13

Copepods traits

Answer 13

Crunchy
Very abundant (~80%)
Eat large phyto and small zoop
key trophic link
0.1-5mm
Sexual
Generation time several weeks to several years (species and environment dependent)

Question 14

Nauplii

Answer 14

Juvenile stage
Crunchy
smaller and weaker swimmers
Less sensory ability
Less successful predators

Question 15

Copepod Life Cycle

Answer 15

Adults spend winter/fall at depth resting

Produce eggs during early spring, so nauplii coincide with bloom of phytoplankton

Juvenile stages grow and feed during spring/summer

Question 16

What is diapause

Answer 16

Slow respiration in cold deep waters

Question 17

Advantages of copepod lifecycle timing

Answer 17

Nauplii hatch when phytoplankton levels are very high, helps with poor feeding of larval stages

Adults slow respiration and avoid predation when food is scarce

Question 18

Importance of diversity of surface migration timing

Answer 18

Phytoplankton bloom timing is variable depending on environmental conditions

Have some migrate earlier and some later, so that a group will always coincide with the bloom timing

Makes sure some amount is successful every year

Question 19

Advantage of planktonic stage for benthic organisms

Answer 19

Promote dispersal with currents to other regions

Question 20

Euphasiids

Answer 20

Crunchy
1-10cm
Shrimp like
Large phyto and small zoop
Multi-year life cycle
Vertically migrate daily

Question 21

Advantages of Diel Vertical Migration (DMV)

Answer 21

Avoid predators during the day by staying at depth

Feed at surface during night, when predators cannot see as well

Question 22

Amphipods

Answer 22

1-10 mm
laterally compressed / flatter than euphausiids
Eats detritus almost exclusively
direct development (no nauplius)
often live commensally within large jellyfish

Question 23

Ostracods (seed shrimp)

Answer 23

crunchy
~1 mm size
Primary sense – touch (water movement)
Eats large phytoplankton and small
zooplankton

Question 24

Cladocerans (water fleas)

Answer 24

crunchy
0.2 – 6 mm
Antennae used for swimming
Largely eats detritus

Question 25

Pteropods (mollusc)

Answer 25

crunchy
Spend full life as plankton
look like small snails
foot has evolved into paired wings for swimming.
Most common in our samples Limacina spp.
thin, sinistrally coiled (to the left) calcareous shell
few mm → 30mm
feeds by secreting a sticky mucus web

Question 26

Larval gastropods

Answer 26

crunchy
Plankton larvae
Benthic adults
Also look like small snails
thin, dextrally coiled (to the right) calcareous shell
Typically much smaller than local pteropods

Question 27

Chaetognaths

Answer 27

soft
5mm – 10 cm
Carnivorous raptorial feeders
Attack plankton several times their own size
hang motionless until prey detected
use spines and hooks to grab prey
diel vertical migrators
Hermaphroditic

Question 28

Larvaceans

Answer 28

soft
Looks like a small tadpole
2-10mm in length
Secretes a mucous “house” through which
water is pumped. Food particles sieved out
When filter clogs, house abandoned and
new one secreted
Old “houses” are important food source
for other zooplankton and bacteria

Question 29

Jellies

Answer 29

soft
diverse collection of species from
several different phyla:
Cnidarians (i.e. true jellyfish) and
Ctenophores (i.e. comb jellies)
both “fish” for smaller
zooplankton with tentacles
Salps (primitive chordates) are
filter feeders that form dense
patches