Grazing Flashcards
Zooplankton traits
Heterotrophic and planktonic
Impacts of size of grazing
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
What effects mix layer light availability
Surface irradiance – season, latitude, weather
Mix layer depth
Shallow MLD (high light)
Deep MLD (low light)
Particulates – absorb and scatter light, phytoplankton shading
Prey concentration effect on grazing pressure
Ingestion increases as prey concentration increases up to some max
Then it saturates
Trophic Transfer efficiency
Amount of biomass that is moved to next trophic level
10% is fairly average, with 1-20% being common
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)?
1000.15 = 15
150.15 = 2.25
There is 2.25 at third trophic level
Which scenario has the larger bloom (compare values)? Which scenario has the larger winter phytoplankton biomass (compare values)? 80 MLD and 30
MLD
The 80m MLD had the higher bloom (1.3), but the 30m MLD had higher winter values
Compare mixed layer light availability between the two scenarios. Why are wintertime values different? What affects the shape for the 80m scenario?
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
Which scenario has the larger wintertime zooplankton biomass (compare values)? Why are they so different?
The 30m MLD has 10x higher zoop in winter
Far less phytoplankton in winter at 80m MLD so there are less zoop
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?
Just double over and over again in calculator
~100 days
It will reach there in 30+ days
Speculate on the major difference between our two scenarios in terms of what controls the size and timing of the spring bloom.
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
How does phytoplankton size control top level biomass?
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
Copepods traits
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)
Nauplii
Juvenile stage
Crunchy
smaller and weaker swimmers
Less sensory ability
Less successful predators
Copepod Life Cycle
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
What is diapause
Slow respiration in cold deep waters
Advantages of copepod lifecycle timing
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
Importance of diversity of surface migration timing
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
Advantage of planktonic stage for benthic organisms
Promote dispersal with currents to other regions
Euphasiids
Crunchy
1-10cm
Shrimp like
Large phyto and small zoop
Multi-year life cycle
Vertically migrate daily
Advantages of Diel Vertical Migration (DMV)
Avoid predators during the day by staying at depth
Feed at surface during night, when predators cannot see as well
Amphipods
1-10 mm
laterally compressed / flatter than euphausiids
Eats detritus almost exclusively
direct development (no nauplius)
often live commensally within large jellyfish
Ostracods (seed shrimp)
crunchy
~1 mm size
Primary sense – touch (water movement)
Eats large phytoplankton and small
zooplankton
Cladocerans (water fleas)
crunchy
0.2 – 6 mm
Antennae used for swimming
Largely eats detritus
Pteropods (mollusc)
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
Larval gastropods
crunchy
Plankton larvae
Benthic adults
Also look like small snails
thin, dextrally coiled (to the right) calcareous shell
Typically much smaller than local pteropods
Chaetognaths
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
Larvaceans
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
Jellies
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
