Transcript Zooplankton Grazing on Phytoplankton

Zooplankton Grazing
Mechanisms and Impacts
on Phytoplankton
Amanda Lee Murby
Field Limnology
PBIO/ZOOL 719/819
FALL 2005
Grazing: Terrestrial

Consumption of a portion of a plant’s tissue is most
often referred to as Grazing.
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Herbivores eat whole plants or parts of plants.
Functioning as a Predator = Consumption of entire plant.
Functioning as a Parasite = Consumption of tissue, but without
killing plant.
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Terrestrial grazing usually applies to grasses and other
herbaceous vegetation.
Predator!
Grazing: Aquatic (Plankton)

Grazing refers to the predator- prey interactions in
water where algae and bacteria are the prey organisms.

Filtering is an example of grazing in the aquatic world; removal
of algae or the portion of water volume that is (ideally) cleaned
of particles.

Aquatic grazing usually applies to algae, bacteria, and
other plankton.
Which are the zooplankton
grazers?
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Cladocerans
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Copepods
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Rotifers
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Example: Red
Calanoids
Cladoceran Types
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Daphnia ambigua
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Bosmina longirostris
Copepod Types
Calanoids
Cyclopoids
Feeding appendages
Predominantly
Herbivores
Predominantly
Predators
Rotifer Types
Kellicottia
Keratella
Grazing Mechanisms
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Filter Feeders
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Nonselective (except for
size of food)
Size of prey relatively
small
Example: Cladocerans
and some Rotifers

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Raptorial
Selective (mediumsized particles)
 Select on basis of
chemical qualities
(taste)
 Example: Copepods
Zooplankton do not eat all
phytoplankton with the
same efficiency…
Many algae can avoid being
eaten or digested.
Grazers : Filter Feeders

Edible particle sizes for
filter feeding
zooplankton is
determined by the mesh
width of the filtering
apparatus.
Edible Particle Sizes
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Lower boundary limits:

Particles must fit between setules and third
pair of legs.
-Range from 0.16 to 4.2 mm (for Cladocera)
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Majority of Daphnia species have an average
mesh width of 1.0 mm.
Edible Particle Sizes
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Upper boundary limits:
Particles determined by the opening of the
mandibles and/or the opening of the
carapace gape.
-Range from 20 to 50 mm (for Cladocera)
 Particles that exceed the upper size limit can
be broken if fragile or are protected from
Cladocera…
 Copepods generally eat these larger particles.
Refer to your handout for the
next clip:
Strategies of Phenotypic Low
Food Adaptations in Daphnia:
Filter screens, mesh sizes, and
appendage beat rates (ABR)
W. Lampert & H. Brendelberger
(1996)
Predictions of gain in filtering rate of
differently sized Daphnia without
increasing energy costs for pumping
(ABR)
Projected filter area
Appendage beat rate
Body lengths in correlation with the projected
filter areas and with mesh widths.
Community grazing rates

The abundance of
herbivorous
zooplankton
correlated with the
community grazing
rates.
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(Lampert 1988)
Grazing Rate: Equation

y = Gw
Grazing rates (y) are
estimated from the
filtering rate of the total
zooplankton community
(G) and the coefficient
of selectivity (w) for the
specific algae that is
being considered.
Coefficient of Selectivity
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Phytoplankton can avoid mortality.
wi = yi/ yopt
.
The Selection Coefficient expresses lower
mortality, compared to optimally eaten
species.
* Not a fixed Characteristic for a particular species.
Clear Water Phase
“Describes the very regular occurrence of a
minimum density of phytoplankton in the
middle of the growth period (North temperate
latitudes usually in May-June). Most
frequently in meso- and eutrophic lakes”.
(Lampert and Sommers 1997)
Grazing is directly involved with the
Clear Water Phase
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During the clear water
phase (usually Spring),
a large amount of
herbivorous
zooplankton will occur.
Zooplankton grazing is
a major cause of
phytoplankton mortality.
(Lampert and Sommers
1997)
Summary
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Zooplankton grazing applies to the consumption of algae, bacteria, and
other planktonic species.
Types: Cladocerans, Copepods, and Rotifers
Grazing mechanisms: Filter-feeder v. Raptorial
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Mesh widths and Edible Particles: upper & lower
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Filtrations rates correlate with body size
 More food is collected at low particle concentrations (and is more
efficient) by increasing maximum filtering rate by enlarging its
filter screens than by increasing ABR.
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Community grazing rates and the coefficient of selectivity
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Clear Water Phase and impacts on Phytoplankton mortality
References
Lampert, Sommers. Limnoecology: The Ecology of Lakes and
Streams. Oxford University Press. 1997
Ricklefs, R.E. The Economy of Nature (fifth Ed.) WH Freeman and
Company New York. 2001
Lampert, Brendelberger. “Strategies of Phenotypic Low Food
Adaptation in Daphnia: Filter screens, mesh sizes, and appendage beat
rates”. Limnology. Oceanography – 41(2), (1996): 216-223.
Lampert, Winfried. “The Relationship between Zooplankton Biomass
and Grazing : A Review”. Limnology (Berlin) – 19(1), (1988): 11-20.
Questions?