1. Mechanisms and Impacts on Phytoplankton
Zooplankton Grazing
Mechanisms and Impacts on Phytoplankton
Amanda Lee Murby
Field Limnology
PBIO/ZOOL 719/819
FALL 2005

2. Grazing: Terrestrial
Consumption of a portion of a plant’s tissue is most often referred to as Grazing.
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.
Terrestrial grazing usually applies to grasses and other herbaceous vegetation.

3. Predator!

4. 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.

5. Which are the zooplankton grazers?
Cladocerans
Copepods
Rotifers
Example: Red Calanoids

6. Cladoceran Types
Daphnia ambigua
Bosmina longirostris

7. Predominantly Herbivores Predominantly Predators
Copepod Types
Calanoids
Cyclopoids
Feeding appendages
Predominantly Herbivores
Predominantly Predators

8. Rotifer Types
Kellicottia
Keratella

9. Grazing Mechanisms Filter Feeders Raptorial
Nonselective (except for size of food)
Size of prey relatively small
Example: Cladocerans and some Rotifers
Raptorial
Selective (medium-sized particles)
Select on basis of chemical qualities (taste)
Example: Copepods

10. Zooplankton do not eat all phytoplankton with the same efficiency…
Many algae can avoid being eaten or digested.

11. Grazers : Filter Feeders
Edible particle sizes for filter feeding zooplankton is determined by the mesh width of the filtering apparatus.

12. Edible Particle Sizes Lower boundary limits:
Particles must fit between setules and third pair of legs.
-Range from 0.16 to 4.2 mm (for Cladocera)
Majority of Daphnia species have an average mesh width of 1.0 mm.

13. Edible Particle Sizes 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.

14. Refer to your handout for the next clip:

16. Strategies of Phenotypic Low Food Adaptations in Daphnia: Filter screens, mesh sizes, and appendage beat rates (ABR) W. Lampert & H. Brendelberger (1996)

17. Predictions of gain in filtering rate of differently sized Daphnia without increasing energy costs for pumping (ABR)

18. Projected filter area Appendage beat rate

19. Body lengths in correlation with the projected filter areas and with mesh widths.

20. Community grazing rates
The abundance of herbivorous zooplankton correlated with the community grazing rates.
(Lampert 1988)

21. 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.

22. Coefficient of Selectivity
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.

24. 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)

25. Grazing is directly involved with the Clear Water Phase
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)

26. Summary Mesh widths and Edible Particles: upper & lower
Zooplankton grazing applies to the consumption of algae, bacteria, and other planktonic species.
Types: Cladocerans, Copepods, and Rotifers
Grazing mechanisms: Filter-feeder v. Raptorial
Mesh widths and Edible Particles: upper & lower
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.
Community grazing rates and the coefficient of selectivity
Clear Water Phase and impacts on Phytoplankton mortality

27. 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):
Lampert, Winfried. “The Relationship between Zooplankton Biomass and Grazing : A Review”. Limnology (Berlin) – 19(1), (1988):

28. Questions?