Zooplankton GrazingZooplankton Grazing

Mechanisms and Impacts on Phytoplankton

Amanda Lee MurbyField Limnology

PBIO/ZOOL 719/819FALL 2005

Grazing: 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.

Predator!Predator!

Grazing: 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 Which are the zooplankton grazers?grazers?

Cladocerans

Copepods

Rotifers

Example:Example: Red Red CalanoidsCalanoids

Cladoceran TypesCladoceran Types

Daphnia ambigua Bosmina longirostris

Calanoids Cyclopoids

Predominantly Herbivores

Predominantly Predators

Copepod TypesCopepod Types

Feeding appendages

Keratella

Rotifer TypesRotifer Types

Kellicottia

Grazing MechanismsGrazing Mechanisms

Filter Feeders

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

Zooplankton do not eat all Zooplankton do not eat all phytoplankton with the phytoplankton with the

same efficiency…same efficiency…

Many algae can avoid being eaten or digested.

Grazers : Grazers : Filter Feeders

Edible particle sizes for filter feeding zooplankton is determined by the mesh width of the filtering apparatus.

Edible Particle SizesEdible Particle Sizes

Lower boundary limits: Particles must fit between setules and third

pair of legs.

-Range from 0.16 to 4.2 m (for Cladocera)

Majority of Daphnia species have an average mesh width of 1.0 m.

Edible Particle SizesEdible 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 m (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 Refer to your handout for the next clip: next clip:

Strategies of Phenotypic Low Strategies of Phenotypic Low Food Adaptations in Food Adaptations in

Daphnia: Filter screens, Daphnia: Filter screens, mesh sizes, and appendage mesh sizes, and appendage

beat rates (ABR)beat rates (ABR)

W. Lampert & H. BrendelbergerW. Lampert & H. Brendelberger(1996)(1996)

Predictions of gain in filtering rate of Predictions of gain in filtering rate of differently sized differently sized DaphniaDaphnia without without

increasing energy costs for pumping increasing energy costs for pumping (ABR)(ABR)

Projected filter area Appendage beat Projected filter area Appendage beat raterate

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

Community grazing ratesCommunity grazing rates

The abundance of herbivorous zooplankton correlated with the community grazing rates.

(Lampert 1988)

Grazing Rate: EquationGrazing 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 SelectivityCoefficient 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.

Clear Water PhaseClear 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 Grazing is directly involved with the Clear Water Phasethe 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)

SummarySummary

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

ReferencesReferences

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?Questions?