Zooplankton Feeding
231
differences in temperature, (d) varying predation pressure at night versus daylight
conditions (see Exercise 23).
4. How might the concentrations of dissolved oxygen in a stratified lake affect the
rate of clearance. [See Haney (1973).]
5. How might you design an apparatus to measure the rates of clearance and grazing
in situ with natural phytoplankton and zooplankton populations at several depths
in a vertical profile? [See Haney (1971).]
6. Compare your observed clearance rates at different food and zooplankton
concentrations to the observed levels of both in one or more lakes or ponds
studied in Exercises 10 and 11. Assuming that the zooplankton were effective in
their grazing, what impact would you anticipate they would have on
phytoplankton or bacterial growth? Phytoplankton species succession? Why?
7. Zooplankton feed on particles. During maceration and digestion offood particles,
much of the food is lost as fragments, leaching of soluble organic matter, and
incompletely digested food material. What is the fate of this partially utilized
food in the lake ecosystem? Describe in detail.
8. How might inorganic nutrients (such as phosphorus) of the food, released during
the ingestion process, affect the phytoplankton and/or bacterioplankton?
9. How effective is the grazing by rotifers compared to that of cladocerans? Copepods
to cladocerans?
10. How would you expect clearance rates of the same species to change with
increasing body length? Increasing environmental temperatures?
11. How would you anticipate clearance efficiency to change with size of food
particles? With increasing food concentrations? [See Lehman (1976).]
PROTOZOAN FEEDING RATES
1. Obtain a bacterial enrichment by adding filtered lake water and a grain of rice to
a culture flask. After a few days of growth, inoculate this culture with ciliated
protozoa and allow several additional days for growth of the ciliates.
2. Pour the culture through Nitex netting of 30- to 100-j1m mesh in accordance with
the size of the protozoa. This procedure simply removes large particles and clumps
of bacteria.
3. Take a preliminary bacterial sample and enumerate the microorganisms (see
Exercise 19). Make a fluorescent microsphere standard by adding a drop of the
stock solution of micro spheres (recommended sizes between 0.5 and 1.0 j1m) to
10 ml of filtered lake water. Sonicate the standard to disperse the microspheres, if
possible, and take a subsample for enumerating by the same procedure as was
used for bacteria except omitting the use of acridine orange stain. Add fluorescent
micro spheres from the standard to the culture at a concentration of about 10%
of the bacterial density (Pace and Bailiff, 1987).
4. Immediately take a 5- to lO-ml subsample and preserve with formalin solution to
yield a final concentration of 1 to 2%.
5. Continue taking subsamples at 10-min intervals for 1 h. Keep careful track of
the time of the experiment and the actual time that the subsamples were killed
to stop feeding.
6. Filter subsamples with gentle vacuum « 100mm Hg) through 2- or 5-j1m pore
size Irgalan black-stained polycarbonate filters. Sandwich each filter between drops
of nonfluorescent immersion oil (e.g., Cargille Type A) and cover with a cover slip.
231
differences in temperature, (d) varying predation pressure at night versus daylight
conditions (see Exercise 23).
4. How might the concentrations of dissolved oxygen in a stratified lake affect the
rate of clearance. [See Haney (1973).]
5. How might you design an apparatus to measure the rates of clearance and grazing
in situ with natural phytoplankton and zooplankton populations at several depths
in a vertical profile? [See Haney (1971).]
6. Compare your observed clearance rates at different food and zooplankton
concentrations to the observed levels of both in one or more lakes or ponds
studied in Exercises 10 and 11. Assuming that the zooplankton were effective in
their grazing, what impact would you anticipate they would have on
phytoplankton or bacterial growth? Phytoplankton species succession? Why?
7. Zooplankton feed on particles. During maceration and digestion offood particles,
much of the food is lost as fragments, leaching of soluble organic matter, and
incompletely digested food material. What is the fate of this partially utilized
food in the lake ecosystem? Describe in detail.
8. How might inorganic nutrients (such as phosphorus) of the food, released during
the ingestion process, affect the phytoplankton and/or bacterioplankton?
9. How effective is the grazing by rotifers compared to that of cladocerans? Copepods
to cladocerans?
10. How would you expect clearance rates of the same species to change with
increasing body length? Increasing environmental temperatures?
11. How would you anticipate clearance efficiency to change with size of food
particles? With increasing food concentrations? [See Lehman (1976).]
PROTOZOAN FEEDING RATES
1. Obtain a bacterial enrichment by adding filtered lake water and a grain of rice to
a culture flask. After a few days of growth, inoculate this culture with ciliated
protozoa and allow several additional days for growth of the ciliates.
2. Pour the culture through Nitex netting of 30- to 100-j1m mesh in accordance with
the size of the protozoa. This procedure simply removes large particles and clumps
of bacteria.
3. Take a preliminary bacterial sample and enumerate the microorganisms (see
Exercise 19). Make a fluorescent microsphere standard by adding a drop of the
stock solution of micro spheres (recommended sizes between 0.5 and 1.0 j1m) to
10 ml of filtered lake water. Sonicate the standard to disperse the microspheres, if
possible, and take a subsample for enumerating by the same procedure as was
used for bacteria except omitting the use of acridine orange stain. Add fluorescent
micro spheres from the standard to the culture at a concentration of about 10%
of the bacterial density (Pace and Bailiff, 1987).
4. Immediately take a 5- to lO-ml subsample and preserve with formalin solution to
yield a final concentration of 1 to 2%.
5. Continue taking subsamples at 10-min intervals for 1 h. Keep careful track of
the time of the experiment and the actual time that the subsamples were killed
to stop feeding.
6. Filter subsamples with gentle vacuum « 100mm Hg) through 2- or 5-j1m pore
size Irgalan black-stained polycarbonate filters. Sandwich each filter between drops
of nonfluorescent immersion oil (e.g., Cargille Type A) and cover with a cover slip.