Winona
State University
BIOL 415/527 – ECOLOGY OF LARGE RIVERS
LAB EXERCISE #8
ZOOPLANKTON COMMUNITY ANALYSES
OBJECTIVE
Zooplankton communities frequently differ both between different river systems,
and between different portions of the same system. This exercise will
familiarize you with area zooplankton, and compare
zooplankton communities within a channel and backwater habitat in the
Mississippi River.
HYPOTHESIS
The zooplankton density and community composition in the Mississippi River will
differ significantly between channel and backwater habitats during fall.
METHODOLOGY
Zooplankton will be examined in a secondary channel and a backwater (hopefully
during a beautiful fall day). The following describes the general procedure we
will follow to examine the hypothesis listed above.
Field collections:
Zooplankton will be collected with a standard plankton net. The net is a
traditional conical mesh net with a spigot tail. The net can be drawn either
horizontally or vertically through the water, and the volume sampled determined
by knowing the area of the net mouth and the length of the water column through
which it was drawn.
1) Collect zooplankton samples from the lake by lowering the net to near the
bottom and drawing it back toward the surface.
2) Wash zooplankton from the sides of the net down into the spigot and flush
the contents of the spigot into a collecting jar. Record the length of the
water column sampled and add formalin preservative to the sample.
3) Repeat the above procedure until three collections have been made in both channel
and backwater zones of the river.
Laboratory processing:
1) Adjust the contents of each sample jar to a known volume by adding or
removing water. It is convenient to adjust the volume such that each ml of
sample is equivalent to some whole integer of liters of water strained. The
degree to which the sample is concentrated will depend on the density of organisms
in the water.
2) Once sample volume has been adjusted, shake the sample thoroughly and then
quickly remove a 1-ml subsample with a Hensen-Stempel
pipet.
3) Transfer the contents of the pipet to a 1-ml Sedgwick-Rafter counting cell,
place a cover slip over the cell, and examine under a compound microscope,
using the scanning objective. The low-power objective may be used to facilitate
identification of specific organisms, but DO NOT ATTEMPT TO USE ANY
HIGHER MAGNIFICATION. Attempts to do so will result in breaking the cover
slip.
4) Using the picture keys provided, identify and count
the number of individuals of each taxon within the entire counting cell.
ANALYSIS
1) Calculate total numbers of individuals and numbers of each taxon per liter
of water for each sample according to the formula:
# per liter =
# in counting cell X ml of plankton concentrate
liters of water concentrated
2) Use
data from other class members to generate a mean # per liter for
each sample.
3) Compare the numbers and types of taxa collected from channel and backwater
habitats, and make note of differences in abundance if the same taxon occurs in
both habitats.
4) Use t-tests to compare total zooplankton densities, as well as densities of
the various taxa (e.g., cladocerans, copepods,
rotifers), between channel and backwater habitats.
EQUIPMENT
Plankton net
Collecting jars
Wash bottles
Formalin
Pipettes
Graduated cylinders
Microscopes
Slides/coverslips
Boats/associated gear
Meter sticks
Return to ELR lab
Neal D. Mundahl
Winona State University
Winona, MN 55987-5838