Zooplankton communities frequently differ both between different lentic systems, and between different portions of the same system. This exercise will familiarize you with area zooplankton, and compare zooplankton communities within littoral and pelagial areas of a lake.

The zooplankton density and community composition in Lake Goodview or Airport Lake do not differ between littoral and pelagial areas during fall.

Zooplankton will be examined in Lake Goodview or Airport Lake (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 littoral and pelagial zones of the lake.

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.

1) Calculate total numbers of individuals and numbers of each taxon per liter of water for each sample according to the formula:

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 littoral and pelagial zones, 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 littoral and pelagial habitats.

5) Do fish like to eat the kinds of zooplankton that we collected?

Return to Limnology Lab

Neal D. Mundahl
Winona State University
Winona, MN 55987-5838