Teachers Resources

Host and Substrate Demonstration

This demonstration simulates the need for the proper host and appropriate substrate for the survival of a freshwater mussel. The simulation will be done twice. Once as the glochidia of a common mussel, the giant floater, and again as glochidia of the endangered Higgins' eye pearlymussel.

The glochidia of a giant floater can develop to maturity on a variety of fish host species. It can also can live on many different substrates.

The Higgins' eye pearlymussel is host-specific. This means that as a glochidium it can only develop on walleye and sauger. Higgins' eye also survive best when living in strong current areas of the Mississippi. Current is one factor that determines what type of substrate is found in an area. In the case of Higgins' eyes, they survive best on the following substrates: gravel, sand and gravel, and sand.

The following playing cards will need to be made (number of cards needed is indicated in parentheses if more than one). Pictures or text can be used to identify these cards. The cards should be at least 6 X 9 inches in size.

1. Place the cards face down in a large play area with host cards at one end and substrate cards at the other.
   
2. Have students line up behind the end with the substrate cards and tell them that they are glochidia of giant floaters, a common species of mussel (during the second round, they will be Higgins' eye). Instruct them that they will now find out what species of fish they have infected by walking to the other end of the playing field and stepping on one of the fish host cards. More than one student can be on a card at once. Tell them to wait until told to turn over the host cards.
   
3. After each student has placed a foot on the host card, have them pick up that card to see which species of fish they have attached to. Since giant floaters can successfully develop to maturity on a variety of species, all students will "survive."
   
4. Have them place the cards face down on the ground.
   
5. Now find out what type of substrate their fish is over when they detach from their host. Instruct the students to walk to the other end of the playing field and step on one of the substrate cards. More than one student can be on a card at once. Tell them to wait until told to turn over the substrate cards.
   
6. Inform the students who have landed on a "sand bar that dries up in the summer" or "riprap" that they did not survive. All other students will survive. Students that landed on a sand bar that dries up in the summer did not survive because mussels, especially very small mussels, will not be able to move into deeper water as the sandbar is exposed. Students that landed on riprap did not survive because chances of a mussel surviving on riprap is slim because of the size of the rock and numerous crevices among the rocks. This limits their growth and feeding potential and usually results in mortality.
   
7. Repeat the simulation, this time have the students be Higgins' eye mussels. Make the following changes to reflect limiting factors for Higgins' eye mussels.

In Step 3, only students that chose walleye or sauger will survive and proceed to the substrate stage. All other students have infected a fish species on which they cannot survive.

In Step 6, students that land on a "sand bar that dries up in the summer" or "riprap" do not survive for the same reasons previously stated. Additionally, Higgins' eye glochidia that land on "backwater muck" do not survive. Higgins' eye survive best in areas of the Mississippi having strong currents. "Backwater muck" is found in areas lacking current. Current is one factor that determines what type of substrate is found in an area. In the case of Higgins' eyes, they survive best on the following substrates: gravel, sand and gravel, and sand.

Assessment

Have student write two reasons why the freshwater mussel's life cycle or feeding habits make them sensitive to changes in their habitats caused by humans.

Extension

Have the students research the fish species listed above and determine their habitat requirements. Then have them make the fish and substrate cards as part of the preparation for this activity.