Snails: Population Calculation in an Aquatic Environment
In this activity students will be doing primarily two things. First, they will collect and examine aquatic snails. They will identify the parts of a snail as well as determine the number of species present in the environment. The second task is to collect, mark, return to the water and recollect snails (the following day) in order to collect data that will allow students to make an estimation of the snail population.
Context for Use
Resource Type: Activities:Field Activity
Special Interest: Field-Based Teaching and Learning
Grade Level: Middle (6-8)
Description and Teaching Materials
This activity will take all or parts of three days. First, take the class out the lake or pond. Mark each group's boundary every 10 ft using the lath stakes. Once the group boundaries are marked, students can begin to wade out as far as you have determined is safe. Make sure to give this distance in feet to the students. Have the students collect a dozen or so snails. Return to the classroom and begin examining the snails. Have the students determine how many species there are. Have them draw and record the characteristics of the snail. Have them try to determine how the snail breathes, how they respond to an attack and what the little ridges on the shell indicate. These are inquiry based questions that will get them thinking and exploring. At the end of the class, collect the snails in a bucket and return them to the lake or pond.
On the second day, return to the area. Each group will need to stay in their area. They need to collect all of the snails they find in their area. They are to dry the shells off with a paper towel and mark them with a dot of nail polish. Make sure each group has a different color. The need to record how many snails they marked and released (S).
On the third day, they are to return to the area and count all of the snails in their area. This time they will count the total number of snails they find (T) and the number of marked snails they recover (N). After recording data and releasing the snails, return to the classroom. Use the formula: Population = T x S
You can also figure out the population density as well as the estimated total number of snails in the environment. It is really open ended from here.
Teaching Notes and Tips
A new wrinkle for me will be the species identification. This is modeled after what my MnSTEP class did with clams on the Mississippi River. Many students, as did many teachers with clams, won't know that there will be different species. If you have a more advanced class, this data will allow you to go further with your class and they can calculate a diversity index.