Snails: Population Calculation in an Aquatic Environment
Summary
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.
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Learning Goals
Students will learn characteristics of aquatic snails and determine the snail population in a given ecosystem.
Context for Use
This field study works great for 7th graders. It gets them outside in the spring of the year. You do need the weather to cooperate; overly cool or windy weather makes it quite difficult. You also have to have a class that can handle wading into the water. Finally, you need a place to go. We have a lake right out our backdoor that we use.
Description and Teaching Materials
Divide the class into groups of three. Each group will need two pieces of wood lath for stakes, a notebook, some paper towels and some nail polish.
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
N
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.
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
N
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
Stress safety and limit how far out students can go. Make sure students adequately dry the snail shells before applying the nail polish or it won't stick and it will skew the data.
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.
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.
Assessment
Make sure they turn in their data as well as all of their calculation. Also have them turn in their answers to the inquiry questions and finally have them write a conclusion to the lab.
Standards
.1.1.1.1, 7.1.1.1.2, 7.1.1.2.1