Environmental Differences Author: Jolene Routson

Overview: Students will observe and conduct an experiment to see whether differences in salinity (the environment) have an affect on the hatching rate and survival of brine shrimp.

Lesson Concepts:

• Environmental changes may affect an organism’s ability to survive.
• Scientists work to create and address questions.

Grade Span: 3–5

Materials:

• Vial of brine shrimp eggs (available at most pet stores or online)
• Aquarium salt
• Five jars or plastic cups per group
• Measuring cup/tablespoon
• Science journal for each student
• Brewer’s yeast

Advance Preparation:

— Purchase vials of brine shrimp and aquarium salt from a pet supply store.
— Prepare five solutions in enough quantity for each group to have about a cup of each. Determine the amount of salt used on quantities indicated in the instructions on the salt package. The solutions are: plain water; 1/2 prescribed salt; salt prescribed in directions; 1-1/2 prescribed salt; double prescribed salt. To dissolve the more highly concentrated salt solutions you may need to initially use warm water.

Time: One class period for initial set up. Approximately 10–15 minutes for daily observations.

Grouping: Pairs or threes

Teacher Background:

Brine shrimp (Artemia franciscana) are found widely in North America. They can be found south of San Francisco in places where salt water evaporates naturally along the California coast, and in the Great Salt Lake, Utah. Brine shrimp can also be found in salt flats and are an important food source to many wildlife species such as flamingos.

Brine shrimp are only distantly related to the shrimp we eat. Among the closest relatives to the brine shrimp are the fairy shrimp, which are common in fresh water ponds. Although brine shrimp grow very well under artificial conditions, they are not found in the open ocean. This is because the brine shrimp’s only defense mechanism against predators is its habit of living in hyper-saline bodies of water. Brine shrimp have evolved the most efficient osmoregulatory system in the animal kingdom.

Brine shrimp are non-selective filter feeders. They will feed on anything that is the right particle size (between 5–50 microns). Feeding is not necessary if tiny microscopic plants or algae start to grow in the containers. If containers are placed in natural light, bacteria and algae growth will be stimulated. However, powdered brewer’s yeast is also an option and is readily available in grocery stores. A general rule for feeding is to administer no more than will disappear and leave the water crystal clear in two days. Feeding once or twice a week should be sufficient (Note: it is not necessary to feed shrimp until they are hatched).

Teacher Resources: Photographs of brine shrimp and interesting information can be found at www.monolake.org/naturalhistory/shrimp.htm.

Explore these links for additional information on the topics covered in this lesson:

• Nature of Science
• Adaptation

Teaching Tips:

Brine shrimp tend to be fairly resilient to varying conditions, however it is important to keep shrimp in a fairly warm location. (Note: Room temperature is acceptable, however, warmer temperature may promote faster growth.)

• It is not recommended to use pickle jars for raising brine shrimp. Even after thorough washing, shrimp tend not to hatch and grow in this environment.
• Discuss evaporation, as it will be necessary to refill jars regularly. Remember, water evaporates and salt does not. Compensate for evaporation by refilling with distilled water or tap water.

Vocabulary: Environment, salinity, evaporation, and observation

Procedure:

1. Discuss the difference between fresh and salt water with the students. Make sure they know where each occurs.
2. Set up five containers of water per group. One of each concentration of salt.
3. Sprinkle a pinch of eggs onto top of salt water in each container. Observe and record changes to each jar.
4. Have students create a chart for each of the five jars showing the proportion (or actual number) hatched and subsequent development. Illustrations may be useful for later discussions pertaining to form and function.
5. Hold a class discussion of the results. Questions to pose: Is there a difference in results between the five salt solutions? How much difference? Based on the results of this experiment, what other questions would students like to ask?
6. Noting that brine shrimp have no discernable defenses or escape mechanisms, and assuming that the class results show that brine shrimp can survive in very salty water (too salty for fish to live), ask students to discuss what advantage brine shrimp might gain in the wild from being able to live in such an environment.

Extensions:

Ideas for additional experiments:

• Can brine shrimp be fed too much?
• Who can keep brine shrimp alive the longest?
• Do brine shrimp prefer light or dark?