Brine Shrimp Experiment: Testing the Effect of pH

Figure 1 - Artemia monica from Mono Lake

Brine shrimp, Artemia ( figure 1), belong to the class Crustacea, along with prawns, lobsters, crayfish and yabbies. Also known as 'sea monkeys', they thrive in inland lakes and salt pans that have salt concentrations of up to 25%. A slightly alkaline pH is also required for their survival. In the USA the Great Salt Lake (figure 2), Mono Lake and San Francisco Bay are good sources of Artemia. In Australia, a related species, Parartemis, thrives in saline lakes.

In these salty conditions, brine shrimp have few predators, coupled with an abundant supply of algae to feed on. Brine shrimp eggs (cysts) can remain dormant for years if left dry. When conditions of temperature, salinity and pH become suitable, these cysts hatch to form larvae, or "nauplii." The total life cycle span for Artemia is around one year.

Male brine shrimp are identified by the large pair of "graspers" on their heads. Live brine shrimp or their eggs are harvested for use as tropical fish food in the aquarium and aquaculture industries.

The Effect of pH on Brine Shrimp – Materials and Teaching Method

Figure 2 - Great Salt Lake, Utah

A simple definition for pH is that it describes the acidity, or hydrogen ion concentration, of a solution. Specifically, a solution’s pH is equal to minus the log base 10 of its hydrogen ion concentration , so a high pH indicates low acidity, or alkaline conditions, and a low pH indicates high acidity. Universal indicator paper can be used in this activity to estimate the pH of the various solutions tested.

The following materials and equipment are required per group of around four students:

•                non-iodised table salt

•                sodium carbonate

•                vinegar

•                three large test tubes

•                magnifying glass or stereo microscope

•                three 250ml beakers

•                teaspoon

•                universal indicator paper and colour chart

Students should be instructed to copy down the following directions after a teacher-led explanation.

•                Pour 200ml water into each of three beakers. Label these beakers "1," "2" and "3."

•                Add 1 teaspoon salt to each beaker.

•                Add 1/4 tsp sodium carbonate to beaker 2.

•                Add 1/4 teaspoon vinegar to beaker 3.

•                Pour equal amounts of liquid from these beakers into three large test tubes, also labelled "1," "2" and "3."

•                Drop a piece of indicator paper into each test tube and record the pH of each. Determine whether the liquid in each tube is acidic, basic or neutral.

•                Cover the surface of the liquid in each of the tubes sparingly with brine shrimp eggs. Leave the test tubes in a warm place for 24 hours.

•                Observe, count and draw any brine shrimps as they hatch over the next few days.

Students should record their results in a table. Columns could be labelled "pH of test tube," while the rows could be headed "Number of brine shrimp hatched: Day 1, Day 2, Day 3 etc." Hatching rates should be more successful in the alkaline test tube (i.e. tube 2).

Brine shrimp could be observed under a magnifying glass or stereo microscope and then drawn and labelled (see figure 1). Students may also observe their locomotion and investigate how they respond to a light source such as a torch.

The following questions can be written on the board after students write up the experiment and their observations:

1.             Draw a diagram of one or more of your brine shrimps. Try to identify them as male or female.

2.             What do you think is the optimum pH for the growth of brine shrimp?

3.             Describe the swimming motion of brine shrimp.

4.             Use resource material to find out whether brine shrimp reproduce sexually, asexually or if they reproduce using both methods.

5.             How do brine shrimp respond to a light source such as a torch or microscope lamp?

Brine Shrimp Follow-Up Activities

Further experiments could be designed to test the effects of pollution, temperature and salt concentration on Artemia hatching rates. As in all controlled experiments, all variables except for the one being tested must be kept constant. In other words, if temperature is being tested, the other variables such as volumes, pH and salt concentrations must be kept the same for each test tube.

If students wish to keep the brine shrimp for an extended period they can feed them with small amounts of dried yeast or Spirulina algae (available from pet shops). They should ensure that the water is changed regularly and replaced with appropriate amounts of salt and sodium carbonate.

References

Brine Shrimp Direct, 2010,'Brine shrimp in the Classroom', brineshrimpdirect.com

Science Netlinks, 2001, 'Brine shrimp 2: Brine Shrimp Survival', sciencenetlinks.com