 |
| 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
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