- Brine shrimp are small arthropods which live in tidal pools, estuaries, and salt lakes. The salt concentration of these environments can vary greatly. In this experiment, you will hatch brine shrimp eggs in different salt concentration solutions to find the optimal salt concentration for brine shrimp eggs to hatch. This lab will take 5 days to complete (not including the solution preparation).
- The unit of concentration you will be using is parts per thousand (ppt). In a solution, this is the number of volume units of solute (sea salt) per 1000 volume units of solution.
MATERIALS:1000 mL of bottled or dechlorinated water
5 plastic-foam cups
5 plastic lids to fit cups (or aluminum foil)
Wax marking pencil
100 mL graduated cylinder
Balance
40 g synthetic sea salts
4 containers with lids to store salt solutions.
0.5 g brine shrimp eggs
Eyedropper (marked for 0.5 mL), or 5 separate droppers
5 petri dishes
Hand lens or stereomicroscope
Five different colored pencils
Graph paper- You can get sea salt and brine shrimp eggs at any pet store. Sea salt costs about one cent per gram, and the eggs are about five dollars for 6 grams.
PREPARATION OF SALT SOLUTIONS:
You may use dechlorinated tap water instead of bottled drinking water, but the bottled water should be salt free. To dechlorinate tap water, let it stand for 24 hours.
P.1 Prepare the 80 ppt solution by dissolving 40 g of sea salt in 500 mL of water. Put in labelled container and let it sit overnight.
P.2 Use the following table to prepare 60 ppt, 40 ppt, and 20 ppt solutions:
80 ppt
SolutionBottled
WaterResulting
Solution150 mL 50 mL 60 ppt 100 mL 100 mL 40 ppt 50 mL 150 mL 20 ppt Put solutions in labelled closed containers.
PROCEDURE:
1. Label five plastic-foam cups as follows: 0 ppt, 20 ppt, 40 ppt, 60 ppt, and 80 ppt.
2. Pour 200 mL of fresh bottled water into the cup marked 0 ppt.
3. Pour 200 mL of each solution into the appropriately marked cups.
4. Measure 0.1 g of brine shrimp eggs for each of the five cups. Pour the eggs into the labelled cups. Cover each cup with the plastic lids or aluminum foil., and place the cups where they won’t be disturbed. This day would be called day 0
5. Each day for 2-4 successive days, use a dropper to remove 0.5 mL of solution from each cup. If you use a different dropper for each of the 5 test solutions, the procedure will go quicker. If only one dropper is used, clean and dry it between each solution. Stir the solution in each cup before taking the sample. This will mix the eggs and hatched brine shrimp evenly throughout the solution. Place each solution sample into a clean petri dish, and examine it with a hand lens or stereomicroscope. Count the number of eggs and hatched brine shrimp, and record the numbers in the DATA TABLE.
Do NOT return eggs or shrimp to the cups.
DATA TABLE:
Number of Hatched Brine Shrimp and Eggs Per 0.5 mL Sample.
Day 1 Day 2 Day 3 Day 4 Cup Salinity Number
of eggsNumber
of shrimpNumber
of eggsNumber
of shrimpNumber
of eggsNumber
of shrimpNumber
of eggsNumber
of shrimp
1
0 ppt
2
20 ppt
3
40 ppt
4
60 ppt
5
80 pptRESULTS:
6. From your data collected, what is the optimal salt concentration for hatching brine shrimp?
- Optimal salt concentration = ______ ppt.
GRAPHING:
- Graphing is an important tool of the scientist. It allows you to compile your raw data into an easy to interpret form. We always graph a variable against a constant. This allows you to to see the effect of the constant on the variable. The variable is usually placed on the vertical axis, and the constant on the horizontal axis.
- You will be graphing time in days on the horizontal, or x axis. Number your horizontal axis from 0 to 5. The vertical, or y axis will be the number of shrimp per 0.5 mL sample. Look at your raw data (for all 5 concentrations) to determine the numbers you will use. Again you will start at 0. Try to use as much of the graph paper as possible. This makes your graph more accurate and easy to read.
- You will be graphing five lines on your graph. A separate line for each salt solution concentration. Choose five different colored pencils (one to represent each concentration). Now choose one of the sets of data for a concentration, and plot your points on the graph.
- When we plot a graph, we do not connect the points, but instead we draw the best line of fit. Our data points from the raw data almost never fall on the line that they belong. This is because of experimental error. When we fit a line to our points, we draw the line the points should have been on. This is somewhat like an average, in that the line we draw is the best representation of our data points. The line may or may not go through any of our points, but it will have about equal points above and below it, which are about the same distance from the line. The correct answers are then any point along the line, and not the raw data points. Now fit your line to your points. The line will start at x=0, y=0 and be a smooth curved line. Repeat this procedure for your four other concentrations, using a different color pencil for each.
- Now make sure your graph has all the necessary information. Your graph needs a title to identify what it represents. In addition to the numbers, your horizontal axis and vertical axis need labelled to identify them and give value to the numbers. Because you have five lines representing the five different concentrations, you need a key which identifies which line represents which concentration.
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- The unit of concentration you will be using is parts per thousand (ppt). In a solution, this is the number of volume units of solute (sea salt) per 1000 volume units of solution.
FINDING THE OPTIMAL SALT CONCENTRATION
FOR HATCHING BRINE SHRIMP
INTRODUCTION: