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Publication Extract
The following extract is Student Activity 7, pages 27 and 28, from the BES Publication, "Brine Shrimp Ecology"
Exploding Populations
 The Challenge
What happens if we put a male and a female brine shrimp in a container with food and adequate heating and lighting?
Would their numbers rise?
It would probably depend on how long we left them in the container but suppose we let the experiment run for a month, or a term - what will happen?
Does the amount of food the shrimps have during this period matter?
In this experiment you will set up a number of containers and monitor what happens in each one on a weekly basis.
How does the population of brine shrimps in a container change over time and what is the influlence of the feeding regime?
You might wish to put forward a hypothesis which you could test.
For example, one study found that females can produce about 100 eggs (which take about three days to hatch) in each brood and can produce a brood every 4-5 days, once they reach sexual maturity, at about 3-4 weeks old. So you might think that by the end of week 2 (i.e. two weeks after the sexually mature pair were put into the container) you would have about 200 newly hatched shrimps, plus the original male and female.
Apparatus that you will need
To set up this experiment you need the following items of equipment:
- nine plastic bottles (330 cm2 are fine)
- salt water (a concentration of 30-35 g per litre - this needs to be made up first)
- a plastic teat pipette, or dessert spoon, or sieve, to catch your shrimps from the holding tank
- nine gummed labels to identify each bottle
- substrate from the main brine shrimp tank
- bench lamps - to provide a source of heating and lighting for the shrimps during the month, or term, that the experiment is running
- liquid fertiliser and Liquizell.
Procedure
- Put 250 cm2 of salt water into each bottle and then add two dessert spoonfuls of substrate from the main tank and one drop of fertiliser. This will add algae and provide some food for the shrimps.
- Using the teat pipette, or the dessert spoon, or sieve, catch one female and one male from the main holding tank and put them into one of the bottles and label this bottle A. Then repeat with the other eight bottles, labelling them B, C, D, E, F,G,H and I.
- Put bottles A, B and C in a location where there will be adequate heating and lighting whilst the experiment is running and add to the label on each bottle 'control'. Bottles D, E and F can also be put in the same place, but add to the label on each bottle '1 drop per week'. Bottles G, H and I have the words '3 drops per week' written on each label and then the bottles can be put alongside the ofhers. Add the appropriate number of drops of Liquizell each week whilst the experiment runs.
- All being well, a few days later you will see the first eggs that the female has laid. These will be tiny brown grains, a little bit larger than pepper grains, and will probably be floating on the surface at the side of the bottle. When you first see the eggs or nauplii, add the stated number of drops of Liquizell only to the bottle as appropriate; record the date.
- At the time you set up the bottles, the population in each bottle will be two. [If one, or both, adults die before eggs are laid then replace the dead adult with another of the same sex]. Record the number of brine shrimps in each bottle and keep the records safe. At the start, the counting should not be too difficult but as the experiment goes on it may be best to empty the contents of the bottle into a larger container, like a beaker, whilst you count the shrimps in each bottle. Transfer them back into their 'home' bottle safely after counting them.
Results
Record your results in a table, keeping the data from the three different feeding conditions separate. Then draw a graph of the data in the best way you can; a line graph might be a good choice. You might find the average population size for each of the three conditions over time and on a separate piece of graph paper plot these data also.
How does the population in each bottle change over time?
How does the average population for each of the three feeding conditions change over time?
Has the Liquizell had an effect on the population sizes in the bottles?
Has your hypothesis been confirmed?
Copyright: BES Brine Shrimp Ecology Project: Homerton College Cambridge
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