This is a small and primitive relative of crabs and lobsters, found in very salty water in many parts of the world, from Greenland to Australia and from the West Indies to Central Asia. In southern Europe, and formerly in England, it has been found in the shallow ponds where sea water has evaporated to produce a high concentrated salt solution. There, though each hrimp is less than ½ in. long, it may be so abundant as to colour the water red. (The red colour is due to the red, oxygen-carrying pigment haemoglobin.)

The brine shrimp has two pairs of antennae, two compound eyes on stalks, and a third, small, eye in the middle of its head. It has 11 pairs of limbs. With the latter, it swims upside down—or rather with its ventral surface to the light, for it will turn over if illuminated from below (see page 120).

The physical appearance of the animal varies a little with the amount of salt in the water in which it grew up. As a result, some spurious species have been described. One of these, Artemia milhauseni, was exposed in 1875 when identical animals were produced from Artemia salina reared in a certain concentration of saltwater.

The brine shrimp feeds on the tiny particles of aorganic matter suspended in the water through which it swims. The rippling motion of the 11 pairs of flattened limbs, each one-sixth of a beat ahead of the pair in front, sweeps the particles in currents of water backwards along the front of the body. The particles are caught in strainers formed by the bristles on the inner edges of the limbs and are thence transferred forward to the mouth.

During reproduction the male brine shrimps clasp the females by means of specially modified antennae. The females have a brood pouch attatched to the body behind the limbs, where the larvae remain for some time before being liberated when conditions are favourable to their survival. The young are active, with short bodies, no limbs, but large antennae, used for swimming. These so-called "nauplius" larvae become adults after a succession of moults and, in a warm room, become mature in 3 weeks. Some colonies have females only and in these the eggs develop without being fertilized (parthenogenesis). Sometimes, and as a result of mating and parthenogenesis, eggs are laid that may either hatch very soon or lie quiescent for long periods. Such "resting" eggs have hard brown shells and can be dried and kept for years before being hatched in salt water. Since many of the ponds and lakes in which brine shrimp live owe their extreme saltiness to the evaporation of water, and may dry up completely, the value of an egg that can survive the complete disappearance of water is obvious.

This is also very convenient for aquarists, who use brine shrimp as fish food. They buy the dry eggs and hatch out the larvae, rearing them to adulthood in seawater on a diet of yeast. The eggs they buy are packaged in various parts of North America.

It is remarkable enough that the resting eggs should be able to survive for years when dried out, but this is not the limit of their tolerance. By drying them in a high vacuum, practically every trace of water can be removed and then the chemical processes of life are brought to a complete standstill. If such dried eggs are cooled to the temperature of liquid air, around –190 C/ -310 F, they will still hatch when returned to salt water at a normal temperature. Moreover, provided they are fully dry, a small proportions will even survive for 2 hours a temperature of 105 C/ 221 F. To be boiled an live is quite an achievement!

The adults, too, are unusual in their tolerance of harsh conditions, but in a different way. They can be found in water so full of salt that crystals form around the edge of the pool. Such water would contain about 30% of salt as compared with the 3 ½% present at sea. In the laboratory, on the other hand, they will survive in sea water diluted to only a tenth of its normal strength. Curiously, however, although they can live in the se, they do not do so and in nature live only in water that is more than twice as salty, e.g. in salt pans or salt springs. The explanation seems to be that they would be bery vulnerable to many kinds of predators in the sea and that they can flourish only in water too concentrated for these potential enemies to survive. Thus are they literally preserved in brine!

A problem facing all animals living in water containing concentrations of salts different from those in their body fluids is that of preserving a proper internal balance of water and salts. This is because the concentrations of each constituent in the body tend always to equalize with those outside. An animal living in freshwater has to prevent the salts from leaking out of its body and one living in concentrated salt solutions has to prevent too many salts flooding into its body. The brine shrimp has to keep its internal salt concentration lower than that of the surrounding brine, as low indeed as that of a freshwater animal, by absorbing salty water from its alimentary canal and expelling the surplus salt through special gill areas on its limbs. In devoting its energies to this, it need expend far less on escaping predators—few of whom can survive in the brine shrimps rigorous environment.

Phylum_____Arthropoda__

Class_______Crustacea____

Sub-class____Branchiopoda

Order_______Anostraca___

Genus

& species____Artemia salina
 
 

Materials (per group) 100 ml brine shrimp mixture 2 each, 100 cm tygon tubing 10 ml graduated pipette 4 corks 8 small beakers or cups

meter stick clear spot plate 8 tube clamps stereomicroscope wax pencil  flood lamp

Procedures
1. Carefully hold a piece of tygon tubing in a "horseshoe" shape. Using a 10 ml pipette, fill the tygon tubing with 50 ml of shrimp mixture. Stopper one end and then the other end. If the tubing is longer than 100 cm, hold the tube vertically and apply a hose clamp at the point on the tube where the meniscus is. Place three loosened hose clamps approximately 25 cm apart so that the tube is divided into four equal sections each containing 12.5 ml of mixture.
2. Repeat step 1 with a second piece of tubing.
3. Tape the tube to a lab table top so that it is straight and cover with a piece of cloth so that it is in the dark.

Control (dark tube)
4.. Wait overnight and tighten the middle clamp first, then the end clamps. This divides the tubing into four sections.
5. Pour the contents of each section into a small beaker.
6. Draw a 1-mL sample from each beaker and put in a second beaker along with 9 ml of water. This dilutes the sample by a factor of 10 so you aren't counting shrimp forever.
7. Draw 1-ml of diluted mixture and place in a spot plate.
8. Count the number of shrimp present. Multiply this number by 10 and again by 12.5 to estimate the total number of shrimp in the section.
9. If time permits, repeat steps 6, 7 and 8 up to five times and compute the average number of shrimp for each section.
10. Record your group's result  (average per section) in the table below.

Experimental (Light tube)
11. Tape the second piece of tubing on a table so that it is straight. Place a lamp so that the bulb is directly over the middle of the first section. Leave overnight.
12. Repeat steps 5-10 for the experimental tube the next day.

Hypothesis:  Prior to counting the shrimp make a hypothesis as to which section of the lighted tube will contain the most shrimp:
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Questions and Conclusions

1. Based on your results, which light intensity is preferred by the brine shrimp? Explain.
 

2.Contrast your data to the class average - is there a difference? Why or why not?
 

3. Which light intensity is least favorable? Explain.
 

4. Why was the dark condition control needed?
 

5. Do your data support your hypothesis? Explain.
 

Conclusion: How do brine shrimp respond to light intensity?
 

Extension: If your were going to use this experimental design for your inquiry project how would you modify it? What questions would you ask?