When the Sun Rises: The Effect of Light on the Movement of Daphnia *

Abstract

Daphnia magna, commonly known as water fleas, are tiny freshwater crustaceans. They are filter feeders and can survive in culture (like an aquarium) by eating algae, bacteria, or yeast. A picture of a Daphnia is shown in Figure 1 below. You can purchase a culture kit from Carolina Biological Supply Company or you may be able to purchase them at a tropical fish store. (For more suggestions on specialty items you may need to culture Daphnia, check out the Materials section of a different Science Buddies science project that also uses Daphnia, Using Daphnia to Monitor Water Toxicity. Although they are small, Daphnia are big enough that you can easily watch them moving around in a fishbowl or small jar.

Photo of a water flea shows a translucent skin with organs visible and labeled. A heart is located near the top of the head and under a small layer of skin on its back. An egg sac is located below the heart on the middle part of its back. Three legs protrude from each side of the abdoment and two antennae covered in hairs hang from the front of the head.

Figure 1. Photomicrograph (a magnified image taken through a microscope) of Daphnia, the common water flea.

For this science project, you should first investigate how Daphnia normally migrate and swim around in different aquatic environments. Three different aquatic environments you can create and test include test tubes of water, large containers of water that simulate their pond habitat, and a real pond. How do the Daphnia swim during the day, when there is light, compared to when it is dark? In what direction do they swim? Do they show different patterns in where and how they move?

After you have investigated Daphnia's migration pattern in response to normal light, try testing different lighting sources to see how they change the movement patterns of the Daphnia. How do different artificial lights affect Daphnia's movement? Do different colored lights affect the movement, and, if so, do they affect it in a different way than the regular artificial lights? Can you explain their behavior? Even the tiny Daphnia can display complex behaviors in response to their environment!

Bibliography

• Clare, J. (2002). Daphnia: An aquarist's guide. Retrieved March 13, 2012, from Caudata.org: http://www.caudata.org/daphnia/

• National Institutes of Health. (n.d.). Daphnia. Retrieved March 13, 2012, from http://www.nih.gov/science/models/daphnia/

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Experimental Procedure

Variations

• How do other stimuli affect the movement of Daphnia? Think of other environmental factors, such as food availability, the presence of predators, or temperature, and devise a way to test how these other factors might affect Daphnia's movement.
• For other science project ideas that use Daphnia, see:
  • Using Daphnia to Monitor Water Toxicity
  • Caffeine and Heart Rate: A Pharmacological Study Using Daphnia magna

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