Daphnia (Water Flea)

Daphnia (Water Flea)

Fun facts..

What are they?

Daphnia, commonly called water fleas, are a freshwater zooplankton found in ponds and lakes all over the world. Daphnia received the name water flea due to their jerky swimming motions. Some types of Daphnia can be seen with the human eye, while others must be identified with a microscope. Depending on the species they can range in size from 0.5mm to 1cm. Their outer covering, or carapace, is transparent, so many internal organs can be seen, especially the beating heart. On the head there is a compound eye and a pair of antennae, which are used for swimming.

Their role in the foodchain..

Daphnia are an extremely important part of aquatic food chains. They eat primary producers such as algae, yeast, and bacteria. Daphnia are the prey of tadpoles, salamanders, newts, aquatic insects, and many types of small fish. Fluctuations in Daphnia populations can cause algae overgrowth or even a drastic drop in fish populations. Through the food chain, larger animals caught or eaten by humans can be affected by large changes in Daphnia populations

Reproduction..

The Daphnia lifespan is approximately eight weeks. Daphnia reach maturity quickly, within five to ten days, and produce multiple offspring each cycle. Daphnia can reproduce both asexually and sexually. During times of plentiful food, females reproduce asexually to produce clones. When food is scarce, Daphnia reproduce sexually in order to produce genetic variation and increase the chance of species survival. During harsh weather conditions, resting eggs are produced. These eggs have a tough outer coating, which can withstand time, heat, drying, and cold temperatures.

To summarise..

• Daphnia are often called water fleas because they swim in a jerky motion.
• Daphnia are extremely small and range in size from 0.5mm to 10mm.
• Daphnia can be found in freshwater lakes, ponds, and rivers all over the world.
• The outer carapace of a Daphnia is transparent so all the internal organs, even the beating heart, can be seen.
• Daphnia mature in approximately a week and can have thousands of offspring. Daphnia are very important to the food chain.
• They eat algae and are eaten by insects, water mites, and small fish.
• In the presence of a predator Daphnia can develop large head and tail spines.
• Daphnia are very sensitive to changes in their environment.
• In low oxygen water conditions Daphnia can increase hemoglobin production, which causes them to turn red.
• During unfavorable weather conditions Daphnia can produce resting eggs, which can withstand time, heat, cold, and drought.

Their lifestyle..

..Special adaptations..

When the environment becomes stressful, Daphnia adapt by producing male as well as female embryos. Once they become mature, these individuals breed and produce fertilized eggs that are encased in tough protective shells. These are released from the female's body and will have to go through several cycles of freezing and thawing before they hatch.

It is difficult to distinguish male and female Daphnia. They are basically identical except that males are generally smaller in size, have larger antenules, and the first legs have a stout hook used in clasping the female during mating.

How do they respire?

Daphnia swims with a jerky motion through the water as the powerful 2nd antannae are thrust downward. The stroking action moves the animal towards the surface. Then it pauses for a short while before the next stroke, falling toward the bottom of the pond. This is when it breathes and captures food. Five pairs of legs inside the body covering (it is open in the front) are used to capture tiny microscopic food. They are finely-branched, and they also aide in breathing as the animal collects oxygen from the water.

Special Adaptations..

In a good environment, most Daphnia are female and will reproduce without breeding, through a natural form of cloning. When reproducing this way, the eggs do not get fertilized, so the young are exact copies of their mothers. The unfertilized eggs develop into live embryos inside the female's body, and the young are released into the environment within two to three days.