Vesikirppuja

Vesikirppuja, commonly known as water fleas, are small planktonic crustaceans belonging to the order Cladocera. They are found in freshwater habitats worldwide, from ponds and lakes to slow-moving streams. Despite their name, they are not fleas but are more closely related to crustaceans like shrimp and crabs. Their size typically ranges from 0.2 to 5 millimeters, making them microscopic to the naked eye for most species.

Water fleas are characterized by a bivalve carapace that encloses their body, except for the antennae and legs. They use their large, prominent antennae for swimming, propelling themselves with a jerky, hopping motion, which is the origin of their common name. Their diet consists mainly of algae, bacteria, and other small organic particles suspended in the water, which they filter using specialized mouthparts.

A remarkable feature of water fleas is their reproductive cycle. They can reproduce asexually through parthenogenesis, where females produce offspring without mating. This allows for rapid population growth, especially in favorable conditions. However, when environmental conditions become unfavorable, such as a decrease in food availability or temperature, they can switch to sexual reproduction, producing resting eggs called ephippia. These ephippia are highly resistant to harsh conditions and can remain dormant for extended periods, hatching when conditions improve.

Water fleas play a crucial role in aquatic ecosystems as primary consumers, feeding on algae and other microorganisms. They are also an important food source for larger aquatic animals, including fish and invertebrates, thus forming a vital link in the food chain. Their populations can serve as bioindicators, reflecting the health of their aquatic environment due to their sensitivity to pollution and changes in water quality.