What are they?
Cladocera also known as Water Fleas are a small aquatic crustacean that are part of Branchipoda class. They originated in the Palaeozoic era between 250 and 500 million years ago. Currently, there are 620 known species. They are found worldwide and can live in brackish and freshwater habitats, with only a few species being found in marine environments. They may be called fleas because their swimming strokes of the appendages make the animals move in tiny jumps. They are typically split into two separate groups: pelagic free-swimming forms and benthic crawling forms
They are important as bacterivorous, herbivorous or detritivores grazing on phytoplankton, algae, bacteria, or dead plant material. Cladocera are also important prey species of larger zooplankton and small fish. Cladocera also engage in one of the largest daily migrations – daily vertical migration. They spend the day at depth to avoid predators and migrate to the surface at night to feed. Even though this involves experiencing a vast change in hydrostatic pressure, they are capable in handling this.
They are holoplanktonic. Live around 50 days, become sexually mature at around day 14/15. Range from <250µm to ~5mm. They either produce 2 or up to 300 eggs at a time. They mainly produce with cyclic parthenogenesis. During favourable environmental conditions, parthenogenic reproduction takes place. During this time, females asexually produce many female offspring that in turn asexually produce more female offspring. This cycle can last for several generations and sometimes entire Cladocera populations are made up of only female individuals. When environmental conditions become poor, females start asexually producing both male and female offspring, which leads to a short cycle of sexual reproduction. Fewer offspring are produced this way, but they are long lived dormant eggs, that hatch once environmental conditions become favourable
By Tara Sweetman