The Natural Habitat of Daphnias

Daphnias in Water Bodies

• Daphnias are found in open water and can also be found in water bodies that are formed seasonally. They are an important part of the food chain in the fresh water bodies. They are food for planktivorous fishes. The chances of finding a thicker population of daphnias are greater in a water body where such fish do not exist.

Ideal Living Conditions for Daphnias

• Daphnias live in waters with salinity up to 5 percent of sea water. But D magna species of daphnia can tolerate up to 20 percent of sea water. The life of a daphnia depends on temperature. During winter daphnias live longer, but usually not exceeding one year, their maximum life span. At a temperature of 3 degrees Celsius they may live up to three months and at 28 degrees Celsius their life span falls to less than a month. Daphnias survive well with a pH level range of 6.5 to 9.5, but the ideal is 7.2 to 8.5.

Size Does Matter

• Planktivorous fish prefer large sized daphnias. Daphnias of large size, D. magna and D. pulex, are targets of planktivorous fish and do not survive in the presence of such predators. Small sized daphnias such as D. cucullata, D. galeata, and D. hyaline are not found in fishless water bodies, which means that they are food for other species. These small daphnias become food for invertebrates.

Daphnias Living with Invertebrates and Fishes

• As invertebrates such as Chaoborus feed on small daphnias this causes considerable juvenile mortality. Daphnias living with invertebrates have developed an evolutionary strategy whereby they produce larger daphnia larvae. To avoid getting eaten by fish, daphnias have evolved to produce smaller babies.

Protection Against Predators

• Daphnias may take refuge behind submerged plants in shallow temperate lakes. In sub-tropical lakes daphnias avoid taking refuge among plants. They avoid free-floating plants more than the submerged plants.

  Several species of daphnia are now on the verge of extinction. If nothing else, they form a vital part of the fresh water food chain and sometimes are indicators of the ecological health of an area.