Water fleas, primarily belonging to the genus Daphnia, are small, common crustaceans found in various freshwater environments. These tiny aquatic organisms are filter feeders, using specialized legs to strain microscopic particles from the water. Their rapid reproduction rates contribute to their abundance in aquatic ecosystems. Water fleas play a significant role at the base of many aquatic food webs, serving as a food source for numerous other organisms.
Tiny Hunters of the Pond
Many smaller organisms actively prey on water fleas. Aquatic insect larvae are prominent predators, including larvae of damselflies and dytiscid (aquatic) beetles. Phantom midge larvae also consume water fleas, utilizing specialized hooks and floats to capture them.
Hydra, small freshwater invertebrates related to jellyfish, consider water fleas a common food source. These creatures capture prey using tentacles armed with stinging cells called nematocysts, which inject venom to paralyze or kill the water flea before ingestion. Some predatory zooplankton, such as certain copepod species and even other types of water fleas like spiny water fleas, also consume smaller water fleas. Spiny water fleas, an invasive species, specifically eat other zooplankton, including Daphnia.
Fish and Amphibian Appetites
Fish are significant consumers of water fleas, especially during their younger developmental stages. Many species, including guppies, minnows, and the young of larger fish like bass and trout, rely on water fleas as a primary food source. Other fish such as yellow perch, walleye, white bass, alewife, bloater chub, chinook salmon, emerald shiner, spot-tail shiner, rainbow smelt, lake herring, lake whitefish, and deepwater sculpin also feed on water fleas. Small rasboras, danios, pea puffers, livebearers, and certain small cichlids readily consume water fleas.
The jerky swimming movements of water fleas activate the hunting instincts of fish, making them an appealing live food. Tadpoles of various amphibian species also feed on water fleas. Small adult amphibians may also consume water fleas as part of their diet. Water fleas provide important fiber for fish due to their chitin content, which aids in healthy intestinal function.
Birds and Beyond
Some birds, particularly dabbling ducks and other waterfowl, can inadvertently consume large quantities of water fleas while filter feeding in aquatic environments. These birds typically feed on a variety of small organisms and plant matter present in the water. While not their primary prey, water fleas can be an incidental part of their diet.
Larger aquatic insects, such as water boatmen and backswimmers, may also include water fleas in their broader diets. Backswimmers are carnivorous and can prey on small crustaceans like Daphnia, along with other small aquatic organisms. Water boatmen, while primarily feeding on plant debris and algae, might also consume water fleas.