Fairy Shrimp, Group Of Small Primitive Crustaceans Found In Freshwater Ponds And Pools

Fairy Shrimp, group of small primitive crustaceans found in freshwater ponds and pools, especially during the spring and early summer. One type of fairy shrimp, the brine shrimp, lives in extremely salty waters in places like the Great Salt Lake, Utah, and evaporation basins used for commercial salt production. Some species of fairy shrimp have only been identified in a single pond while others occur throughout the world as far north as northern Alaska and Greenland. Only one species of a particular genus is usually present in one pond at a given time.

The fairy shrimp ranges from 6 to 50 mm (0.24 to 2.0 in) in length. It does not have a carapace, the hard outer shell that covers the head in many arthropods. Its compound eyes are on stalks that project sideways from the head. The fairy shrimp glides or swims upside down, moved by the propellerlike motions of its 11 pairs of delicate limbs.

Fairy shrimp eat debris and microscopic organisms such as algae, bacteria, protozoa, and rotifers. They collect food particles by straining the surrounding water with the delicate hairs on the edges of their feathery limbs. The food is concentrated along a groove that runs down the length of the underside of the body and is moved to the mouth with weak currents made by the moving limbs. A sticky secretion holds the food particles together until they are swallowed. Fairy shrimp are often nearly transparent, so they appear to take on the color of their food.

Females are generally more abundant than males. While mating, the male grasps the female with armlike clasping organs on his neck and may hold on for several days. The male dies within a few hours of transferring sperm and releasing the female. Eggs, which can develop with or without fertilization, are carried in a sac on the underside of the female’s body and are released in batches. The rate of egg hatching is affected by the salt content and the level of dissolved oxygen in the water. Two kinds of eggs are produced: thin-shelled “summer” eggs that hatch almost immediately, and thick-shelled “resting” eggs that can withstand both freezing temperatures and drying when their pools evaporate. Resting eggs are the only life stage of the fairy shrimp that can survive extremely harsh conditions, enabling the population to survive from one season to the next.

After hatching, the first larval stage is called a nauplius. It develops through 14 to 18 growth stages or instars, each ending with the shedding of its external skeleton. The number of segments and appendages along the length of the body increase as the fairy shrimp develops. The brine shrimp reaches maturity 18 to 21 days after hatching and lives for about four months.

Fairy shrimp may occur in very large numbers during their short breeding season and play an important role in food webs. One example is a species of brine shrimp found only in Mono Lake, California. Billions may live in the lake at one time providing a vital food source for migratory birds such as the California gull and the western eared grebe.

Scientific classification: Fairy shrimp make up the order Anostraca in the subclass Branchiopoda, subphylum Crustacea. The most common brine shrimp is classified as Artemia salina, and the Mono Lake brine shrimp is classified as Artemia monica.