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Vernal pool fairy shrimp

 Photo of Vernal pool fairy shrimp

Scientific name: Branchinecta lynchi

Status: Threatened 

Critical Habitat: Designated 

Listing Activity: The vernal pool fairy shrimp was listed as threatened in September 1994. Critical habitat was designated in 2003. A recovery plan was published in 2005. A five-year review was conducted in 2007.

Potential Range Map

  • Description and Ecology

    Vernal pool fairy shrimp are translucent, slender crustaceans (relatives of lobsters, crabs, saltwater shrimp and barnacles). They are generally less than 2.5 centimeters (1 inch) in length, and swim on their backs by slowly moving their 11 pairs of swimming legs. They are unusual in that they use these same legs for breathing and feeding. They eat algae and plankton by scraping and straining them from surfaces within the vernal pool. They produce a gluey substance and mix it with their food before eating. Fairy shrimp are defenseless, and therefore occupy very temporary ponds, where aquatic vertebrate predators cannot survive.

    Branchinecta lynchi typically hatches when the first rains of the year fill vernal pools. They mature in about 41 days under typical winter conditions. Adult fairy shrimp live only for a single season, while there is water in the pools. Toward the end of their brief lifetime, females produce thick-shelled "resting eggs" also known as cysts. During the summer, these cysts become embedded in the dried bottom mud, and during the winter, they are frozen for varying periods. These cysts hatch when the rains come again. In fact, it appears that prior freezing and/or drying seems to be necessary for the eggs to hatch.


    At the time of its listing, the vernal pool fairy shrimp was known to occur only in California, extending from Tulare County in the south to Shasta County in the north. In 1998, these fairy shrimp were discovered in vernal pools in Jackson County, Oregon, in an area north of Medford known as the Agate Desert. Prior to this discovery, the most northerly known location for the species was south of Mount Shasta, California, some 80 miles south of the Agate Desert.


    Vernal pool fairy shrimp occur primarily in vernal pools, seasonal wetlands that fill with water during fall and winter rains and dry up in spring and summer. Typically the majority of pools in any vernal pool complex are not inhabited by the species at any one time. Different pools within or between complexes may provide habitat for the fairy shrimp in alternative years, as climatic conditions vary.

    Reasons for Decline

    Like the other species of vernal pool branchiopods, the number of B. lynchi populations have declined primarily because of destruction or degradation of vernal pools through development of urban, suburban, and agricultural projects. In addition to direct habitat loss, vernal pool fairy shrimp populations have declined from of a variety of activities that degrade existing vernal pools by altering pool hydrology (water regime). Vernal pool hydrology can be altered by a variety of activities, including the construction of roads, trails, ditches, or canals that can block the flow of water into, or drain water away from, the vernal pool complex.

    Conservation Measures

    A Wetland Conservation Plan is presently being developed for the Agate Desert area by federal, state, county, city, and private partners. The plan will designate areas in which development may occur, and areas which should be preserved to ensure the continued existence of this shrimp and the vernal pool ecosystem it occupies.

    References and Links

    U.S. Fish and Wildlie Service. 2005. Recovery Plan for Vernal Pool Ecosystems in California and Southern Oregon.

    U.S. Fish and Wildlife Service. 1994. Determination of Endangered Status for the Conservancy Fairy Shrimp, Longhorn Fairy Shrimp and the Vernal Pool Tadpole Shrimp; and Threatened Status for the Vernal Pool Fairy Shrimp. FR 59: 48136.

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