Vernal Pool Fairy Shrimp

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Vernal Pool Fairy Shrimp

Branchinecta lynchi

ListedSeptember 19, 1994
FamilyBranchinectidae (Freshwater shrimp)
DescriptionAn aquatic crustacean.
HabitatTemporary (vernal) pools.
ReproductionLays externally fertilized eggs.
ThreatsHabitat loss.
RangeCalifornia, Oregon


The vernal pool fairy shrimp ranges in body length from 0.4-1.0 in (11-25 mm). It can be differentiated from related species by the ridge-like basal segment outgrowth below and posterior to the pulvillus of the antennae of the male, and by the relatively shorter, pyriform brood pouch of the female.


The vernal pool fairy shrimp is typically active in adult form from about December to early May. The rest of the year it survives as persistent eggs. It matures and breeds quickly, allowing populations to persist in shallow, short-lived pools. If the pond is longer lasting, the vernal pool fairy shrimp can persist later into the spring or early summer.


The vernal pool fairy shrimp inhabits vernal (or temporary) pools with fresh, clear to tea-colored water. It usually occurs in mud-bottomed swales of grassy vegetation, or in basalt-flow depression pools in grasslands. One population, however, is known from sandstone rock outcrops, and another from alkaline vernal pools. The water in pools inhabited by this species typically has low concentrations of dissolved solids, alkalinity, and chloride, and has low conductivity. It often has a sporadic distribution within local complexes of vernal pools, in that not all pools in a complex are inhabited by the species.


Populations of the vernal pool fairy shrimp are known from California and Oregon, but are most numerous in central California. There are 32 known populations.


The habitat of the vernal pool fairy shrimp is imperiled by urban, commercial, and industrial development, the conversion of land from natural grassland into agricultural use, and activities to manage water supply and control flooding. Habitat loss is caused by destruction through changes in land-use, infilling, grading, and other activities, and by the modification of the watershed of the vernal pools. Overall, the most significant threats are associated with rapid urbanization and agricultural conversion. These human influences have already resulted in the loss of most of the original aquatic habitat of the vernal pool fairy shrimp. Moreover, 28 of the 32 known populations of the vernal pool fairy shrimp are considered by the U. S. Fish and Wildlife Service to be under threat.

Conservation and Recovery

The vernal pool fairy shrimp is not a protected species, and its critical habitat is not being effectively conserved. Some development projects affecting critical habitat have been required to institute conservation-related mitigations as a result of findings from environmental impact assessments. However, this has not always proven to be an effective way of avoiding or repairing damage to the critical habitat of the vernal pool fairy shrimp. Moreover, the artificial creation of vernal pools as compensatory mitigation has not been proven to be successful in dealing with the effects on dependent species, including the vernal pool fairy shrimp. Portions of four populations of the vernal pool fairy shrimp are on lands under public ownership, and the Nature Conservancy also owns and conserves some sites. Management plans for some federal, state, local government, and all Conservancy properties include provisions to protect vernal pools, but the plans do not specifically address the needs of the vernal pool fairy shrimp.


U. S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
Eastside Federal Complex
911 N. E. 11th Ave.
Portland, Oregon 97232-4181
(503) 231-6121

Sacramento Field Office, U. S. Fish and Wildlife
2800 Cottage Way, Room E-1823
Sacramento, California 95825-1846
(916) 978-4866


U. S. Fish and Wildlife Service. 1994. "Endangered and Threatened Wildlife and Plants; 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."