Fairy shrimp

Conservancy fairy shrimp (Branchinecta conservation)
• Endangered, Endangered Species Act

Longhorn fairy shrimp (Branchinecta longiantenna)
• Endangered, Endangered Species Act

Vernal pool fairy shrimp (Branchinecta lynchi)
• Threatened, Endangered Species Act

Conservancy fairy shrimp © 2009 Doug Wirtz

Habitat and Distribution

Fairy shrimp find their home in unique vernal pool ecosystems. Vernal pools are temporary wetlands, which fill with water during the fall and winter rains. The vernal pools provide important habitat for a variety of plants and animals that are well-adapted to extreme fluctuations of environmental conditions. Although multiple species of fairy shrimp thrive in the same type of vernal pool habitat, generally members of more than one species do not co-occur within the same vernal pool, indicating that species are strongly competitive against each other. The three species of fairy shrimp that can be found within the Los Padres National Forest and Carrizo Plain National Monument are the Conservancy fairy shrimp, longhorn fairy shrimp, and vernal pool fairy shrimp.

The Conservancy fairy shrimp is named in honor of the Nature Conservancy, which has worked to protect vernal pools in California for decades. This species can only be found in two areas on Earth:the California Central Valley and southern California. Within the Los Padres National Forest in Ventura County, there are two locations where the Conservancy fairy shrimp has been documented, although they may occur in other areas within the forest as well. The vernal pools within the Los Padres that support Conservancy fairy shrimp are unique as they are located under a pine forest canopy rather than annual grasslands where most Conservancy fairy shrimp tend to be found. Conservancy fairy shrimp usually occur in pools that are relatively large and turbid at elevations from 16 to 5,577 feet and at water temperatures as high as 73°F.

Longhorn fairy shrimp are more particular about the habitat they require when compared to the Conservancy fairy shrimp. They have been found in grassland vernal pools with temperatures between 50 – 64°F. Longhorn fairy shrimp are extremely rare and populations are widely spread throughout northern and central California. There have been documented populations in the southern end of the Carrizo Plain National Monument in the Carrizo Vernal Pool Region.

Vernal pool fairy shrimp, are slightly more common than the previous two species, and can be found as far North as Jackson County Oregon. Vernal pool fairy shrimp are also known to occur as far south as the Los Padres National Forest in Ventura County, where they are found in the pine canopy vernal pools.

Identification, Biology, and Life Cycle

Fairy shrimp are branchipods, a type of crustacean characterized as small fresh water animals that feed on plankton and detritus (organic matter). Fairy shrimp range in size from ½ to 1 inch, are typically off-white to grey in color, and lack an outer hard shell. Fairy shrimp feed on bacteria, algae, protozoa, and bits of organic matter. They provide an important food source for tadpole shrimp, backswimmers (aquatic insect), aquatic beetles, aquatic insect larvae, salamanders, killdeer (shorebird), and ducks.

Fairy shrimp move through the water by slowly beating their eleven pairs of short swimming legs (called phyllopods) in a wavelike movement while they lay on their back. Their phyllopods also act as gills allowing the fairy shrimp to absorb dissolved oxygen as they move.

It is difficult to distinguish one fairy shrimp species from another, and many of the differences can only be seen with a microscope and generally requires formal training. For example, the conservancy fairy shrimp is distinguished from other fairy shrimp by the shape of the two humps on the distal segment of the male’s antennae, as the larger hump is towards the tail rather than the head. In females the location of the brood pouch, where eggs are protected before hatching, distinguishes the fairy shrimp. In a typical vernal pool female shrimp commonly outnumber male shrimp.

The invertebrate’s life cycle is short lived, and well-adapted to seasonal variation that the vernal pools in which it occurs experience. It is the life cycle of the fairy shrimp that allows the species to survive and pass on genes each generation. After rapid breeding occurs between the male and female fairy shrimp, the female’s fertilized eggs will fall to the bottom of vernal pools or the eggs will remain in her brood sac after she dies. Once at the bottom of the pools, the fertilized sacs — called cysts — remain dormant until the pools dry out in the spring and summer months. The living generations of fairy shrimp die when the pools dry out. However, the cysts that contain the new brood can withstand desiccation through the hot and dry summers. The next generation’s life cycle begins again when the vernal pools are once again immersed in fresh water. The cysts can also be transported through predator consumption, which helps to distribute the fairy shrimp populations.

Threats and Conservation

Vernal pools are considered one of the most threatened habitats in the world, and many of the historic vernal pools in California have been lost to development, highway expansion, agriculture, and wetland draining. As vernal pool habitats are dependent on the watershed dynamics in a given area, the modification of watersheds upstream of vernal pools also threatens vernal pool ecosystems. This habitat destruction or alteration is the largest cause of the decline in fairy shrimp populations.

Species conservation for fairy shrimp involves protecting the species’ habitat. Designated vernal pool regions may have species recovery plans that are based on the presence of the species and the number of vulnerable vernal species within each pool. The sites chosen to protect the species are generally protected from development; however, changes in hydrology miles upstream from vernal pool habitats can affect the surface hydrology, and lead to disappearance of the downstream vernal pool ecosystems. Because the various species of fairy shrimp share the same ecosystem needs, they also share similar threats. It is therefore necessary that conservation measures be focused on protecting the unique vernal pools required by fairy shrimp to survive.