''Branchinecta sandiegonensis'' is a rare species of

crustacean Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, amphipods and mantis shrimp. The crustacean group ...

in the family

Branchinectidae Branchinectidae is a family (biology), family in the order Anostraca (fairy shrimp), containing two genera – ''Branchinecta'' and ''Archaebranchinecta''. The majority of the species are in the genus ''Branchinecta'', with only ''Archaebranchine ...

and the order

Anostraca Anostraca is one of the four orders of crustaceans in the class Branchiopoda; its members are referred to as fairy shrimp. They live in vernal pools and hypersaline lakes across the world, and they have even been found in deserts, ice-covered m ...

, the fairy shrimp. Commonly known as the San Diego fairy shrimp, it is named after the vernal pools found in

San Diego County, California San Diego County (), officially the County of San Diego, is a county in the southwestern corner of the U.S. state of California. As of the 2020 census, the population was 3,298,634, making it California's second-most populous county and the fi ...

, where this species was originally discovered.Fugate, M. (1993)
''Branchinecta sandiegonensis'', a new species of fairy shrimp (Crustacea: Anostroca) from Western North America.
''Proceedings of the Biological Society of Washington'' 106 296-304. It is also a federally listed

endangered species An endangered species is a species that is very likely to become extinct in the near future, either worldwide or in a particular political jurisdiction. Endangered species may be at risk due to factors such as habitat loss, poaching and inv ...

of the United States.

Description

''B. sandiegonensis'' ranges 8–16 millimeters in length. It is often mistaken for other branchinectids. For males it can be distinguished by the length of the second antennae and for females by the appearance of the brood pouch.

Distribution

''B. sandiegonensis'' occurs along the coast of Southern California and northwestern Baja California, with its distribution centered in

Ecology and behaviour

It exclusively lives in a vernal pool habitat. It has been identified at 137 vernal pool complexes, many of which have since been extirpated. Others, however, have been restored and preserved, and the shrimp has been reintroduced into appropriate pool habitat. Each pool "complex" consists of several vernal pools supported by a collective

watershed Watershed is a hydrological term, which has been adopted in other fields in a more or less figurative sense. It may refer to: Hydrology * Drainage divide, the line that separates neighbouring drainage basins * Drainage basin, called a "watershe ...

, a crtical component of the vernal pool system. Vernal pool complexes vary in size, from larger interspersed pools to smaller groups of pools, each pool spaced out from another by several meter lengths. ''B. sandiegonensis'' appear during the rainy season from January to March, where vernal pools become filled with water and egg hatching begins. The cycle of hatching occurs across 7 to 14 days, where fairy shrimp hatch and mature to become full grown adults.

Conservation

In the late 1900s, soil landscapes that supported vernal pools were significantly reduced due to human causes, resulting in fewer vernal pool habitats. ''B. sandiegonensis'' was officially listed by the U.S. Fish and Wildlife Service as an endangered species in 1997. Cited reasons include

habitat destruction Habitat destruction (also termed habitat loss and habitat reduction) is the process by which a natural habitat becomes incapable of supporting its native species. The organisms that previously inhabited the site are displaced or dead, thereby ...

due to urban development and changes to vernal pool

hydrology Hydrology () is the scientific study of the movement, distribution, and management of water on Earth and other planets, including the water cycle, water resources, and environmental watershed sustainability. A practitioner of hydrology is calle ...

. ''B. sandiegonensis'' has also been the subject of several studies on

population genetics Population genetics is a subfield of genetics that deals with genetic differences within and between populations, and is a part of evolutionary biology. Studies in this branch of biology examine such phenomena as adaptation, speciation, and pop ...

in an effort to better understand the fairy shrimp itself and the effects of habitat loss. A study on 50 vernal pools from 23 vernal pool complexes found that genetic differentation among ''B. sandiegonensis'' varies significantly, concluding that each complex needs to be viewed as a distinct management unit in order to strengthen conservation efforts. Recent advances in research have also improved identification of ''B. sandiegonensis'' from other hybrids or species whose range overlap with it. Using eDNA testing, UCLA researchers have established a method to identify ''B. sandiegonensis'' from water samples without needing to directly sample individual fairy shrimp. The method was shown to be effective in distinguishing ''B. sandiegonensis'' from a similar generalist species ''Branchinecta lindahli'', however more studies are needed to confirm whether it is effective for distinguishing hybrids. Improving identification of ''B. sandiegonensis'' will help tracking efforts across vernal pool complexes.

References

External links

IUCN Red List of Threatened Species
— ''all species'' {{Taxonbar, from=Q4020306 sandiegonensis Freshwater crustaceans of North America Crustaceans of the United States Fauna of the Baja California Peninsula Fauna of California Natural history of Baja California Natural history of San Diego County, California Taxonomy articles created by Polbot ESA endangered species Crustaceans described in 1993