Branchinecta sandiegonensis

Previously misidentified as Branchinecta lindahli (see Eriksen and Belk, 1999).

Limited to the southern California coastal mesa system, an area with significant pressure from urban and industrial development. Vast areas of habitat have been eliminated historically by conversion but restoration and management and a better awareness, plus federal listing and designation of critical habitat have alleviated past declines and populations appear to have stabled somewhat.

Limited to the southern California Coastal Mesa system in Orange and San Diego counties, and adjacent northwestern Baja California, Mexico (USFWS, 1994; Eriksen and Belk, 1999).

Is present in fewer than 70 vernal pools within 11 vernal pool complexes in San Diego County (USFWS, 1994). Unknown how many in Mexico. Number of pools now appears to be around 137, up from 25 when federally listed, but it is believed these are not range expansions, simply pools missed previously due to inadequate survey effort (USFWS, 2008).

From USFWS (2008):
Development is the greatest threat to the species across its range. The growth rate of the human population and associated urban and road development in southern California and northwestern Baja California is equal to or exceeds that of any other region in California and San Diego is one of the fastest growing counties in the nation (adjacent counties of Riverside and Orange are expected to grow very rapidly as well). Development of border security and associated infrastructure also threatens the species along the international border; which could have direct impacts to fairy shrimp habitat, i.e., destruction of vernal pools or their watersheds, and isolation of pools and fragmentation of pool systems; development can also cause alterations in the hydrology of adjacent pools. There are currently development proposals in place that would partially impact another 24 complexes (approximately) occupied by the fairy shrimp but it is expected that impacts will be minimized by imposing conservation measures along the way. Designation of critical habitat and vernal pool restoration have lessened development pressure. Fragmentation and isolation and associated impacts to hydrology continue to threaten the species throughout its range. Development within a vernal pool watershed can alter the timing, temperature, frequency, and length of inundation of nearby vernal pools; and persistence of this species is dependent on maintaining stable hydrology. Modifications to the uplands surrounding a vernal pool (e.g., grading cuts) can negatively affect the pool's hydrology by accelerating the flow of water into or out of the subsoil, even if such modifications occur outside the pool's surface watershed. Although initially considered a threat, destruction of pools by agriculture has largely been mitigated and is no longer considered a substantial threat. This is also the case for limited livestock grazing, which is also no longer considered the threat it once was. Human disturbance (trampling and vehicle traffic) is a minor threat in small portions of the range. Another threat is invasion by non-native plants including two nonnative wetland grasses: Agrostis avenacea (Pacific bentgrass) and Polypogon monspeliensis (annual rabbits foot grass). These invasives can overtake pools and decrease the number of days of inundation following rain events so pools no longer provide suitable fairy shrimp habitat. Threats of military activities originally identified in the recovery plan (USFWS, 1998) have largely been alleviated by better management practices and partnerships with military bases to better protect the species on military lands. Hybridization and competition with the versatile pool fairy shrimp, Branchinecta lindahli, is also a threat, but only in a few locations of disturbed pools where the species overlap. Herbicide and pesticide use is assumed to be a threat but overall impacts are not well known. Other pollution from runoff and rainwater may also threaten portions of the range. Dumped trash and other litter may decrease water quality as materials dissolve or decompose. Dumped material can also fill pools leaving little or no space for water to collect, or cover the bottom of pools, preventing larvae hatching from cysts from moving from the soil into the water column. Drought was noted in the listing rule as a stochastic (random or unpredictable) event that could have drastic affects on the species given its fragmented and restricted range. As such, climate change is now considered a potential threat. Climate change has the potential to adversely affect the fairy shrimp through changes in vernal pool inundation patterns and consistency. The exact effects are not known but are postulated, based on current climate change models, to be deleterious. Although fire was initially considered a substantial threat, the greater number of newly discovered populations helps alleviate the catastrophic effect fire would have on a single or few closely spaced occurrences. More information is needed on the impacts of fire on newly hatched fairy shrimp.