Branchinecta lynchi

Depicted in error as Branchinecta coloradensis by Linder (1941)

Despite the extremely wide range of this species, it is federally listed as a threatened species. While it is not as restricted in range as some of the other fairy shrimp, it is not considered abundant at any site (Eriksen and Belk, 1999, call it "an uncommon, common fairy shrimp"), and its habitat continues to be threatened by urban and agricultural development and climate change; although range, overall, has not contracted.

Endemic to the Central Valley, Central Coast Mountains, and South Coast Mountains of California. It ranges from the Vina Plains in Tehama County, through the Central Valley, and south along the Central Coast to northern Santa Barbara County. There are also several disjunct populations on the Santa Rosa Plateau and in Riverside County (U.S. Fish and Wildlife Service, 1992). Note this is the most widely distributed of the California endemic large branchiopods occurring throughout most of the length of California's Central Valley, from the Millville Plains and Stillwater Plains in Shasta County to Pixley in Tulare County with disjunct populations in the Santa Rosa Plateau near Rancho Santa California in Riverside County (Helm, 1998).

At the time of listing in 1994, it was known from 32 loosely described populations (localities lumped to populations) in a range that extended from the Redding and Stillwater Plains area in Shasta County, California, south through the Central Valley to Pixley in Tulare County, and along the central coast range from northern Solano County to Pinnacles in San Benito County, California (occurrences in Shasta- 1, Tehama- 4, Glenn- 1, Butte- 1, Yuba- 1, Placer- 1, El Dorado- 1, Sacramento- 2, Solano- 1, Contra Costs- 1, Alameda- 1, Merced- 4, Madera- 2, Fresno- 2, San Benito- 1, Tulare- 4, San Luis Obispo- 1, Santa Barbara- 1, and Riverside Cos.- 2) (USFWS, 2007). In 1998 the shrimp was discovered in two distinct vernal pool habitats in Jackson County, Oregon, and these occurrences now comprise a disjunct population center in the Klamath Mountains Vernal Pool Region, approximately 130 miles north of the species' previously known range (USFWS, 2006). The known range of was also extended due to its detection in one pool at the Napa Airport at the southeastern edge of the Lake-Napa Vernal Pool Region. It has been located in 605 pools or swales (Helm, 1998) across 27 counties in the Agate Desert, White City, and Table Rocks areas in the Rogue River Valley in Oregon as well as various localities in the Cantral Valley and Coast Ranges of California (USFWS, 2006). Number of actual occurrences probably fewer after the delineation of element occurrences. Since the species' listing, surveys have documented it in several locations along the edge of the range in the Santa Barbara Vernal Pool Region: at several Department of Defense bases (Fort Hunter-Liggett, Camp Roberts, and Vandenburg Air Force Base), near San Luis Obispo, at the Santa Maria Airport, and in an isolated pool on the Los Padres National Forest; while in Western Riverside Co., it has also been discovered at a limited number of additional pools, as well as from several pools at Cruzan Mesa in Los Angeles Co. (new county occurrence records:Calaveras- 4, Colusa- 1, Kings- 2, Monterey- 34, Napa- 1, and Yolo- 4 Cos.) (USFWS, 2007).

The primary threats are elimination and degradation of vernal pool habitat (habitat almost completely gone in Rogue River Valley and 60% lost in Agate Desert) by industrial, urban, and residential development and conversion of grasslands to agricultural fields. (USFWS, 1992; 2006). Some 92 occurrences (27 percent) are threatened by development, and an additional 27 occurrences (7 percent) are threatened by agricultural conversion (USFWS, 2005). In Oregon, the species is threatened by commercial and industrial development, agricultural conversion, and utility projects causing habitat degradation, pesticide contamination from mosquito control and fertilizer runoff, physical barriers to dispersal, human activities such as urban and agricultural development (USFWS, 2006).
From USFWS (2007):
The largest continuing threat to this species is the loss and modification of habitat due to urban development, agricultural conversion, and infrastructure construction, especially along the periphery of urban areas. Cities are rapidly expanding into vernal pool habitat where the shrimp are found. Conversion of vernal pool habitat to intensive agriculture continues to contribute to the decline in vernal pools. Occurrences within road right-of ways are threatened by road maintenance and road-widening activities. Invasive nonnative plants are a threat to natural vernal pool hydrology in a number of lands under public or private conservation management, including the Stone Lake Preserve, Camp Roberts, the Santa Rosa Plateau, and Skunk Hollow vernal pools, and numerous small remnant parcels of vernal pool habitat. The use of mosquitofish (Gambusia affinis) to control mosquito larvae (to prevent the spread of human pathogens) may be an emerging threat for the shrimp as introduced mosquitofish have been shown to significantly reduce fairy shrimp abundance when introduced to pools with active shrimp. Also during the rainy season, juvenile bullfrogs disperse readily into vernal pool complexes from permanent waters and can spend several weeks or more at pools consuming aquatic invertebrates including macro-crustaceans. Use of off-road vehicles (ORVs) poses an unquantified threat to the vernal pool fairy shrimp at specific locations. The introduction of pesticides and other contaminants into vernal pool waters may threaten occurrences of the vernal pool fairy shrimp. Water quality in vernal pools may also be degraded over large portions of the Central Valley due
to pesticide overspray and residues. The runoff and precipitation that fill the pools can include pesticides (i.e., herbicides, insecticides, fungicides). Drought is likely to decrease or terminate reproductive output as pools fail to flood, or dry up before reproduction is complete. Climate change has the potential to adversely affect the vernal pool fairy shrimp through changes in vernal pool inundation patterns and temperature regimes. Loss and fragmentation of vernal pool habitat is thought to decrease dispersal ability. Therefore, species range shifts that may be required by climate change may be more difficult due to factors such as the loss of potential habitat from development, occupation of potential habitat by nonnative species, and lack of appropriate soil substrates. Existing preserves in California may not provide the full range of conditions needed to sustain fairy shrimp during variable climatic conditions (Pyke, 2004; 2005b)