Chapter 3 - Natural Resources - Marine Corps Base Camp Pendleton

MCB Camp Pendleton, California
MCBCP
Camp Pendleton contains three of the remaining 19 drainage basins where arroyo toads are
reasonably believed to be extant: the Santa Margarita, San Onofre, and San Mateo (Figure
3-30). It is likely that some of the largest remaining populations of this species occur on
Camp Pendleton (Holland & Goodman 1998a). For detailed information on the arroyo toad
and its management on Base see Appendix F, Section F.1. Distribution of arroyo toads on
Camp Pendleton are areas identified as believed to be required by the USFWS for recovery
of the species in the recovery plan (USFWS 1999a).
3.2.4.14. Riverside Fairy Shrimp (Streptocephalus woottoni)
FIGURE 3-32. RIVERSIDE FAIRY SHRIMP
Riverside Fairy Shrimp (Streptocephalus
woottoni) are free-swimming filter feeder
crustaceans, which hatch from dormant cysts
once hydrated under specific environmental
conditions. Mature male Riverside fairy
shrimp are approximately 0.5 to 1.0 inches
long and the females are approximately 0.5
to 0.87 inches in total length (USFWS 2005).
Riverside fairy shrimp generally occur in
groups of vernal pools (aka IEW) referred to
as vernal pool complexes, and are typically
visible from January to March; however, the
hatching period may be extended in years of
late rainfall (USFWS 2008h). Vernal pool
complexes tend to average between 5 and 50
(PHOTO SOURCE: C. BROWN, USGS)
vernal pools, although some contain as few as
two vernal pools and others contain several
hundred vernal pools (complexes containing Riverside fairy shrimp often contain only 1 or
2 pools; however, on MCB Camp Pendleton and Otay Mesa in San Diego County,
complexes generally contain many pools). Vernal pools within a complex are generally
hydrologically connected, such that water flows over the surface from one pool to another,
and/or water flows and collects belowground such that the soil becomes saturated with
water, thus filling the vernal pool (USFWS 2008h). For this reason, vernal pool complexes
are best described from a watershed perspective (USFWS 2008h). The vernal pool
watershed includes all areas around a vernal pool complex needed to collect rainfall and
adequately fill the vernal pools within the complex. Vernal pools begin to fill following
the onset of fall and winter rains and may remain hydrated until April or May. Some pools
in a complex have substantial watersheds that contribute to filling the vernal pools, while
others fill almost entirely from rainfall (USFWS 2008h). Additionally, subsurface inflows
from surrounding soils may be an important factor in filling some vernal pools (USFWS
2008h). Riverside fairy shrimp are restricted to dilute vernal pools, having relatively low
sodium (Na+) concentrations (below 60 millimoles per liter), low alkalinity (below 1000
milligrams per liter), and neutral pH (near 7) (USFWS 2008h). Riverside fairy shrimp are
unable to regulate their internal ion levels and mortality increases at higher Na+
concentrations and alkalinity (USFWS 2008h).
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