California Freshwater Shrimp

The California freshwater shrimp (Syncaris pacifica ) (fig. 1), a small freshwater shrimp which lives in lowland streams in Marin, Sonoma, and Napa counties, was designated an Endangered species by the California Fish and Game Commission in 1980 (Eng 1981). It is the only surviving member of the genus Syncaris . Its congener S . pasadenae was extirpated by urban development in southern California. Although an aquatic species, S . pacifica is dependent upon riparian vegetation for food and shelter. During fall and winter months, S . pacifica lives among submerged exposed roots beneath undercut banks, where it is protected from downstream displacement during heavy runoff from winter rains. The tree roots not only provide cover for the shrimp, but also reinforce the streambank enabling the undercuts to persist.

Figure l.
The California freshwater shrimp (Syncaris  pacifica ).

The principal riparian plants comprising the shrimps' habitat are alders (Alnus ), willows (Salix ), blackberries (Rubus ), sedges, and ferns. The leafy branches of these plants grow into the water during spring and summer, providing cover and food for the shrimp. The shade provided by the larger trees reduces solar heating of the stream. This shading is especially important during droughts when the shrimp are confined to remnant pools. During spring the shrimp move out from the undercut banks and live on the submerged leafy branches of streamside vegetation. They also utilize the exposed hair-like adventitious roots of alders growing along the stream margin. The submerged leaves and filamentous roots collect detrital material and serve as substrates for bacteria and other decomposers, thus providing a food source for the omnivorous shrimp. Submerged and decomposing leaves may also be consumed by the shrimp.

Habitat degradation has resulted in the extirpation of this species from at least five streams (Hedgpeth 1975). Some longtime residents of the area report that the shrimp once occurred in virtually every stream in the three county area; however, we have records of their existence, historically, in only 10 streams (Eng 1981). Continuing urban and residential development pose threats to streamside vegetation, especially in Sonoma County, one of the fastest-growing counties in the state. Hedgpeth (1968) reported that S . pacifica was extirpated in Santa Rosa Creek by an urban improvement project in Santa Rosa. Livestock grazing continues to be a problem locally, causing loss of riparian vegetation and collapse of streambanks. Construction of summer dams and artificial beaches for recreational purposes has destroyed substantial amounts of shrimp habitat in some streams. Vineyard development has also resulted in the loss of substantial amounts of riparian vegetation. In many cases, the vineyards extend to the stream margin.