California Freshwater Shrimp

Syncaris pacifica

Description

California freshwater shrimp (Syncaris pacifica ) is a decapod crustacean similar overall in appearance to other North American freshwater (atyid) shrimp. Atyid shrimp can be separated from others based on the lengths of chelae (pincerlike claws) and presence of terminal setae (bristles) at the tips of the first and second chelae. The presence of a short supraorbital spine (above the eye) on the carapace (body) and the angled articulation of the second chelae with the carpus (wrist) separate the California freshwater shrimp from other shrimp found in California.

Adults are generally less than 2.2 in (5.6 cm) in postorbital length (from eye orbit to tip of tail). Females are generally larger than males. Females range from 1.3-1.8 in (3.3-4.6 cm) in length, whereas males range from 1.2-1.5 in (3-3.8 cm) in length.

Shrimp coloration is quite variable. Male shrimp are translucent to nearly transparent, with small surface and internal chromatophores (color-producing cells) clustered in a pattern to help disrupt their body outline and to maximize the illusion that they are submerged, decaying vegetation. Undisturbed shrimp move slowly and are virtually invisible on submerged leaf and twig substrates and among the fine, exposed, live roots of trees along undercut stream banks. Both sexes may darken their bodies uniformly or gradually from top to bottom, but females have the striking ability to darken much more than males. The coloration of females ranges from a dark brown to a purple color. Two observed individuals in Lagunitas Creek were red. In some females, a broad tan dorsal band may also be present. Females may change rapidly from this very dark cryptic color to transparent with diffuse chromatophores, a distinctly different coloration. Neither juveniles nor males have the ability to change color to this degree.

Behavior

The reproductive ecology of the California freshwater shrimp has not been formally described. Reproduction seems to occur once a year. Based upon the reproductive physiology and behavior of other marine and freshwater shrimp, the male probably transfers and fixes the sperm sac to the female shrimp immediately after her last molt, before autumn. It is typical for aquatic crustaceans to copulate during the female's molt just prior to the time of year she becomes egg bearing. The timing of mating was deduced from the presence of ovigerous (egg-bearing) females starting in September. Adult females produce relatively few eggs, generally 50-120. The eggs adhere to the pleopods (swimming legs on the abdomen), where they are protected and cared for during the winter incubation. Although not documented, fecundity (fertility) and egg size may vary based on the size of the female. In studies of other freshwater atyid shrimp, fecundity and egg size increased as the size of the female increased. Young are released in May or early June and are approximately 0.2 in (5.1 mm) in length.

Atyid shrimp (Caridina spp.) in tropical climates tend to breed throughout the year, while those in more temperate areas breed primarily in the summer. Apparently, California freshwater shrimp is one of the few atyid species that breeds during the winter period. The winter (December through March) incubation period is advantageous because the larvae are released during the favorable part of the hydrologic cycle in California, following winter and spring high flows.

Several aspects of the reproductive ecology of the shrimp are unknown. Courtship and mating behavior have not been described. No information is available on the percentage of larvae that reach reproductive maturity. In addition, there is no information as to whether aspects of reproduction are density dependent. The proportion of egg-bearing females of a tropical atyid shrimp has been shown to decline with increased population density.

Newly hatched young (postlarvae) grow rapidly and reach 0.8 in (2 cm) in length by early autumn. Growth slows through the fall, winter, and early spring and then increases through the second summer. A size difference between males and females becomes apparent around this time. Shrimp also reach sexual maturity by the end of their second summer of growth. California freshwater shrimp may live longer than three years; tropical atyid shrimp live only one year.

In aquariums, observed shrimp have remained motionless for long periods, clinging to plants and other objects. Cryptic coloration and limited movements probably reduce their risk of predation. Adults and young have been observed maintaining their positions in midwater through movements of their pleopods and telson (tail). In addition to being able to swim forward and backward, shrimp can "skip" over the water surface when disturbed.

California freshwater shrimp can be described as collectors. They feed upon fine particulate organic matter. Their food sources include 1) fecal material produced by shredders (a functional group that feeds on coarse particulate organic matter); 2) fine organic matter produced by physical abrasion and microbial maceration; 3) senescent periphytic (organisms attached to underwater surfaces) algae; 4) planktonic (free-floating) algae; 5) aquatic macrophyte (large underwater plants) fragments; 6) zooplankton (microscopic animals); 7) particles formed by the flocculation (formation of small loose clusters) of dissolved organic matter; and 8) aufwuchs (a matrix of bacteria, extracellular materials, fungi, algae, and protozoa). Shrimp observed on pool bottoms, submerged twigs, and vegetation seemed to feed on fine particulate matter. Atyid shrimp use their chelae to scrape and sweep detritus (loose organic debris) and small organisms from substrates. Captive shrimp have been observed frequently moving their maxillipeds (front legs) from substrate to mouth. Much of the material ingested is probably indigestible cellulose.

California freshwater shrimp may use visual, tactile, or chemical cues in foraging activities. Shrimp maintained in aquariums scavenge dead fish and shrimp. Captive shrimp have been able to detect and selectively consume commercial fish feeds. Commercially formulated feeds for prawns often incorporate chemoattractants such as glycine, proline, taurine, and trimethylammonium hydrochloride (imparts a fecal odor).

Presumably, shrimp diets change with food availability and age. For example, algae and plant matter increase in the stomachs of grass shrimp by the summer months. However, detritus and insects become more important in the winter. Younger grass shrimp typically had a higher percentage of detrital material in their stomachs than older, larger grass shrimp.

Habitat

Streams inhabited by California freshwater shrimp are part of the Coast Range, a geomorphic province that lies between the Pacific Ocean on the west and the Central Valley of California on the east. The Coast Ranges are composed of marine sedimentary rocks interspersed with metamorphic and igneous materials. Geologically recent erosion of surrounding mountains has resulted in the deposition of variable depths of alluvial materials along the floodplains and valleys of most of the shrimp-bearing streams. Shrimp have been found only in low elevation and low gradient streams. With the exception of Yulupa Creek, shrimp have not been found in stream reaches with boulder and bedrock bottoms. In fact, high velocities and turbulent flows in these streams may hinder upstream movement of shrimp.

The shrimp-bearing streams occur in counties with a Mediterranean climate. Such streams near the town of Sonoma experience average air temperatures of approximately 46°F (7.8°C) in the winter and 70°F (21.1°C) in the summer.

California freshwater shrimp has evolved to survive a broad range of stream and water temperature conditions characteristic of small, perennial coastal streams. The shrimp appears to be able to tolerate warm water temperatures (greater than 73°F [22.8°C]) and no-flow conditions that are detrimental or fatal to native salmonids. Under controlled conditions, juvenile and mature shrimp in an aquarium can tolerate standing water and water temperatures of about 80°F (26.7°C) for extended periods.

Although the laboratory studies indicate that the shrimp can tolerate brackish water conditions—at least for short periods of time—all records of the shrimp are from freshwater reaches in streams. Similarly, other atyid shrimp have demonstrated laboratory tolerance to brackish water but have not been found in similar salinities in nature. The current disjunct distribution of the shrimp and its suspected intolerance to ocean salinities make movement of adults among coastal streams and streams flowing into Tomales and San Pablo bays highly unlikely.

California freshwater shrimp are generally found in stream reaches where banks are structurally diverse, with undercut banks, exposed roots, overhanging woody debris, or overhanging vegetation. Excellent habitat conditions for the shrimp involve streams 12-35 in (30.5-88.9 cm) in depth with exposed live roots (e.g., alder and willow trees) along undercut banks (greater than 6 in [15.2 cm]), with overhanging stream vegetation and vines.

During the winter, the shrimp is found beneath undercut banks with exposed fine root systems or dense, overhanging vegetation. These microhabitats may provide shelter from high water velocity as well as some protection from high suspended sediment concentrations typically associated with high stream flows.

Habitat preferences apparently change during late-spring and summer months. Shrimp are rarely found beneath undercut banks in the summer; submerged leafy branches were the preferred summer habitat. In Lagunitas Creek, Marin County, the shrimp was found in a wide variety of trailing, submerged vegetation. Highest concentrations of shrimp were in reaches with adjacent vegetation consisting of stinging nettles (Urtica sp.) and vine maple. None were caught from cattails (Typha sp.), cottonwood (Populus fremontii ), or California laurel (Umbellularia californica ). Populations of shrimp were proportionately correlated with the quality of summer habitat provided by trailing terrestrial vegetation. However, during summer low flows, shrimp have been found in apparently poor habitat such as isolated pools with minimal cover. In such streams, opaque waters may allow shrimp to escape predation and persist despite the lack of cover. Further research is needed to determine if both winter and summer habitat needs to be provided within the same location or if shrimp can move between areas containing either winter or summer habitat.

Although largely absent from existing streams, large, complex, organic debris dams may have been prevalent in streams supporting shrimp populations. These structures may have been important feeding and refugial (resting) sites for the shrimp because they tend to collect detrital material (shrimp food) as well as leaf litter, which can be broken down by microbial activity and invertebrates to finer, detrital material. In addition, debris dams may offer shelter during high flow events and reduce displacement of invertebrates.

Interestingly, atyid shrimp from other parts of the world display similar habitat preferences. Highest densities of Caridina fernandoi were found in areas underneath branched hairy roots of trees (tree roots afford protection from fish predation); only very low numbers were found on decaying leaves.

Distribution

Prior to human disturbances, California freshwater shrimp is assumed to have been common in low-elevation perennial freshwater streams within Marin, Sonoma, and Napa counties. By the late 1990s this shrimp was found in 16 stream segments within these counties. With the exception of Lagunitas Creek, stream reaches containing populations of shrimp flow through private lands. A substantial portion of Lagunitas Creek flows through the Samuel P. Taylor State Park, managed by the California Department of Parks and Recreation, and the Golden Gate National Recreation Area, managed by the National Park Service. A small segment of Salmon Creek flows through the Watson School historic site, managed by the Sonoma County Department of Parks and Recreation. On East Austin Creek, the Austin Creek State Recreation Area lies immediately upstream of shrimp populations. The most extensive surveys for the shrimp were conducted between 1982-85, when 146 locations were studied.

The distribution of the shrimp can be separated into four general drainage units: (1) tributary streams in the lower Russian River drainage, which flows westward into the Pacific Ocean, (2) coastal streams flowing westward directly into the Pacific Ocean, (3) streams draining into a small coastal embayment (Tomales Bay), and (4) streams flowing southward into northern San Pablo Bay. Many of these streams contain shrimp populations that are now isolated from each other.

Rising sea levels may also explain the presence of isolated populations in streams draining into Tomales Bay and the Pacific Ocean. Before the last sea level rise, the California coastline was 15-20 mi (24.1-32.2 km) westward from where it is situated today. During this period, Stemple, Walker and Lagunitas creeks were probably connected tributaries. The presence of shrimp in Walker Creek could have resulted in their movement to other streams draining into Tomales Bay at that time.

New information regarding the distribution of the California freshwater shrimp has been collected since its listing. The shrimp has been rediscovered in Stemple Creek, and new populations have been found in Keys, Redwood, and Garnett creeks (1994). In addition, U. S. Fish and Wildlife Service (FWS) biologists found a shrimp population in a new location on Austin Creek, upstream of its confluence with East Austin Creek. As evidenced by the recent discovery of shrimp within Keys, Garnett, and Redwood creeks, unsampled and inadequately sampled streams within Marin, Sonoma, and Napa counties could contain additional shrimp populations.

In instances where shrimp are present (historically or currently) in two connecting watercourses, the smaller tributaries generally support more abundant numbers of shrimp than the larger, receiving streams.

Threats

California freshwater shrimp's cryptic coloration and behavioral characteristics imply that predation played an important role in the evolution of the species. All life stages of the shrimp may be prey items for native fish. Other aquatic vertebrate predators may include western pond turtles, salamanders, and newts, which are probably present throughout many of the streams. Although western pond turtles are opportunistic generalists, their diet usually consists of small-to moderate-sized invertebrates. They are able to consume water-column invertebrates through a form of gape-and-suck feeding and may presumably use this technique to consume shrimp as well.

Several features of the shrimp's distribution and life history make it vulnerable to extinction. Existing shrimp distribution within streams is not continuous and is often along short distances. The few streams that historically supported the shrimp were permanent, low gradient streams in just three counties. Through geologic and climatic changes, shrimp populations in coastal streams (such as Salmon Creek, which may have been formerly connected to other streams) are now isolated by inhospitable reaches of sea water. As previously noted, adult shrimp are unable to effectively adjust internal body fluids at high salinities and presumably have lost the ability to persist in sea water. Therefore, local extinctions in streams draining to saline waters may prevent recolonization by natural means.

Furthermore, the shrimp does not have life-history characteristics that favor quick recovery following disturbances. The shrimp has relatively low fecundity, is believed to reproduce only once a year, and maturation requires over a year of growth.

The freshwater shrimp is threatened by several types of human activities, many of which operate synergistically and cumulatively with each other and with natural disturbances (e.g., floods and droughts). Factors associated with declining populations of shrimp include degradation and loss of its habitat through increased urbanization, in-stream gravel mining, overgrazing, agricultural development and activities, impoundments, water diversion, water pollution, and introduced predators. Shrimp populations in most streams are threatened by more than one factor. Although there have been no new threats to the shrimp since its listing, some of the factors that led to its listing have intensified.

Conservation and Recovery

The U. S. Army Corps of Engineers, which must issue permits for the construction of temporary dams, is now required to ascertain the impact of these dams on the habitat of the freshwater shrimp.

This species was listed as endangered by the State of California in 1980, and the California Department of Fish and Game has sponsored a significant amount of research on the ecology and the distribution of the freshwater shrimp. The Soil Conservation Service and the Coastal Conservancy are working with landowners along Salmon and Blucher creeks to develop conservation measures for the shrimp.

In the meantime, schoolchildren are getting into the act as well. One of the FWS's most unusual Partners for Wildlife projects evolved near the small town of Two Rock in a coastal dairy-producing region of Sonoma County in northern California. In 1993 the fourth grade class of Brookside School in the city of San Anselmo began discussing the plight of endangered species. The students' concern about the loss of wildlife led them to take action by "adopting" the California freshwater shrimp, forming a "Shrimp Club" and lobbying, raising money, and sending out information packets to educate the public, legislators, and area farmers about the importance of shrimp conservation.

Working with local dairy farmers, the students also rehabilitated portions of Stemple Creek by (1) fencing off parts of it, (2) planting native riparian trees, shrubs, and native perennial grasses on the banks, and (3) devising a system that allowed cattle to cross from one pasture to another without entering the creek. An estimated 4,000 ft (1,219.2 m) of Stemple Creek was enhanced by the school project, and the quality of shrimp habitat has improved markedly.

Contact

U. S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
Eastside Federal Complex
911 N. E. 11th Ave.
Portland, Oregon 97232-4181
(503) 231-6121
http://pacific.fws.gov/

References

Eng, L. L. 1981. "Distribution, Life History, and Status of the California Freshwater Shrimp, Syncaris pacifica. " Endangered Species Special Publication 18-1, Sacramento.

Hedgpeth, J. W. 1975. "California Fresh and Brackish Water Shrimps, with Special Emphasis to the Present Status of Syncaris pacifica. " Report. U. S. Fish and Wildlife Service, Portland.

Serpa, Larry. 1996. "The California FreshwaterShrimp." Tideline summer issue.

Strait, Daniel. 1996. "A Shrimp Spawns Partnership." Endangered Species Bulletin 21: 1.

U. S. Fish and Wildlife Service. 1977. "Draft: California Freshwater Shrimp Recovery Plan." U. S. Fish and Wildlife Service, Portland. 87 pp.