Eurycea sosorum Chippindale, Price & Hillis, 1993
Barton Springs Salamander
© 2007 Danté B Fenolio (1 of 4)
Country distribution from AmphibiaWeb's database: United States
U.S. state distribution from AmphibiaWeb's database: Texas
Eurycea sosorum Chippindale, Price and Hillis, 1993
Paul T. Chippindale1
1. Historical versus Current Distribution. Barton Springs salamanders (Eurycea sosorum) were described by Chippindale, Price, and Hillis (1993); the type locality is Barton Springs pool, a spring-fed swimming hole in the city of Austin, Travis County, Texas. This species is known only from the pool and three other springs that are immediately adjacent (Chippindale et al., 1993; City of Austin, 1997; Hansen et al., 1998). The spring outflows inhabited by this species are fed by the Barton Springs segment of the Edwards Aquifer. Eurycea sosorum was first recognized as a distinct, undescribed species by Sweet (1978a, 1984), based on its morphological differentiation from other surface and subterranean species of central Texas Eurycea. Chippindale et al. (1993) also demonstrated that this species is distinct based on morphology and allozymes. Chippindale et al. (2000) support recognition of this species and determined its relationships to other central Texas Eurycea using allozyme and mitochondrial DNA sequence data. Hillis et al. (2001) confirmed the phylogenetic position of this species using additional sequence data. Eurycea sosorum is a member of the "southeastern" subset of the "southern group" of Chippindale (1995, 2000) and Chippindale et al. (2000); this monophyletic group occurs south of the Colorado River in the Edwards Plateau region of central Texas.
2. Historical versus Current Abundance. Little is known of the historical abundance of this species. The first known specimens were collected in 1946 by B.C. Brown from among plants in Barton Springs Pool (Chippindale et al., 1993). Observations by others (summarized by Chippindale et al., 1993) indicate that this species was abundant in the 1960s and 1970s. Considerable evidence (summarized by Chippindale et al., 1993; O'Donnell, 1994, 1997; Hansen et al., 1998; Hillis et al., 2001) indicates that the population underwent a major decline in the 1980s–'90s, probably due in part to cleaning procedures used by the City of Austin at Barton Springs Pool. The City was made aware of the problems in the early 1990s and has since cooperated closely with biologists and conservation agencies to balance the need for pool maintenance with protection of Barton Springs salamanders. Details of the City's actions and the conservation history of this species are provided by Chippindale and Price (2001). Abundance of salamanders appeared to increase substantially following modification of pool maintenance procedures, but the number of individuals located have been highly variable from year to year and the most recent data suggest a decline in numbers in 2000. Considerable concern remains regarding the impacts of human activities on water quality in the Barton Springs Aquifer, summarized by Chippindale and Price (2002).
3. Life History Features.
A. Breeding. Reproduction is aquatic.
i. Breeding migrations. Unlikely to occur.
ii. Breeding habitat. Unknown; a subset of adult habitat.
i. Egg deposition sites. Unknown in the wild; some other spring-dwelling species of central Texas Eurycea are thought to deposit eggs in gravel substrate. In captivity, oviposition has been observed at the Dallas Aquarium and the city of Austin facility. Females appear to deposit the eggs randomly on cobble, gravel, aquatic macrophytes, and even the glass sides and bottom of the aquaria. Gravid females may retain the eggs for periods longer than 12 mo (L. Ables, D. Chamberlain, personal communication). With some gravid females, oviposition does not occur and the eggs are resorbed by the female.
ii. Clutch size. Twenty-nine ovipositions have been reported in captivity as of August 2000. The Dallas Aquarium has reported 24 egg-laying events. Of these, 20 have occurred in one particular tank containing one male and four females. In captivity, eggs hatch in approximately 25–35 d (L. Ables, personal communication). The high mortality rate of small juveniles at the Dallas Aquarium has limited the number of surviving young Barton Springs salamanders to about 50 juveniles (L. Ables, personal communication). The City of Austin has recorded three ovipositions of 29, 26, and 28 eggs with hatch rates of 0%, 27%, and 7%, respectively. Survival rates for the three ovipositions are 0%, 11%, and 4% (City of Austin, unpublished data). The San Antonio Zoo reported one oviposition of 18 eggs and a 0% hatch rate (G. Stettner, personal communication). The USGS's Midwest Science Center reported one oviposition of 29 eggs with a 10% hatch rate (J. Dwyer, personal communication). Clearly, further study is necessary to determine what cues (if any) trigger breeding and what conditions are optimal for development of eggs and young. The City of Austin is currently expanding their captive breeding program, and the facility has been relocated to the University of Texas at Austin campus.
C. Larvae/Metamorphosis. Barton Springs salamanders are paedomorphic, and natural metamorphosis is unknown.
D. Juvenile Habitat. Probably similar to those of adults. City of Austin field studies (unpublished data) indicate that larvae, juveniles, and adults utilize similar substrate types (cobble, gravel, aquatic macrophytes).
E. Adult Habitat. Completely aquatic. Barton Springs salamanders are known only from the vicinity of spring outflows, under rocks and leaves, and in gravel substrate at depths ranging from a few cm to about 5 m. The first known specimens were collected in 1946 among aquatic plants. Water temperature of the spring outflows remains relatively constant at about 20–22 ˚C throughout the year.
A recent study conducted by Alan Plummer Associates, Incorporated (2000), for the City of Austin summarizes water quality conditions at Barton Springs Pool. The analysis was based on City of Austin and U.S. Geological Survey data and concluded the following: (1) no trends of increasing concentration were found for several of the parameters commonly associated with nonpoint source pollution—nutrients, total suspended solids, and pesticides/herbicides; (2) trends of increasing concentrations were found for conductivity, sulfate, turbidity, and total organic carbon; (3) a trend of decreasing dissolved oxygen concentration was identified; and (4) the ratio of total nitrogen-to-total phosphorus was found to vary widely over time (from ≤ 20 to ≥ 100) and no observable trend was identified.
The City of Austin has also conducted contaminated sediment studies and analysis at Barton Springs Pool and sites in Barton Creek above and below the pool. Polycyclic aromatic hydrocarbons (PAHs) were detected in sediment in or near Barton Springs at levels that may have biological effects. High levels of several pesticides were also detected in sediment directly upstream of Barton Springs Pool. These pesticides include aldrin, DDD, DDE, DDT, BHC, endosulfan, endrin, heptachlor epoxide, heptachlor, and lindane. Heavy metals also were detected in sediment at sites in and near Barton Springs. These metals include arsenic, cadmium, chromium, copper, lead, and zinc (City of Austin, 1997).
Barton Springs salamanders appear to be primarily surface dwelling, but may also use subterranean habitat; the extent of their occurrence underground is uncertain (Chippindale et al., 1993). Sweet (1982) provided a comprehensive distributional analysis of the central Texas Eurycea and discussed hydrogeology of the region in relation to salamander distribution.
F. Home Range Size. Unknown.
G. Territories. Unknown.
H. Aestivation/Avoiding Dessication. Unknown.
I. Seasonal Migrations. Very unlikely to occur; recent field studies by City of Austin staff indicate that no seasonal variation occurs for habitat use.
J. Torpor (Hibernation). Individuals have been found active throughout the year.
K. Interspecific Associations/Exclusions. Partially sympatric with the recently discovered Austin blind salamander (Eurycea waterlooensis), which inhabits the subterranean portion of the Barton Springs Aquifer (Hillis et al., 2001). Individuals of this new species occasionally wash out of the spring outflows where E. sosorum occur. Specimens of Eurycea have been collected at Barton Springs Pool, Eliza Spring, and Old Mill Spring. No specimens have been observed at the Upper Barton Springs site (City of Austin, unpublished data). Eurycea waterlooensis is much more closely related to Texas and Blanco blind salamanders (E. rathbuni and E. robusta) than to E. sosorum (Hillis et al., 2001).
L. Age/Size at Reproductive Maturity. Unknown. Average SVL of specimens measured by Chippindale et al. (1993) was 29.2 mm; all animals measured were thought to be sexually mature, but this was only verified for some of the specimens. Maximum size of specimens examined by Chippindale et al. (1993) was 36.5 mm SVL (62.6 mm TL).
M. Longevity. Individuals (still living) have been maintained for over 6 yr in captivity.
N. Feeding Behavior. Prey probably consists mainly of small aquatic invertebrates, especially amphipods (Hyallela azteca), which are abundant in the habitat of this species. Gut analyses have revealed the following prey items: mayfly larvae, midge larvae, ostracods, copepods, physid snails, planorbid snails, and leeches (City of Austin, unpublished data). Captive specimens have accepted amphipods, earthworms, brine shrimp, bloodworms, blackworms, mosquito larvae, and commercial fishfood pellets (Chippindale et al., 1993; L. Ables, D. Chamberlain, personal communication; personal observations). Small larvae have disappeared when kept in aquaria with large juveniles and adults, so cannibalism may occur (L. Ables, personal communication).
O. Predators. Bass and sunfish are known predators (City of Austin, unpublished data; D. Hillis, personal communication). Crayfish have been suggested as potential predators, but most local experts think that they are not major predators.
P. Anti-Predator Mechanisms. Secretive.
Q. Diseases. Unknown.
R. Parasites. Unknown.
4. Conservation. While Barton Springs salamanders were abundant in the 1960s–1970s, they underwent a major decline in the 1980s–'90s, probably due in part to cleaning procedures used by the City of Austin at Barton Springs Pool. Abundance of salamanders appeared to increase substantially following modification of pool maintenance procedures, but the number of individuals located have been highly variable from year to year. The City of Austin has established a captive breeding program for this species, and considerable concern remains regarding the impacts of human activities on water quality in the Barton Springs Aquifer. Barton Springs salamanders have been listed as a Federally Endangered species since 1997 (O'Donnell, 1997).
1Paul T. Chippindale
Literature references for Amphibian Declines: The Conservation Status of United States Species, edited by Michael Lannoo, are here.
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