Even though Barton Spring Salamanders have been observed in their natural habitat for the last fifty years, it was not until 1993 that E. sosorum was formally declared a separate species. In the Central Texas area other Eurycea salamanders such as E. neotenes and E. nana are in similar positions such as E. sosorum in that they are extremely environmentally sensitive organisms, limited to one or two populations, which makes them vulnerable to extinction. One major environmental disaster in any of the watersheds that feed the Edwards aquifer (that in turn feeds the springs where these salamanders live) could possibly eliminate the already dwindling populations. An interesting sidenote is that the species name of Eurycea sosorum came from Austin legislation during the early 1990's, known as Save Our Springs (S.O.S.), in regards to increasing environmental protection over Barton Springs. (Rogers 1997; Petranka 1998; Bishop 1967; Chippindale et al 1993)
Barton Springs salamanders have been proclaimed an endangered species by the U.S. Fish and Wildlife Service. E. sosorum was first found in Barton Springs during the 1940's, and numbered in the hundreds. However, in the past decade, fewer than 20 specimens were observed over six month periods and none at other times. In addition, the number of dead salamanders found was increasing. The drastic decrease in the E. sosorum population was credited to the decrease in water quality and quantity of the Edwards Aquifer and even more specifically the Barton Creek Watershed which feeds the aquifer. This decline is the result of increased urbanization and environmental pollution. Also, improper cleaning of the Parthenia pool of Barton Springs (used for recreational swimming) drastically disturbed the chemical and physical equilibriums of the salamanders' habitat. In the past two to three years environmental activists have petitioned for environmentally safer ways for cleaning the pool, bringing greatly needed attention to the water quality and quantity issues concerning Barton Springs as well as the Edwards aquifer. (Rogers 1997; Deanna Chamberlain, personal communication)
US Federal List: endangered
IUCN Red List of Threatened Species: vulnerable
Development - Life Cycle: metamorphosis
Since the placement of E. sosorum on the U.S. ESA endangered species list, major restrictions have taken place on the urban development within the main watersheds of the Edwards Aquifer in Austin, TX. (Rogers 1997)
The diet of E. sosorum consists primarily of the small invertebrate Hyalla azteca, an amphipod. E. sosorum also feeds on snails, crustaceans, black worms, leeches and bug larvae. In captivity the salamanders feed on earthworms, brine shrimp, white worms and commercial food pellets. Predators of E. sosorum are small fish and crayfish. (Deanna Chamberlain, personal communication; Bishop 1967; Rogers 1997)
Barton Springs of Zilker Park in Austin, Travis County, Texas. E. sosorum is restricted to and only found in two (Parthenia and Eliza) of the four hydrologically connected pools collectively named Barton Springs. E. sosorum is the only extant salamander species found in these two pools. No evidence exists that indicates E. sosorum is found anywhere else. This means that E. sosorum has the smallest habitat of any vertebrate in the world. (Chippindale et al 1993; Deanna Chamberlain, personal communication)
Biogeographic Regions: nearctic (Native )
E. sosorum prefers clear waters and is mostly concentrated near the spring openings where food supplies are abundant, water chemistry and temperatures are constant and access to surface and subsurface habitats is available. Barton Springs salamanders are also found under rocks and gravel immediately adjacent to main spring outflows and within aquatic vegetation and algae mats. E. sosorum lives in water depths ranging from 0.1 to 5 meters. The springs where the salamanders are found flow year long and remain at a constant temperature of twenty degrees Celsius. E. sosorum in generally not found on exposed on limestone surfaces or in silted areas within the pools. Monthly population counts done by the city of Austin show that the Parthenia pool population may range anywhere from 90 - 150 salamanders and the Eliza pool has an average population of 30 salamanders. (Deanna Chamberlain personal communication; Rogers 1997)
Aquatic Biomes: rivers and streams
The average length of the Barton Springs salamander is 6.35 cm. The organism is small and is known for its fairly small head, reduced eyes (with a golden iris and black mottling), shovel-nosed snout, slender body and elongate limbs. E. sosorum has a very distinctive dorsal coloration known as the "salt and pepper" effect. Dorsal color varies in life from dark through medium gray to purplish gray or gray-brown to yellowish brown to yellowish cream. The varied degrees of blotched and mottled specks are attributed to an irregular mixture of (or lack of) melanophores, iridophores and pigment gaps. Overall, the mottled pattern gives the salamander olive brown specks with a base color of yellowish cream. The presence of silvery-white iridophores enhances the salamanders' luster. Some salamanders appear pale due to the lack of melanophores. The trunk of E. sosorum is finely speckled with melanophores while the ventral surface is creamy to translucent in color. Sometimes the stomach contents, as well as the presence of eggs in females, can be seen through the translucent skin. Dorsally, the limbs of E. sosorum, are unevenly speckled as well as the toes. Ventrally, the limbs are not speckled. In addition the relatively short tail of E. sosorum has an uneven distribution of melanophores. On the ventral surface of the tail the salamander has a narrow, orange-yellow strip from the posterior margin of cloacal vent to the tip. Furthermore, unique traits of barton spring salamanders include: three pairs of brightly-colored, red gills, four fingers on each hand, five toes on each foot and 16 pre-sacral vertebrae. These traits set Eurycea sosorum apart from other Central Texas Eurycea. (Petranka 1998; Deanna Chamberlain, personal communication; Chippindale et al 1993)
Other Physical Features: ectothermic ; bilateral symmetry
Not many details of the reproduction of E. sosorum are known. This is due to the secretive and nocturnal nature of salamanders in general. In the wild, females have been found holding, at the maximum, forty eggs from September through January. It is known that females carry their eggs for a year before depositing them It takes one year for larvae to reach sexual maturity and all sexually mature individuals that have been found have been longer than 22.5 mm. Also in their native habitat, young hatchlings have been found in November, March and April. This evidence suggests that breeding takes place year round. In the wild, no deposited eggs have ever been found or seen. It is believed the E. sosorum may deposit it's eggs in the Edwards Aquifer which feeds the pools where they live. The Edwards Aquifer is a karst aquifer which means that it is very porous. Due to the small size of the salamander this hypothesis could be true. However, in captivity Barton Spring salamanders deposit their eggs on plastic plants in string-like clusters. The eggs are 1.5 mm in diameter and are surrounded by two jelly layers. They are easily observed because of their white color and iridiscent properties.
(Deanna Chamberlain, personal communication; Bishop 1967; Petranka 1998)
As of 1999, in captive-breeding programs, females have deposited eggs twenty times. Of the eggs deposited, larvae only developed twice and none survived to sexual maturity. What has been noted in the embryos is that after 19 days eyes develop and then, after 38 days, limb bud and gill structure is observed.
(Deanna Chamberlain, personal communication)
Key Reproductive Features: gonochoric/gonochoristic/dioecious (sexes separate)
The Barton Springs salamander (Eurycea sosorum) is an endangered lungless salamander.[1] It is endemic to Texas, United States. It was first found in Barton Springs in Austin, but is now also known from other localities in the nearby Travis and Hays Counties.[5][6] Barton Springs is located within Zilker Park which is situated in the Edwards Aquifer in Austin, Texas.[7][4] Eliza Springs, located within Barton Springs, has one of the largest populations of Barton Springs salamanders.[7]
The Barton Springs salamander prefers clear water and are typically found near openings of springs.[8] These salamanders can also be found under rocks or gravel, within aquatic vegetation, and algae.[4] Barton Springs salamanders can live in water depths ranging from 0.1 to 5 metres (0.33 to 16.40 ft).[4] The springs in which these salamanders inhabit flow year-round and retain a constant temperature of around 20 °C (68 °F).[1]
Barton Springs salamanders grow to approximately 6.4 centimetres (2.5 in) in total length and have mottled coloration varying from darkish purple to light yellow on their dorsal side.[4] The variation in coloring is largely due to the presence or lack of melanophores, iridophores, and pigment gaps.[4] The ventral side of the salamander is either a cream or translucent color which allows stomach contents and the presence of eggs to be visible.[4] The ventral side of the tail has a yellow-orange stripe that extends from the cloaca to the end of the tail.[4] They have a fairly small head with reduced eyes and a slender body with elongated limbs that indicate it occupies a semi-subterranean lifestyle.[4][9] On either side of the salamander are three red gills with four fingers on the forelimbs and five toes on the hindlimbs.[4][9] The Barton Springs salamander is an ectothermic species and displays bilateral symmetry.[4][9]
Barton Springs salamanders are dioecious, and females can hold up to 40 eggs at a time.[10][9] The eggs are about 1.5 mm in diameter, surrounded by a jelly-like layer, and are deposited in a cluster on various substrates year-round.[9][10][11] In captivity, Barton Springs salamanders display a tail-straddling walk during reproduction.[11] Spermatophores deposited by males on substrate are stored by the female in a spermatheca. The fertilization of their eggs is consistent with most salamanders, which utilize internal fertilization in which sperm are released onto the eggs as they pass through the female reproductive tract.[11]
Amphibian species worldwide have been in decline due to climate change including but not limited to: increased UV radiation, change in precipitation, and various pathogen outbreaks (chytrid fungus[12] which causes Chytridiomycosis[12]). However, habitat destruction, degradation, and pollution on a local scale have resulted mainly from land and urbanization near the Barton Creek watershed.[8] Due to the species having a small population and the degradation of its habitat, the Barton Springs salamander is vulnerable to extinction.[1] In addition, aquatic vegetation has been shown to be a critical component to the salamander's habitat; their numbers dropped precipitously after the removal of much of the vegetation from Barton Springs and have recovered after habitat restoration programs were implemented. These changes, in turn, affect, among others, water quality/quantity and biological community composition of rivers and water systems in the surrounding environment.[8] The Texas Water Commission has also indicated that the Barton Springs aquifer is the most vulnerable to pollution within the state of Texas.[1] The wide effects of contamination and degradation on these water systems make analyzing their specific sources difficult since the interactions of factors and overlapping effects may occur. Nonetheless, it is important to study these consequences so that future impact on this and other species may be reduced.[13]
Dissolved oxygen (DO) is required at specific levels to maintain healthy aquatic life. To do this, "national ambient water quality criteria"[13] have been set by the U.S. Environmental Protection Agency and measurements have been made since 1969, albeit inconsistently. Hypoxia, a state of reduced oxygen, may hinder embryonic and fetal development as well as decrease oxygen consumption in adults. Apart from prenatal developments, physiological responses may also arise from a lack of oxygen. Some of the known responses include "Increases in heart rate and buccal pumping, behavioral hypothermia, and gill hypertrophy".[13]
Since this species is an obligate aquatic neotene that retains its gills through its adult life, it must absorb oxygen through its gills or skin. However, the method in which it performs this absorption has yet to be determined. One study found that when presented with a low DO level, this salamander increases its body movement. They theorized two explanations for this reaction:
Much of the Barton Springs salamander's life history remains unknown at this time. These salamanders are neotenic and strictly an aquatic species.[4] This species of salamanders typically inhabits surface waters but are also suited to live in subterranean waters when conditions are not suitable at the surface.[4][11] Barton Springs salamanders utilize innate predator recognition and are opportunistic feeders.[11] It appears that they feed primarily on small aquatic crustaceans and planarian flatworms (Dugesia sp.), but can supplement their diet with other items, such as earthworms, snails, leeches, and insect larvae.[11][14]
The species epithet (sosorum) is an acronym for "Save Our Springs Ordinance" (of the City of Austin) although it is widely if erroneously believed to refer to SOS Alliance, a local preservation group[15] combined with a Latin genitive plural ending.[4]
Despite inhabiting an urban area, E. sosorum was not described until 1993.[4] It was put on the federal List of Threatened and Endangered Species in 1997 and was last assessed in 2004 by the IUCN Red List.[14][1] Under the IUCN Red List, the Barton Springs salamander is listed as vulnerable while in federally and within the state of Texas the species is considered endangered.[1] The salamander's listing prevented the City of Austin from cleaning the Barton Springs Pool as it had for 70 years—with bleach. As a result, the City of Austin applied for and was issued an Incidental Take Permit under Section 10(a)(1)(b) of the Endangered Species Act by the U.S. Fish and Wildlife Service in 1998. The permit has a term of 15 years and allows incidental taking of salamanders during pool cleaning and maintenance. In addition, various conservation measures have been developed under the "Barton Springs Salamander Conservation and Agreement Strategy" which was signed in August of 1996.[1] A captive breeding program was also developed for this species as a way to increase the size of the current population.[1] As a mitigation measure, the City offered to direct 10% of revenue generated through pool entry fees into a conservation fund that is used for research and habitat enhancement. Looking forward, the city of Austin has created an advisory team that will continue to review pool maintenance procedures in the salamander's habitat and conduct monthly surveys to assess population size.[8]
The Barton Springs salamander (Eurycea sosorum) is an endangered lungless salamander. It is endemic to Texas, United States. It was first found in Barton Springs in Austin, but is now also known from other localities in the nearby Travis and Hays Counties. Barton Springs is located within Zilker Park which is situated in the Edwards Aquifer in Austin, Texas. Eliza Springs, located within Barton Springs, has one of the largest populations of Barton Springs salamanders.
