by Laurie Dries
The Edwards Aquifer contains numerous intermittent and perennial springs throughout that are home to several species of solely aquatic, perennibranchiate (“always gilled”) Eurycea salamanders. Two of these species have two of the smallest known ranges of any vertebrate species, residing only in the complex of springs known as Barton Springs. Eurycea sosorum, the Barton Springs Salamander, inhabits the surface and immediate subsurface habitat (epigean) of Parthenia Spring (in Barton Springs Pool), Eliza Spring, Sunken Garden, and Upper Barton Spring. Eurycea waterlooensis, the Austin Blind Salamander, inhabits the deeper subterranean habitat beneath the surface of Parthenia, Eliza, and Sunken Garden. Both species require clean, cool, flowing, spring water to thrive; they are stream salamanders, not pond salamanders. The small range sizes, threats to quantity and quality of water emanating from the Barton Springs complex, and harm imposed by cleaning and maintenance of Barton Springs Pool are the main reasons E. sosorum was added to the federal list of endangered species in 1997, and E. waterlooensis was added to the list of candidate species in 2002.
From 2003 through 2008, abundance of E. sosorum had been increasing in all of the spring sites, with periods of reproduction and high number of juveniles and young adults, particularly in Eliza Spring. A more stream-like habitat was reconstructed in Eliza Spring in 2003, ultimately resulting in an increase in average number of salamanders from 9 (1995 – 2002), to 460 (2004 through 2008). There were similar increases in salamander abundance in Parthenia Spring in response to habitat improvements.
Unfortunately, the drought of 2009 took its toll on this species. Salamander abundance in all spring sites dropped to an average of 160 in Eliza Spring, 29 in Parthenia Spring and down to 0 in Sunken Garden. Although the drought broke in late 2009, populations of E. sosorum are currently still recovering from its effects. Drought affects salamanders directly by reducing the amount of oxygen in the water available for respiration. During drought, the volume and rate of water exiting the aquifer, known as discharge, decreases and, as discharge decreases, so does concentration of oxygen dissolved in that water. The consequences of lower oxygen concentration for salamanders are twofold. One, salamanders are at risk of dying because there isn’t enough oxygen to breathe, and two, salamanders stop reproducing because they lack metabolic energy to produce eggs. These effects were evident in the decreases in abundance of salamanders at all three perennial spring sites, Eliza Spring, Sunken Garden, and Parthenia Spring in Barton Springs Pool. For several months, adult abundance was less than 200 in Eliza Spring, less than 20 in Parthenia Spring, and 0 in Sunken Garden. Of these salamanders, nearly none were juveniles. Although the drought broke with rainfall in October of 2009, and Barton Springs’ discharge has been above average for 11 months, salamander abundance has not increased yet; it has remained steady. However, we are finding a few juveniles in Eliza and Parthenia Springs, suggesting some salamanders have begun to reproduce. Since salamander abundance sometimes lags behind increases in aquifer discharge, we hope that we will see higher numbers of both adult and juvenile salamander counts as favorable aquifer conditions continue.