Amphibians
San Marcos Salamander
Eurycea nana · also called San Marcos salamanders
Tucked among dense aquatic vegetation at the headwaters of the San Marcos River, a San Marcos salamander goes about its entire life within sight of the exact spring outflow it was born in, a species whose whole existence depends on water rising from a single, uninterrupted source.
Overview
The San Marcos salamander, Eurycea nana, is a tiny, fully aquatic salamander known only from San Marcos Springs in Hays County, Texas. Its extraordinarily small size and complete dependence on one spring system make it both one of the more diminutive members of its genus and one of the more vulnerable amphibians in Texas.
A life entirely within sight of its own spring
Unlike species that can disperse across a wider stream network if conditions change, the San Marcos salamander has nowhere to go beyond the springs it was born in, its entire population rising or falling with the health of one specific water source.
Status
Vulnerable — confined entirely to San Marcos Springs, sensitive to any disturbance affecting spring water quality or flow.
San Marcos Salamander: common questions
How rare is the San Marcos salamander?
The San Marcos salamander is known only from San Marcos Springs and its immediate outflow habitat in Hays County, Texas, an extraordinarily narrow range confined to a single spring system, which is why the species is federally listed as threatened despite appearing locally common within that very small habitat.
How small is the San Marcos salamander?
The San Marcos salamander is notably small even compared with several of its already small Eurycea relatives, rarely growing beyond a few centimetres in total length, making it one of the more diminutive members of its genus.
Why is the San Marcos salamander considered a good indicator species?
The San Marcos salamander is highly sensitive to changes in water clarity, temperature, and flow at its spring habitat, meaning a healthy population signals good overall water quality within the Edwards Aquifer system that feeds San Marcos Springs, while a decline can serve as an early warning of broader aquifer problems.
What threats does the San Marcos salamander face?
Because the San Marcos salamander depends entirely on San Marcos Springs, threats such as groundwater pumping, drought, recreational disturbance from swimmers and boaters, and invasive species introduced into the springs all pose a direct risk, since the species has no alternative habitat anywhere else to retreat to if conditions decline.