Adaptation of Aquatic Species

The Blanco River’s instream flow is a major factor in influencing adaptation of aquatic species.  As a consequence of long hot summers with high temperatures, annual evapotranspiration exceeds annual precipitation (PDF) and produces intermittent flows. The high temperatures and low flows cause increased dissolved oxygen rates (D.O.). Erratic precipitation tends can occur as localized thunderstorms cause conditions to morph from dry to flood conditions within hours.

Photo by AquaticInsect.net

Some adaptation of aquatic invertebrates (PDF) found specifically in the Blanco River Basin have been observed by biologists:

• Baetid larval mayflies have adapted by shortening “opportunistic” life spans (2 week larval stages) to take advantage of erratic periods water availability.
• Megalopteran Corydalus sa. shortened egg to mature larval stages from 11-12 months to 6-7 months.

Aquatic Adaptations

Found in all three springs the Blanco River Salamander (Eurycea Pterophila) is a possible new species.

Recently discovered in Jacob’s Well and John Knox Ranch, this blind Stygobromid crustacean could possibly be a new species.

Fern Bank has many species of interest, including an endangered riffle beetle (Heterelmis sp.).

Heptagenid mayfly has a flat body design for fast currents.

Isonychiidae family of mayflies have a hydrodynamic body form for high flows during flood events.

Family Heptageniidae mayfly larvae are able to withstand high flows due to body form and low dissolved oxygen condidtions through external gills.

External gills (for low dissolved oxygen during drought conditions) of damselfly of the order Coenagrionidae

Stoneflies of the genus Perlesta have evolved drought-resistant life stages to help them persist thru hard times.

Endangered dryopid beetle (Stygoparnus sp.) found at Fern Bank.

Megalopteran Corydalus sa. shortened egg to mature larval stages from 11-12 months to 6-7 months.

Baetid larval mayflies have adapted by shortening “opportunistic” life spans (2 week larval stages) to take advantage of erratic periods water availability.