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.
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.