Longitudinal patterns in stygobiont distribution in the hyporheic zone of the karst spring-fed San Marcos River, Texas, USA

Authors

• Kenneth Sparks
• Benjamin F. Schwartz, Texas State University - San Marcos
• Safra Altman
• Kathryn E. Perez, The University of Texas Rio Grande ValleyFollow
• Zoey B. Chanin, Texas State University - San Marcos
• Caroline Mierzejewski
• Benjamin T. Hutchins, Texas State University - San Marcos

Document Type

Article

Publication Date

7-14-2026

Abstract

Groundwater-obligate taxa (stygobionts) exhibit variable degrees of habitat specialization, ranging from those restricted to single micro-habitats to generalists occurring in a broad range of habitat types. The karstic Edwards Aquifer is the most biodiverse and well-studied groundwater habitat in the continental United States, but some Edwards Aquifer-associated species also occupy the hyporheic zone of rivers downstream from karst. The goals of this research were to 1) assess the potential of the off-karst hyporheic zone as habitat for ‘karst’ species and 2) to determine how stygobiont richness, diversity, and abundance related to distance from karst in the hyporheic zone of a spring-dominated river system. We enumerated stygobionts and quantified environmental characteristics for 55 samples from 11 sites in the San Marcos River between 3 and 140 river kilometers downstream from the rivers’ spring source. Linear mixed effects models and variance partitioning were used to investigate relationships between stygobiont assemblage metrics and environmental parameters (distance from karst, temperature, dissolved oxygen, and hydraulic conductivity). Stygobiont richness and diversity were significantly affected by distance from karst. Stygobiont richness and abundance were significantly affected by hydraulic conductivity. In richness and diversity models, predictive power was low, and additional environmental variables were significant in all models. This study demonstrates that stygobiont communities in the hyporheic zone can be structured by both local environmental conditions, via habitat filtering, and to a lesser extent, by spatial effects (i.e., proximity to source populations in adjacent aquifers). Furthermore, habitat specificity is poorly characterized for stygobiont taxa, inhibiting effective conservation planning and implementation.

Comments

Copyright: This is an open access article distributed under the terms of the CC0 Public Domain Dedication.

Recommended Citation

Sparks, Kenneth, Benjamin F. Schwartz, Safra Altman, Kathryn E. Perez, Zoey B. Chanin, Caroline Mierzejewski, and Benjamin T. Hutchins. "Longitudinal patterns in stygobiont distribution in the hyporheic zone of the karst spring-fed San Marcos River, Texas, USA." Subterranean Biology 57 (2026): 65-89. https://doi.org/10.3897/subtbiol.57.186957

Publication Title

Subterranean Biology

DOI

10.3897/subtbiol.57.186957