Subterranean Fishes of the World

6932

2024

Texas, USA has a long history of groundwater ecology research, and the Edwards Aquifer is a recognized hotspot of stygobiont diversity. The state spans a dozen ecoregions and large precipitation and temperature gradients across an area over 695,000 km2, making it an attractive study area for large-scale biogeographic investigations. Despite this, the hyporheic zone of Texas streams was essentially unstudied prior to 2015. Investigation of Texas hyporheic sites was initiated because of the need for more complete occurrence data for at-risk stygobiont species, and more recently, interest in how groundwater-surface water interaction may influence stream responses to climate change. Since 2015, nearly 200 hyporheic sites across the state have been evaluated, allowing for several novel insights. The effort has spurred renewed taxonomic discovery, resulting in the description of 8 stygobiont species. Multiple taxa previously known only from karst aquifers are now known to also occur in the hyporheic zone. A smaller subset of taxa (e.g., species of Microcerberidae, Asellidae, Parastenocarididae) are apparent hyporheic specialists and reach higher abundances than observed for stygobionts in other Texas groundwater habitats. Proximity to karst and karst features has repeatedly emerged as an important influence on stygobiont diversity in the hyporheic zone at multiple scales. At the reach scale, stygobiont richness is positively correlated with proximity to groundwater upwelling in karstic regions (GLM, R2 = 0.5, p <0.01) and positively correlated with proximity to karst in non-karstic regions (GLM, R2 = 0.4, p < 0.01). At the landscape scale, stygobiont richness is also higher in karst regions than in all other lithologies (GLMM, p < 0.01), and community structure in the hyporheic zone varies in response to basin geology. The reasons for these relationships are uncertain, but we suggest two potential mechanisms related to environmental filtering and dispersal. First, we illustrate that hyporheic zone hydraulic conductivity is higher in karst areas than in non-karst areas (x̅ = 0.09 cm/s vs. 0.05 cm/s, AOV: F = 5.08, p < 0.01). We suggest that hydraulic conductivity, which influences dissolved oxygen, organic matter availability, and solute transport, is an important measure of habitat availability and habitat quality (environmental filtering). Second, we show that hyporheic zone stygobionts are largely a subset of upstream karst aquifer taxa: the nestedness component of β-diversity is marginally higher than turnover (βnestedness = 0.44, βturnover 0.36, t = 1.79, p = 0.08), and HZ communities are always less diverse and nested within aquifer communities. We suggest that the biologically diverse karst aquifers of Central Texas serve as a major colonizer pool for overlying and downstream hyporheic communities (dispersal)

2

26th International Conference on Subterranean Biology and 6th International Symposium on Anchialine Ecosystems: Cagliari 9-14 Sept 2024