Stygobiont Diversity in the San Marcos Artesian Well and Edwards Aquifer Groundwater Ecosystem, Texas, USA

Abstract

The Edwards Aquifer and related Edwards-Trinity Aquifer of Central Texas, USA, is a global hotspot of stygobiont biodiversity. We summarize 125 years of biological investigation at the San Marcos Artesian Well (SMAW), the best studied and most biodiverse groundwater site (55 stygobiont taxa: 39 described and 16 undescribed) within the Edwards Aquifer Groundwater Ecosystem. Cluster analysis and redundancy analysis (RDA) incorporating temporally derived, distance-based Moran’s Eigenvector Mapping (dbMem) illustrate temporal dynamics in community composition in 85 high-frequency samples from the SMAW. Although hydraulic variability related to precipitation and discharge partially explained changes in community composition at the SMAW, a large amount of temporal autocorrelation between samples remains unexplained. We summarize potential mechanisms by which hydraulic changes can affect community structure in deep, phreatic karst aquifers. We also compile information on 12 other Edwards and Edwards-Trinity Aquifer sites with 10 or more documented stygobionts and used distance-based RDA to assess the relative influences of distance and site type on three measures of β-diversity. Distance between sites was the most important predictor of total dissimilarity and replacement, although site type was also important. Species richness difference was not predicted by either distance or site type.

Benthic species assemblages change through a freshwater cavern-type cenote in the Yucatán Peninsula, Mexico

“…In Križna jama cave system (Slovenia, 8km long), for example 32 troglobitic aquatic taxa have been recorded so far (Polak and Pipan 2021). In the American continent, San Marcos artesian well and the Edwards aquifer (United States, 10500 km 2 ) display 55 aquatic taxa (Hutchins et al 2021) and Toca do Gonçalo cave (0.5km long) and Areias cave systems (14km long) in Brazil display 22 and 28, troglobitic/stygobitic taxa respectively (Souza and Ferreira 2016).…”

Mammoth Cave: A Hotspot of Subterranean Biodiversity in the United States

“…The terrestrial fauna is particularly diverse-tied for the third richest cave system in the world behind the Postojna Planina Cave System (36 species) in Slovenia and Cueva de Felipe Revention (34 species) in the Canary Islands [226]. With respect to stygobiotic fauna, the Mammoth Cave System ranks second in North America behind San Marcos Artesian Well in San Marcos, Texas (55 taxa, 39 described and 16 undescribed; [227]).…”

Linking Hydrogeology and Ecology in Karst Landscapes: The Response of Epigean and Obligate Groundwater Copepods (Crustacea: Copepoda)

“…Despite an initial impetus in studying the faunal response to the connectivity between the recharge area and the groundwater environments in caves, the phreatic zone has received minor attention, despite the increasing studies of epikarst biodiversity, likely for the intrinsic difficulties in sampling the saturated karst in caves. Most studies of the biodiversity in the saturated karst were developed at the main outlets of such aquifers, karstic springs and boreholes having the primacy [5,20,37,39,40,45,69,70].…”

“…The narrow fissures show a limited flow, are intermittently active through the hydrogeological year and constitute important zones of water and organic matter storage, working as "living chambers" for small-sized invertebrate species [1,5,6,19,20]. In some cases, a karst aquifer may be fed by either the diffuse low-flow infiltration of the epikarst and an allogenic recharge through surface runoff which drains large areas of insoluble rock or low permeability soils where surface water flows directly to adjacent soluble carbonate bedrock.…”