Phantom Spring is home to two rare and exceptional desert ecosystems. Outside the cave resides a temporally intermittent lake, known regionally as a ciénega, the Spanish term for a spring. Travelers and natives that depended on this source of water named it Phantom Spring Lake because it would appear and disappear with the changing of the seasons. Since this area, much like the rest of Texas, is experiencing the worst drought on record, diminished recharge coupled with increased irrigation has significantly lowered the water level inside the cave. As a result, the ciénega pool outside the cave is now at an elevation 1 meter above the current water level in the cave. This desert oasis would have dried up had it not been habitat restoration performed by the Bureau of Reclamation and the U.S. Fish and Wildlife Service involving pumping of water out of the cave and into the ciénega to maintain it at pre-drought water levels.
Why preserve this already at-risk oasis in the desert? Two endangered species of small fish inhabit the ciénega, the Comanche Springs pupfish Cyprinodon elegans and the Pecos gambusia Gambusia nobilis. Comanche Springs located within the city limits of Fort Stockton, Texas first went dry in 1995 resulting in the loss of the pupfish from this locality. It is now only know from a group of springs around Balmorhea including Phantom Springs. Likewise, the Pecos gambusia was once more widely distributed, but today is only found in springs surrounding Balmorhea.
A rare amphipod, Gammarus hyalelloides, flourishes in the pristine waters of the cienega and is the smallest known amphipod in North America. This amphipod makes up more than 70% if the diet of the Pecos gambusia in Phantom Lake Spring. Due to its limited distribution, Gammarus hyalelloides is listed as a threatened species. Most importantly these organisms are early indicator species of pollution, a “canary in the coal mine” of sorts, in an area where groundwater is often the only source of freshwater.
The second desert ecosystem of Phantom Spring lies within the entrance of the spring. Here underwater cave passage provides a window for cave diving scientists to enter this desert aquifer. High flow and warm waters in the cave indicate that artesian waters deep beneath the desert feed the system. Cave adapted, aquatic invertebrates also known as stygobites, have evolved to survive in this lightless, energy deficient habitat. Due to the fact that no photosynthesis can take place in this cave, stygobitic invertebrates depend on either outside energy sources carried into the cave or microbial communities that create energy from biologically unavailable sources within the cave. One stygobite in particular, the isopod Lirceolus cocytus, thrives just beneath the water level on roots that have penetrated the overlying rock. L. cocytus resembles an underwater termite lacking eyes and pigment, as all truly cave-adapted species do. Commonly known as the Phantom Cave isopod, L. cocytus was named for the river Cocytus, one of the 5 rivers phantoms had to pass over to enter the Greek underworld of Hades. It is unclear whether these isopods feed directly upon the roots or upon a microbial film on the roots. In addition to Phantom Spring Cave, Lirceolus cocytus is also known from Sótano de Amezcua cave in Coahuila, Mexico. The only other stygobitic species known from Phantom Springs is a second isopod, Cirolandes texensis, resembling a rolly-polly without pigment. The diet of C. texensis is also unknown. Interestingly, the genera Cirolandes and Lirceolus have also been reported from other springs in Texas and northern Mexico.
Herein lays the focus of our investigation. Can stygobitic species be used as a genetic tracer to determine the hydrologic connectivity of Texas and Mexico’s aquifers? Currently aquifers on both sides of the border are managed and therefore rationed as separate systems. Imagine two straws protruding from a single glass of water, in the desert. What implications arise if one person (or country) extracts more water from the shared glass? What if wells on both sides of the Rio Grande were in fact drawing from a single aquifer?
In addition to groundwater extraction from municipalities and irrigation, these desert ecosystems are faced with the threat of hydraulic fracturing, also known as fracking. Serving as the primary method to extract petroleum and natural gas from deep shale formations, fracking activity is increasing at a rapid rate in Texas. More than 10 natural gas wells have been reported between Phantom Springs and the nearby town of Pecos. Over a well’s lifetime, it can require up to several million gallons of water. In addition to requiring large quantities of water, fracking fluid is composed of chemical additives including known carcinogens such as benzene, lead, and boric acid. Disposal of fracking fluid often consists of injecting this polluted brine into disposal wells around the area. Migration of fracking fluid poses one of the most common forms of groundwater contamination in areas with high natural gas activity.
The primary objective of this study is to determine the genetic relationship between similar stygobitic species from springs on both sides of the border. These relationships will then be used to create a biogeographic map with the hydrologic connectivity of the areas’ aquifers/aquifer. This investigation is a joint effort between Dr. Tom Iliffe of Texas A&M University at Galveston and Dr. Fernando Alvarez of the Universidad Nacional Autónoma de México (UNAM) in Mexico City. Research funding is provided by a collaborative research grant program between Texas A&M and the Consejo Nacional de Ciencia y Tecnología (CONACyT). Genetic analysis will be conducted on stygobitic species collected from cave passages and spring openings on both sides of the Texas/Mexico border. To date over 100 stygobitic species have been collected for this study from 10 springs in Texas and 2 springs in Mexico.
Figure 1. Distribution of Lirceolus species throughout Texas and Mexico (Lewis, 2001).
Lewis, Julian J. 2001. Three new species of subterranean asellids from western North America, with synopsis of the region (Crustacea: Isopoda: Asellidae). Texas Memorial Museum, Speleological Monographs, 5:1-15.