Advancing Protection of Subsurface Species: New Tools Demand New Policies

 

Why Protect Caves?

It is no coincidence that caves are home to a wealth of precious history. As one of the earliest forms of shelter, these subterranean domains have provided essential resources and protection against natural elements and predators for over 2 million years (Collen, 2022). Caves continue to teach us more about the cultural, natural, and geological history of the earth and its early inhabitants. 

In addition to opportunities to learn more about the past through artifacts and fossils, the unique conditions of caves, aquifers, and other subsurface ecosystems allow these underground realms to harbor microorganisms, bioactive compounds, and evolutionary secrets yet to be discovered. Research indicates that antimicrobial substances produced by subterranean organisms even spur advancements against diseases like cancer (Zada et al., 2021). Furthermore, these ecosystems sustain life by providing ecosystemic services we are only beginning to understand. 

For humans, aquifers provide drinking water to around half of the global population (Johnson, et al., 2022). In the US, approximately 40-50% of water used daily is sourced from underground environments through either a private well or public distribution system (Johnson, et al., 2022). Amid a growing global population, the sustainable management of groundwater is essential (National Park Service, 2018). 

Caves are also home to numerous species that have uniquely adapted to thrive in their unusual environments, leading to independent evolutionary paths distinct from their surface-dwelling ancestors. These isolated habitats preserve ancient lineages and unexplored biodiversity.

While cave and karst ecosystems are well known to serve a vital role in sustaining life at the surface, there still are vast knowledge gaps around existing subterranean biodiversity and the abiotic and biotic factors that comprise these spaces (Mammola et al., 2021, p. 5). For example, only 22% of California’s known caves (at least 4,600) have been biologically sampled (Id.)

In California alone, at least 366 taxa known to occur in caves have been recorded, including102 troglobites (terrestrial cave obligates), 12 stygobites (aquatic cave obligates), and 32 phreatobites (obligate groundwater forms). Efforts to identify and understand these species have accelerated in recent years (see Elliot et. al., 2017). 

Despite the known presence of unique species, however, the potential presence of caves and other subsurface features are typically dismissed in the context of environmental review and land use planning. Considering the sensitivity and importance of these resources and their ecological processes, reasonable efforts to conduct proper analysis of potential risks should be mandatory for any project involving chemical contamination, natural resource extraction, significant alteration of soils and/or hydrology, or other disruptions to groundwater flow patterns.

Cave Adapted Species

Many animal species depend on subsurface ecosystems for all, or a portion of their life cycles. Animals living permanently in underground dark zones termed troglobites (terrestrial) and stygobites (aquatic) often exhibit troglomorphy, i.e. evolutionary adaptations that enable survival in the specific microclimatic features (illuminance, temperature, humidity) of their subterranean habitats, typically characterized by trophic depletion and other extreme conditions (Bussott, S., - 14 - 2018; Soares, D. and Neimiller, M., 2018). Morphological characteristics common to many troglobitic organisms include reduced or lack of pigmentation and/or eyes, specialized organs to detect vibration, and elongated appendages adapted for sensory movement. 

Eurycea rathbuni

For example, the Texas Blind Salamander (Eurycea rathbuni)—a troglobitic species found only in the Edwards Aquifer near San Marcos, Texas—has adapted to life in complete darkness by using specialized sensory organs rather than relying on vision to detect vibrations and water currents to navigate and hunt. (USFWS 2023, Forestry 2024). The Cave Angel Fish (Cryptotora thamicola)—restricted to limestone cave locations in Thailand—has similarly adapted to its unique underground habitat by losing pigmentation and developing a unique method of locomotion that allows it to climb cave walls and waterfalls, relying on its highly specialized pelvic structure to navigate through its dark environment (Flammang et al., 2016).

Notwithstanding many unknowns, subterranean environments and their biota are said to be inextricably linked to surface processes, and directly affected by anthropogenic disturbances such as agricultural and industrial activities, chemical contamination, and climate change (Mammola et al., 2021, pp. 7-8). 

Given their narrow endemicity, slow population growth, and sensitivity to shifts in environmental conditions, many cave-adapted species are of significant conservation concern (Bendik, et. al., 2021). Effective conservation of subterranean species requires reliable data on the size, distribution and connectivity of populations (Recknagel, H. and Trontel, J., 2019). The loss of subterranean fauna and the ecosystem services they provide resulting from lack of reliable data could lead to detrimental consequences for surface communities - including humans. For example, stygobiont living in aquifers are known to play a key role in water purification and the biodegradation of contaminants and pathogens (Griebler, C. and Avramov, M., 2014). 

Cave Visitors 

Animals that either can (troglophile) or must (trogloxene) enter and exit caves, such as bats, crickets, amphibians, and birds, contribute vital nutrients to cave obligate species and are considered indicators of subterranean ecosystem health (Gillieson, D. et al., 2022). However, these animals can also carry contaminants from the surface into caves. Exposure to toxic chemicals at the surface can lead to significant degradation of subsurface habitats, tragically poisoning these habitats through guano or toxic tissues when death occurs (Schanzer, S. et al., 2022).

For example, Cave Crickets are considered a keystone species in many cave ecosystems due to their essential role in moving nutrients from the surface to the interior in the form of guano.  Because their foraging behavior sustains many organisms dependent on the organic subsidies they provide, monitoring and protecting these species has become a priority for resource managers including the National Park Service (USGS Mammoth Cave 2008). 


Similarly, at least 50 percent of global bat species rely on caves to fulfill critical life history functions including roosting, rearing young, hibernating, and swarming (Tanalgo, K. et. al., 2020, p. 2). As pollinators, seed dispersers, and major consumers of nocturnal insects, bats sustain healthy ecosystems and play a major role in preventing uncontrolled insect population growth, subsequent crop failure, and related economic damage (Reshetiloff, 2017). Thus, protecting cave habitats means protecting bats and ensures that ecosystems remain in balance underground as well as at the surface.

New Technologies for Analyzing Subsurface Ecosystems

With more than 45,000 caves confirmed in the United States alone, new technologies for detecting and analyzing subsurface features provide new opportunities to explore and understand the unknown. For example, Light Detection and Ranging (LiDAR) uses laser pulses to measure variable distances from a reference point, making it easier to map caves with greater ease and detail. Other technologies that have Structure from Motion (SfM), a photogrammetric technique that constructs 3 dimensional models from 2 dimensional images, and advanced imagery, such as aerial photography and satellite imagery, are often used to identify surface features commonly associated with caves. 

While some of these technologies have been around for a while, new and improved ways of using them are constantly being developed to better understand and protect caves.  Over the last few years, LiDAR scanners capable of faster and more accurate scans and portable enough to be operated by a single person have been developed by a number of tech companies around the world.

Law and Policy

Ensuring sustainable use of land and water requires an understanding of the hidden connections between above-ground and underground habitats. Environmental regulations must evolve to mandate that agencies account for potential damage to subsurface ecosystems during impact reviews. As mapping techniques and technologies continue to improve, more comprehensive assessments must be incorporated into decision-making processes to accurately identify and mitigate risks to delicate underground habitats. More specifically, projects involving significant contamination or movement of soil, vegetation, or surface waters should be required to identify subsurface features where adverse impacts are foreseeable. Agencies responsible for implementing environmental review processes and procedures must evolve to appropriately incorporate these expectations.

Policies that encourage water conservation and the reduction of pollutants are also essential. For example, Portland, Oregon's On-site Stormwater Management Program promotes sustainable water practices by incentivizing property owners to manage stormwater on their property. Through the Clean River Rewards program, residents receive discounts on their stormwater management charges by implementing solutions like rain gardens, permeable pavements, and green roofs. These practices reduce runoff, prevent pollutants from entering waterways, and ultimately protect both surface and subsurface ecosystems.

 
 

Sources:

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  14. Schanzer, S., Koch, M., Kiefer, A., Jentke, T., Veith, M., Bracher, F., Bracher, J., & Müller, C. (2022). Analysis of pesticide and persistent organic pollutant residues in German bats. Chemosphere, 305, 135342.  https://doi.org/10.1016/j.chemosphere.2022.135342 

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Lindsey Zehel