The Ecology of Virginia Caves

Caves are a unique habitat. There is no light, so animals are far more common than plants in a cave.

The food chain for animals that live exclusively in a cave is based on the little bit of detritus that washes in, or on the animals that feed outside the cave; chemoautotrophic production is minimal in Virginia. Bats import food, creating great mounds of guano underneath their roosting sites far from where sunlight can reach. Various forms of life from bacteria to cave crickets can live on the energy provided by that food source.

Most commercial cave tours involve walking along a paved trail, looking at formations illuminated with lights hidden behind rocks or rock-colored shades. If the lights are left on long enough each day, then algae spores can germinate and grow on the cave formations in the moist environment. The chlorophyll used by the algae to photosynthesize food from the artificial light adds an unnatural green color and texture to the cave formations.

In Virginia, caves are usually very moist environments, and too dark for animals to enter very far (except for bats, who rely upon a form of sonar rather than eyes to navigate without light). Salamanders, fish, and insects are protected against predators in a cave, making them an attractive habitat.

"Facultative" cave dwellers, such as a raccoon or human hunters in colonial days looking for shelter from a rainstorm, use caves when convenient. "Obligate" cave dwellers (troglobites) are those animals that have evolved to the point where they are no longer able to survive outside the cave, sometimes because they have become blind. Food resources are very limited in a cave, so any reduction in metabolic requirements will enhance survival. The Lee County cave isopod has evolved so it does waste energy growing and maintaining eyes, when a cave is always pitch black...

Caves also provide a steady temperature, reflecting the average temperature of the area. Only near the entrance of a cave will the temperature change between day and night, and with the seasons. Virginia caves are about 54-56 degrees, every day, every hour. The one commercial cave in North Carolina, Linville Caverns, is always 52 degrees. It is located south of Virginia but at a higher elevation in the mountains, so its average temperature is cooler.1

Caves are not always a static environment; they can change dramatically at times. A summer thunderstorm can result in a rush of water into a cave, importing leaf debris, raising the temperature, and even drowning bats and breaking cave formations if the cave fllods completely. (WARNING: cavers can also be caught and drowned. Beware of entering wild caves if rainstorms are likely in the area. While underground, people inside a cave will not hear thunder and know when to head back.)

Caves are vulnerable to pollution from the surface. In The Cedars karst region of Lee County, roughly 75% of the water reaching the Powell River travels as groundwater for at least a portion of that journey. Whatever was on the surface - manure from wildlife and cattle, hydrocarbons from highways, pesticides from agricultural operations, etc. - can be carried down into cave systems.2

Contaminants and nutrients introduced into the groundwater from surface aplication of fertilizer, from septic system leach fields, or from stormwater ditches designed to flow into sinkholes can reach the cave and affect the sensitive biological balance. Caves can suffer if the perception is "out of sight, out of mind" regarding waste disposal. Until 2001, the highway maintenance facility for the Virginia Department of Transportation in The Cedars karst region (Jonesville, Lee County) channeled its stormwater runoff directly into a sinkhole.3

In the 1980's, water seeping through piles of sawdust (leachate) from a local sawmill and flowing into Thompson Cedar Cave had very low levels of dissolved oxygen. The pollution appeared to eliminate the cave's local population of the Lee County Isopod (Lirceus usdagalun), which was listed as an endangered species in 1992. After most of the sawdust was removed, water quality improved. Biologists rediscovered the species within the cave in 2002, presumably after survivors in upstream refugia expanded their range into the restored habitat.4

Preservation of the Madison Cave isopod (Antrolana lira) in the Shenandoah Valley faces a similar requirement to conserve the quality of groundwater. The Madison Cave isopod has been fund only where fissures link the surface to the groundwater table. As described in the Final Recovery Plan:5

Urban and agricultural development threatens the quality of its groundwater habitat and thus its survival... The Madison Cave isopod appears to have low reproductive potential, and the small population size at most of its sites indicates that it is highly sensitive to disturbance.

scientists can access some caves on Cedar Creek (Frederick County) via kayak, where the surface/groundwater connection is obvious
scientists can access some caves on Cedar Creek (Frederick County) via kayak, where the surface/groundwater connection is obvious
Source: US Geological Survey (USGS), Valley and Ridge, Piedmont, and Blue Ridge Aquifers

References

1. "Tips for Visitors," Linville Caverns, http://www.linvillecaverns.com/planyourvisit/tipsforvisitors.html (last checked August 3, 2014)
2. "Lee County Cave Isopod (Lirceus usdagalun) Recovery Plan," US Fish and Wildlife Service, September 1997, p.8, http://www.fws.gov/ecos/ajax/docs/recovery_plan/970930c.pdf (last checked August 3, 2014)
3. "Lee County Cave Isopod (Lirceus usdagalun) 5 Year Review: Summary and Evaluation," US Fish and Wildlife Service, Summer 2008, p.6, http://www.fws.gov/northeast/EcologicalServices/pdf/endangered/LeeCountyCaveIsopod.pdf (last checked August 3, 2014)
4. "Sometimes It's the Little Things that Matter," Endangered Species Bulletin, US Fish and Wildlife Service, Fall 2007, p.14, http://www.fws.gov/endangered/news/pdf/ES_Bulletin_09-2007.pdf (last checked August 3, 2014)
5. "Madison Cave Isopod (Antrolana lira) Recovery Plan, US Fish and Wildlife Service, September 30, 1996, http://ecos.fws.gov/docs/recovery_plan/960930d.pdf (last checked August 3, 2014)

the Lee County isopod is not charismatic megafauna like a grizzly bear, but the first rule of environmental management is to save all the pieces
the Lee County isopod is not charismatic megafauna like a grizzly bear, but the first rule of environmental management is to "save all the pieces"
Source: Virginia Tech Extension Service, Endangered Species and Pesticide Regulation


Caves and Springs in Virginia
Virginia Geology
Virginia Places