March 2000 - Volume 61, Issue 3
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In this issue
Missouri Cave Life
A dark, bleak habitat gives rise to some peculiar inhabitants
People visit Missouri caves for a variety of reasons. Some seek opportunities for exploration, photography or geology; others study the organisms associated with cave habitats, a discipline called biospeleology. If you are intrigued by the underground take a trip with us to a typical Missouri cave. The first thing we notice is cool air drifting out of the entrance. If we made our trip during the winter months, the cave air would feel warm, instead. It's all relative. Cave temperatures stay fairly constant throughout the year. Missouri caves typically have an average yearly temperature of approximately 55-58 degrees Fahrenheit.
We occasionally see birds in the entrance zone of the cave. The Eastern phoebe often builds nests here. Vultures often raise their chicks here, too. Birds do not normally enter a cave, they just use its mouth for protection from the weather.
Snakes also use entrance areas. On hot summer days, the cooler air exiting the cave can help cool down a snake's body temperature. Snakes usually do not penetrate too far in, for there is little food deep in the cave.
Woodland plants may live near the mouth of the cave. Mosses and walking ferns may grow in the cooler air and in the low light of the cave entrance.
Entrance areas usually accumulate leaf litter and organic debris that has blown into the cave. Small logs, sticks and bark fragments blow in or float in with rain water. We could find a surprising diversity of small invertebrates in the decomposer community that will break down this organic debris. These are often so small that they are overlooked by most cave visitors (human, that is).
Occasionally we find salamanders in this entrance area, but they also live outside. Perhaps they are taking advantage of the cave's constant temperature, high humidity or prey found in the leaf litter or cave stream. The beautiful cave salamander is orange with black spots distributed over its body. It commonly lives outside of caves, under logs and leaf litter in the forest.
Other salamanders that are fond of caves, but not restricted to them, include the slimy salamander and the long-tailed salamander. None of these animals poses any threat to humans. They feed on small invertebrates they find in the leaf litter or streams. The leaf litter community may contain small millipedes, centipedes, terrestrial isopods, often called pill bugs or roly polys, terrestrial snails, earthworms and a variety of insects. We might see mosquitoes, flies and midges resting on the cave walls. These flying insects are not restricted to the entrance zone of the cave; they might move deeper into the cave, particularly in winter months.
As we move deeper into the cave, the light diminishes quickly. We have reached what biospeleologists call the twilight zone. Few photosynthetic plants can exist in this dark zone and certainly none live deeper in the cave. We often see animals in this zone that we also saw in the entrance area of the cave. The twilight zone is usually not long. Turns in the cave passage tend to block penetration of light into the cave.
Bedrock fossils, such as fossil coral, crinoids (sea lilies) and brachiopods (shelled creatures), seen in the walls of our caves were once inhabitants of the oceans that extended through what we now call Missouri. In fact, crinoids are the official Missouri state fossil.
As these animals died and fell to the ocean floor they were covered by accumulated skeletons and shells of smaller organisms and eventually became part of the limestone or dolomite bedrock that is so common in Missouri. The fossils were more resistant to dissolving than the limestone, and we are now able to enjoy viewing them in many caves.
We often see evidence--bones, skulls or tracks--of past use of caves by organisms. Explorers have found skulls of extinct saber-toothed tigers or giant lions in Missouri caves. We might see claw marks or the bed of a bear that hibernated in the cave sometime in the past. As black bear numbers increase in Missouri, we might start seeing evidence of new cave use by bears.
If we look in out-of-the way places that haven't been trampled we might find tiny bat bones. Each species of bat has a distinctive skull, mandibles and teeth. We can identify and carbon-date these microfossils. Such studies can help us understand the severity of past glaciations, the habitat requirements of endangered gray bats, and Indiana bats, and the range of climate changes Missouri could expect in the future.
The majority of the area of most larger caves receives no light whatsoever. Some cave ecologists break this dark zone into two separate zones--dark zone with fluctuating temperature and dark zone with constant temperature. Some organisms seem more likely to live in one region or another.
Probably everyone knows bats love caves. Many bats also roost in forests, barns, homes and church belfries, but some bat species are almost always associated with cave habitats, either roosting singly or in incredibly dense clusters with several hundred bats per square foot of the cluster. Some species live in caves only during the summer, some are found hibernating in caves only during the winter and some live in caves all year.
Bats often roost in the same spots, and their guano accumulates below them. Guano piles of gray bats are sometimes several feet high and several yards in circumference. Regardless of the size of the pile, the guano provides a nutrient source for bacteria and fungi and the small animals that feed on those decomposers.
A student once said ". . . in Missouri, a cave is a hole in the ground filled with mud." Many Missouri caves also contain streams and pools. Salamanders move from the water to the cave floor and cave walls. Another amphibian--the pickerel frog--overwinters in caves.
Other organisms including salamander juveniles, several species of aquatic isopods, small flatworms called planaria, crayfish, aquatic snails, fish and amphipods are restricted to the water.
Because food is so limited in most cave systems, all sources of nutrients are normally taken advantage of by the cave community. In fact, caves that have large bat populations tend to have larger numbers of other animals because the bat guano provides an important nutrient. Caves that often have leaf litter and twigs blowing in through entrances or flushing in through cracks in the cave ceiling also will have higher populations of cave organisms.
The occasional log, guano pile or raccoon scat can be a nutrient-magnet for cave organisms, such as beetles, millipedes, terrestrial isopods and cave salamanders.
Some of the animals we see deeper in the cave look different from those we saw earlier. They are often white or pink and blind. These cave-adapted species have been isolated from the surface environment for many thousands of years. They have lost the ability to produce pigment in their skin or outer layers of the body, as well as the ability to produce eyes.
Cave-adapted species often have other intriguing differences in their biology. Sensory structures (other than eyes) often are more developed than similar species that have never colonized cave habitats. Often their antennae and legs are much longer than their above-ground counterparts and their metabolism seems more adapted to living in a nutrient-poor environment.
Biospeleologists categorize cave organisms into groups based on their use of the cave habitat. Those that would not survive long outside of a cave are called troglobites. Missouri's rich troglobitic fauna include white and blind cavefish, millipedes, crustaceans (crayfish, isopods, and amphipods) and planaria.
Organisms living in caves but not restricted to them are called troglophiles. These organisms also live in forests, basements and other habitats. We consider most species of salamanders (except the grotto salamander) in Missouri to be troglophiles. Other troglophiles include pigmented amphipods, isopods living in cave streams and cave pools, fish that move up streams into caves and many insects.
Organisms that spend considerable time in caves but cannot complete their entire life cycle in a cave habitat are called trogloxenes. They might use a cave to hibernate, as do bears, pickerel frogs and certain moths, or they might roost in caves during the day and exit the cave at night to feed, as do bats and cave crickets.
The category accidental refers to organisms that find their way into caves but are unlikely to survive there. If they do not find their way out of the nutrient poor environment, they will probably perish. Animals that fall down sinkholes (as evidenced by some of the skulls and bones of prehistoric animals) often do not make their way back to the surface.
Cave life is vulnerable to many kinds of problems, such as disturbance or trampling, vandalism, overcollecting, enrichment by sewage and runoff, chemical pollution, pesticides (which have poisoned bats indirectly through their insect prey), siltation or flooding caused by water projects, invading exotic species and urbanization. In the United States, five species of troglobites that we know of have become extinct, four of them in the last 50 years, and 20 species are recognized as endangered or threatened.
Twelve other troglobites are candidates for the U.S. endangered species list, including Missouri's Tumbling Creek cavesnail, Antrobia culveri, known from but one cave in the world. All six species of endangered bats in the U.S. depend on caves at least seasonally.
If we conserve our groundwater properly, much of our Missouri cave life will be protected. We are making progress in conservation by setting aside and protecting bat caves of strategic importance. Of the state's 5,700 caves, only about 155, or 3 percent, are of strategic importance to gray and Indiana bats. The Conservation Department is doing its part by protecting 28 such sites on its lands and cooperatively monitoring the bat populations in other caves held by private, state and federal owners. 
A New Species of Cave Crayfish
Conservation Department biologists Bill Elliott, Ken Lister, Melissa Shiver and Rhonda Rimer collected a species new to science on August 16, 1999. Their work was part of a study, funded by the U.S. Fish & Wildlife Service.
They found an eyeless crayfish in a muddy steam passage in one of the caves at Caney Mountain Conservation Area in Ozark County. Lister collected one adult male and one adult female for identification by an expert taxonomist and Elliott extensively photographed the specimens. Tissue from the female was deep frozen for DNA work by a geneticist, and both specimens were preserved for study.
Elliott was thrilled when he studied his photos of the male's gonopods (mating appendages) and realized that this was a species of the genus Orconectes, instead of one of the two known cave crayfishes in Missouri.
Five species of blind Orconectes inhabit caves from Indiana to Alabama, but this is the first blind Orconectes from west of the Mississippi River.
Finding a new species of cave crayfish is a rare event (the last one in Missouri was in 1952). Some cave species are older than the caves they live in, which may be millions of years old. Some species of cave crayfish have an extremely slow growth rate, low reproductive rate and long life span, so it is important to carefully study and conserve cave crayfish populations.
To protect the new species, access will be restricted to scientific studies. Fortunately, the cave is inside a protected "Natural Area" and is far from any development or known pollution sources.
Photos of many cave species may be seen on Elliott's Biospeleology website at <http://www.utexas.edu/depts/tnhc/.www/biospeleology>
About This Article
Author
William R. (Bill) Elliott has been the cave biologist for the Conservation Department for two years. A native Texan, he has explored and studied many caves in a dozen states, Mexico and Belize. His most exciting trip was rappelling 646 feet into a Mexican pit to a deep lake that contained thousands of blind fish. He enjoys canoeing, hiking and photography in his spare time.
David C. Ashley is a professor of biology at Missouri Western State
College. A parasitologist, he studies prairie fringed orchids and the
moths that feed on them. He also is an accomplished cave biologist and
a member of the National Speleological Society, the Missouri Speleological
Survey and the Missouri Cave and Karst Conservancy. He and his wife, Sharon,
live in St. Joseph and enjoy camping with their three children.
Photos
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Hawk moths (top left) hibernate in caves. Walking fern (top right) prefers shade and often grows in cave entrances. The troglophili spider Meta ovalis (bottom) tends its egg case in its cave nursery.
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The cave webworm is the larva of a fungus gnat. The grotto salamander grows skin over its eyes. Bear claw marks testify to animal use of caves.
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Fungus-coated scat (top left) documents recent use of the cave habitat by a raccoon. Numerous wildlife species enter caves for shelter, food and water.
Evolution has claimed the eyes and pigment of the Ozark cavefish (top right). Other wildlife (from top), including cave crickets, pseudoscorpions, isopods, and cave salamanders, display a variety of adaptations to cave life.
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Cave communities depend on decomposing organic matter. Feeding on bat guano, leaves and dead animals, bacteria fungi (center of illustration) are the first links in low energy food chains, both aquatic and terrestrial. Pink planarian (right)