Microbes lie as far from charismatic
megafauna such as deer, bears, and bobcats as you can get. Studying
these "forsaken fauna" is difficult because you cannot see them. Their
geologic equivalent is mud, but even with x-ray diffraction and other
high tech methods, the small particle size of muds can challenge the
most dedicated researcher. When combined in caves, however, microbes and
muds can form sediments known as moonmilk.
formations in Oregon Caves
Oregon Department of Transporation photo.
Even the name has the lure of mystery.
Its origin is from the German
Mannlimilch, meaning "little earth-man." European peasants used
moonmilk for centuries to heal infected cuts in livestock. Some believed
that gnomes put this substance in caves for people to use. The white mud
seemed to kill infections and speed healing at supernatural rates. Like
much of what is in folklore, there is more than a germ of truth in these
tales. Much of the calcite moonmilk sampled by investigators contains
actinomycetes, which are the main producers of antibiotics.
Moonmilk is a textural term for a very
fine, white cave material that absorbs a lot of water. Wet moonmilk
looks and feels soft and pasty, somewhat like white cream cheese, when
rubbed between the fingers. Dry moonmilk resembles talcum or chalk
powder, in that it feels hard and crumbly. Moonmilk often contains 40 to
70 percent water, while organic material may make it even more plastic
It is likely that organic activity
plays a role in the buildup of some moonmilk, especially the calcite
kind found in Oregon Caves. Calcite moonmilk can contain such bacteria
as Macromonas bipunctata,
along with cyanobacteria, fungi, and green algae. This microflora
probably assists in breaking down minerals in the wall rock and adding
them to the moonmilk. Moreover, researchers have found that the longer
it takes water to reach the cave, the more likely it is that some of the
organics will be consumed enroute. In general, water dripping into the
deeper parts of Oregon Caves has less organic content than water
reaching shallower parts.
Humans have impacted bacteria in
moonmilk, as well as other microbe populations in Oregon Caves. An
inventory done around every survey point in the cave shows a marked
decrease in "cave slime" (mostly
actinomycetes bacteria) growing on walls near the cave trail.
Decline in these organisms could well be the result of lint and other
visitor-induced organics that find their way to cave walls. As a result,
non-native bacteria adapted to a high energy food source outgrow and
outcompete the slow growing cave slime adapted to low energy foods. Cave
slime may also have suffered further adverse effects by visitors
touching the cave walls, or through the past practice of spraying those
walls with bleach to control exotic plants.
As an example of their value to
resource management in the park, microbes have been utilized to
reconstruct the size and shape of prehistoric entrances at Oregon Caves.
Since the natural openings are now highly modified, an inventory of the
directional orientation of popcorn-shaped speleothems was needed so that
gates could be built with partial restoration of those conditions
resembling prehistoric air flow. The cave inventory also showed that
exotic microbes contributing to rounded vermiculations (or "clay worms")
are more common near the main trail, while the more complex forms of
these lines on cave walls are prevalent further from the trail. Analysis
if the rounded vermiculations show high amounts of lint and exotic
cyanobacteria. The rounded clay worms will be removed, as they appear to
be largely caused by lint and artificial lights.
Deposition of lint, skin, and hair in
Oregon Caves does not appear to impact native microbes as much as in
some other caves administered by the National Park Service. Knowing this
has allowed flexibility in the design of a new cave trail. Rather than
having settling "ponds" and a foot-high, lint-trapping curb on both
sides of the trail along its entire length, only certain areas will be
curbed or have drainage concentrated. If these areas trap substantial
lint and non-native organic runoff, then additional curbs, drains, and
settling ponds will be added and the areas cleaned more frequently. This
system will allow for a more natural flow of water and air across the
trail, yet will trap lint and other human-associated organics where they
might threaten cave biota. The result should be a better balance between
allowing for visitor use and preservation of the monument's primary
John Roth is the natural
resources management specialist for Oregon Caves National Monument.