A Study of Freshwater Ostracods from Pop's Cave, Mill Creek and a Spring in Richland County Wisconsin.

 The author studied the relationships between several species of freshwater ostracods living in three different environments, a cave, spring, and creek.  The following paper shows the diversity of the ostracods in each area.

Introduction
 In February 1992 a small sample of sediment was taken from a spring near Pop's cave.  After a few hours it was noticed that many small ostracods were crawling along the bottom of the aquarium.  An ostracod is a small almost microscopic shrimp that lives in a bean shaped shell or carapace.  They live in both salt and freshwater and can be found world wide in oceans to mud puddles.   After reading articles the author found that not much was said about ostracods in caves.  It was then the author decided to check Pop's cave, that is located a little less than half a mile from the spring, and the creek to see if these too contained ostracods.

Study Area
 Richland County is located in the southwestern part of Wisconsin and is known for its many springs and caves.  Sabin Township is situated in the northwest corner of Richland County.
 Popp's cave is a well-known cave that is located 110 feet above the West Branch of Mill Creek.  It is in the Prairie Du Chine Dolomite and contains 640 feet of passages.  Average temperature in the cave is 56 degrees Fahrenheit; the water temperature averages 45 degrees Fahrenheit.  A water chemistry test was done in the cave by the author in 1993 and again in 1997.  The oxygen content, in 1993 was 11 parts per million and 1.2 mg/L in 1997.  The water pH was found to be neutral both times.
The cave receives runoff that comes in from the entrance during rain storms or snowmelt.  The back of the cave has a higher elevation and receives most of its water from seepage.  This may not account for the presence of ostracods.  Samples in the cave were taken from large puddles of water marked on figure 2.

 The spring comes out of a neighboring hillside and runs into the west branch of Mill Creek.  The spring is about 50 feet long and 15 feet wide at it's widest.  The water chemistry was taken in 1997 with an oxygen content of 8.1 mg/L and a neutral pH. The temperature was 48 degrees Fahrenheit.  Since the spring never freezes there is still enough green plants and organic material to supply the living organisms year round.
 The creek begins at a small spring located about a half mile to the west.  It is fed by numerous other springs and runoff before reaching to the collection site.  The collection site was located under the old bridge on Town Line road and about 10 feet away from the spring mouth. The temperature for the creek was 54 degrees in the summer of 1993 but the collection site had ice over it in the winter.  Vegetation was sparse; however an organic film was present.

Methods
 Two batches of samples were taken at two different times of the year, the first in February and the second in June of 1993.  One sample was taken at both the spring and creek where as seven samples were taken from the cave.  Each sample was placed in a small jar, trying to get as much sediment as possible.  Samples from the cave had less sediment than the spring or creek due to low amounts of sediment and access problems.
In the lab one to two tablespoons were rinsed through a screen.  The samples taken in February were rinsed through a 250 mesh screen while the samples taken in June were washed through a 100 mesh screen. A blue dye was added in June to check for living ostracods.  This process shows the live ostracods by turning them a blue color as they ingest the dye.   No live ostracods where seen in the cave samples using this process but where present in the spring samples.
 After screening, each sample was placed in and drying oven and then hand picked using a binocular microscope.  Each sample was placed in separate microfossil slides for storage and later examination based on locality.

Results
 The cave was one of the hardest sites to sample.  Samples were taken from seven different locations in the cave.  Samples, from the largest pools in the cave, yielded the highest number of ostracods per tablespoon of dried material.   Samples taken from some of the smaller pools yielded fewer organisms and only one pool yielded none. The list of the three species found is as follows:  1  Candona lactea,  2.  Candona crogmaniana  (female),  3.  Candona crogmaniana (male) and 4.  Cypridopsis sp.
 
 

 How the ostracods got into the cave is a mystery.  Most likely they were carried to the cave by bats or raccoons, which in turn picked them up while drinking from the creek. Another method could be that they were carried in and left in raccoon feces.  Studies have shown that an ostracod can survive up to several days in a ducks stomach (Scharf 1977).  This may explain the large amount of fish and frog bones found in some of the sample areas.  A final and less likely way was that they were carried in on the shoes and clothes of some of the hundreds of human visitors each year who may have picked them up while crossing the creek.  The cave had the second largest abundance of ostracods seen.  The cave shares only 2 species that are found in the creek and spring.  Candona lactea and Candona crogmaniana.

 The spring was the only sample locality that produced live ostracods.  They were observed under low power magnification feeding on organic debris coating sand grains.  The specimens taken in February lived for 4 months.  Samples taken in June also contained live specimens.
 Under magnification the internal organs could be seen.   Eyes could be seen clearly.  Due to pigment in the eyes it can be said that these animals have the capabilities of seeing light and dark.  No reactions were noted in lab studies however. The spring turned out to have the greatest abundance of ostracods, however only 2 species were present.
The following species were collected from the spring. :1. Candona actula, 2. Candona lactea, 3.  An ostracod egg, (fig. 1) a slight bit smaller than the three to the right (3 ), and 4.  A male Candona lactea with  Zenker’s organ exposed (fig. 2). The Zenker’s organ is part of the reproductive system in ostracods.

Fig. 1
 

Fig. 2

 The samples taken from the creek introduced new species that were absent from the spring and cave.  The creek sample produced the following species. 1.  Candona albicans,  2.  Candona species,  3.  Candona crogmaniana,  4.  Candona crogmaniana (young).  No live specimens were seen however a few live micro clams were present in the samples.  The creek had the third largest amount of ostracods.

 The presence of these small ostracods is a field that needs more study.  While they are noted as being present in caves very little has been written about them.  Hopefully this paper will bring a better understanding of these small creatures.
 
 
 

References
Monre, Raymond C. et al  1969.   Treatise of Invertebrate Paleontology.  Part R Arthopoda 4, University of Kansas,  pp.Q13.

Scharf, Burkhard W.  1977.  Living Ostracods from the nature Reserve “Hordter Rheinaue”  (Germany),  17 pp.  Kettelerstr, Mainz Germany.

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