LONG TERM CHANGES IN A SHALLOW CHANNEL BORDER MUSSEL COMMUNITY
OF POOL 19, MISSISSIPPI RIVER.

Richard V. Anderson.  
Department of Biological Sciences, Western Illinois University, Macomb, IL 61455.

In order to track changes in native mussel populations, the mussel community found in the
shallow channel border area of Pool 19, Mississippi River has been quantitatively sampled from
1983 to present.  The site most frequently sampled is located adjacent to Devils Island at
RM378.5.  During this 17 year period the mussel populations have been subjected to infestations
of the Asiatic clam and zebra mussels and river level changes as a result of drought and flooding. 
Mussels were quantitatively sampled by hand searching between 20 and 100, 1 m2 quadrants in
June or July.  Mussels collected were identified, measured, examined for epizoon and returned to
the river.  Using either Simpson's or Shannon's diversity, there has been a general trend toward a
slight decrease in diversity at the site.  Neither the presence of the Asiatic clam nor the 1988-89
drought appeared to effect species composition or density.  Following the 1993 flood, 3 mussel
species which had not previously been collected at the site were found; paper pond shell, white
heel-splitter, and lilliput.  The paper pond shell was abundant following the flood and all 3
species continue to be present at the site.  Zebra mussels were first collected from native mussels
at the sample location in 1994.  Since that time, zebra mussel infestation frequency and density
has steadily increased.  In the past 4 years, infestation frequency has exceeded 80% and the
infestation density has reached 35 zebra mussels per native mussel.  Since 1994 mussel density
has significantly declined.  In particularly, densities of deer-toe, fawns foot and three-horn have
been greatly reduced at the site.  Zebra mussel infestation appears to have had a greater impact on
the native mussel community than Asiatic clams, severe drought, or severe flooding.

Keywords:  native mussels, disturbance, channel border habitat, Pool 19, Mississippi River