ZEBRA MUSSEL (DREISSENA POLYMORPHA) COLONIZATION IN POOL 8
OF THE UPPER MISSISSIPPI RIVER AND EFFECTS OF PREDATOR
EXCLUSION CAGES

Michelle R. Bartsch, Lynn A. Bartsch, Steve J. Gutreuter
U.S. Geological Survey , Upper Mississippi Science Center, La Crosse, WI 54602
 
During 1997, we assessed the effects of predator exclusion cages on zebra mussels
demographics in Navigation Pool 8 of the Upper Mississippi River.  Concrete
blocks were deployed from May 22 to October 29, 1997, at two sites, in two
habitat types (main channel border and backwater) of the Upper Mississippi
River.  At each site, two blocks were deployed, one of which was enclosed in a
cage (60 cm long X 31 cm wide X 31 cm high, mesh size 7.3 cm X 5.0 cm); the
other block was uncaged.   At the end of the 159-day colonization period, zebra
mussels were found at both sites.  Densities (number/m2 ) and biomass (g dry
wt/m2) of zebra mussels were higher on caged blocks than uncaged blocks.  Mean
mussel biomass on uncaged blocks was reduced by 81% relative to caged blocks
across both sites and habitat types in Pool 8.  In addition, mussel length-frequency
distributions differed between caged and uncaged blocks at both sites. 
Interestingly, the more sheltered surfaces (i.e., holes) of uncaged blocks had
substantially higher densities of mussels than the exposed surfaces (i.e., top and
sides).  The mean total length was greater for mussels found in holes (13.1 mm) of
uncaged blocks than exposed surfaces (5.7 mm, top and sides).  However, on
caged blocks no differences in mean length of mussels occurred between holes
(15.6 mm) and exposed surfaces (16.0 mm).  Our preliminary results suggest that
predation may have an effect on zebra mussel demographics in Navigation Pool 8
of the Upper Mississippi River based on artificial substrate samplers deployed in
sentinel sampling sites.

Keywords: zebra mussel, predation, Dreissena polymorpha, Upper Mississippi
River


Michelle R. Bartsch
Upper Mississippi River Science Center
2630 Fanta Reed Road, La Crosse, WI, 54602
Phone:  608-781-6285
FAX:   608-783-6066
Email:   Michelle_Bartsch@usgs.gov

Poster presentation

Author not a student