Comparison of Native Mussel Assemblages Among Three Reaches of the Upper Mississippi River

Science Center Objects

In the past century about 20 mussel species have become extinct from the Upper Mississippi River (UMR) basin, and at least 28 species are state or federally listed.  The species composition appears to have changed considerably from pre-European settlement times toward communities dominated by mussels that are tolerant of pollution and can utilize many different types of habitats.  River managers lack scientific information to confirm these observations.  For this study, scientists evaluated patterns in species composition from systematic surveys of mussels that were conducted in three reaches (Navigation Pools 5, 6, and 18) of the UMR during 2005-2007.

Impact of UMESC Science

These apparent changes in diversity and community structure are probably driven in large part by human alteration to the system because the overall mussel distribution is strongly tied to hydrophysical (i.e., water flow and hydraulic conditions near the river bottom) and upstream-downstream fish population patterns in the UMR.
 

The results of this study suggest that river management goals and actions in the UMR may need to account for important differences in mussel communities that occur among reaches. 

How do the mussel communities compare between different areas of the River?

  • Pools 5 and 6 have very similar community structure to each other, but Pool 18 has a very different community.
     
  • Species richness and species density was higher in Pool 18 compared to Pools 5 and 6. 
     
  • Across all three reaches, four species dominated recent mussel surveys, including threeridge (Amblema plicata), threehorn wartyback (Obliquaria reflexa), pimpleback (Quadrula pustulosa), and mapleleaf (Quadrula quadrula).
     
  • The mussel community in Pool 18 contained higher abundances of three Quadrula species (Q. quadrula, mapleleaf; Q. pustulosa, pimpleback; and Q. nodulata, wartyback) and lower abundances of threeridge (A. plicata) and Wabash pigtoe (Fusconaia flava) compared to Pools 5 and 6.
     
  • Longitudinal patterns in the species composition of native mussels might be partly explained by patterns in the distribution of fishes that are used as hosts for mussel larvae.  For example, higher abundances of catfishes in Pool 18 could affect relative abundance of mussel species including the three dominant Quadrula species in Pool 18, because they strongly depend on catfish hosts for their larvae.
Number of Freshwater Mussel Species in the Upper Mississippi River System

Number of Freshwater Mussel Species in the Upper Mississippi River System Pools 5, 6, 18, 1920-2006/2007(Public domain.)

Have the mussel communities changed over time?

  • The UMR appears to support a large fraction of its historic number of species, however species composition has substantially changed over the past 150 years.
     
  • Recent data detected 16-23 species in these 3 reaches, compared to 28 species detected in a 1920 survey (although note that sampling methods were different, which can bias these results).