A numerical model for simulation of freshwater mussel dynamics was used to investigate the effects of substrate and hydrodynamic conditions on the formation of mussel beds in a 10-km reach of the Upper Mississippi River (UMR). Suitable habitats for mussel survival were identified by creating a dimensionless parameter (shear stress ratio) combining shear force and substrate type. This parameter is a measure of substrate stability that could be used in many different applications. Dispersal of juvenile mussels with flow as they detach from their fish hosts was simulated by a particle-tracking mechanism that identified suitable areas for colonization with the potential to evolve into mussel beds. Simulated areas of mussel accumulation coincided with reported locations of mussel beds, and simulated densities were in the range of abundant mussel beds in other reaches of the UMR. These results, although more qualitative than quantitative, provide insight into factors influencing the formation of mussel beds in a large river.

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, 2003). Most methods are built on a more or less complex physical element that uses hydrological or hydraulic data that have, or are assumed to have, biological significance. Some methods benchmark regulated rivers against natural ones using paired rivers or reaches, or historical (pre-impact) data series. Other methods depend upon empirical data on the range of preferred to unsuitable habitat conditions for a target species, or life stage, and assume that spatially derived habitat suitability curves are transferable to predict biotic responses to flow changes over time. Rapid growth in the use of these physically based models has been important in addressing an array of immediate river flow management issues, but increasing concerns about limits to available water

The dispersion of invasive species is a serious problem worldwide. In North America in particular, the introduction of the zebra mussel (Dreissena polymorpha) has caused millions of dollars in economic losses and environmental damage. This paper uses ecohydraulics modeling to analyze the effects of zebra mussels on native freshwater mussel communities (unionids) in the Upper Mississippi River (UMR), USA. The model takes into account environmental forcing functions and individual mussel interactions in the form of food competition. First, hydrodynamic transport of incoming zebra mussel larvae was simulated to assess their colonization patterns on unionids. Next, population growth at various food availabilities was computed. Simulated zebra mussel densities were within the range observed in published studies and survival rates of unionids coincided with reported values for an upstream reach of the UMR. These results suggest that these two families of species may coexiste in the UMR, although the sharp decline in the unionid populations may eventually result in extirpation due to unsuccessful egg fertilization. This model provides the means for better understanding the interaction between native and invasive freshwater mussel species and it may be a valuable tool supporting the development of appropriate conservation strategies for unionids.