Selective feeding by three native North American freshwater mussels implies food competition with zebra mussels

We examined the ability of three species of native North American freshwater mussels ( Margaritifera margaritifera, Amblema plicata, and Pyganodon cataracta) to preferentially ingest or reject various phytoplankton species and nonliving particles. Our objective was to: ( 1) determine the particle preferences of the native mussels, ( 2) determine whether native mussels are able to differentiate between nutritious and less nutritious particles, and ( 3) compare sorting abilities and particle preferences to those of the invasive zebra mussel ( Dreissena polymorpha). Native mussels selected and preferentially ingested the unicellular cyanobacteria Microcystis over most other phytoplankton species. However, despite their ability to select between phytoplankton, they did not select against cattail (Typha) detritus. Our results suggest that native mussels ( 1) prefer particles ( Microcystis) that may no longer be abundant in some systems, such as the Hudson River, ( 2) must compete with zebra mussels for the same preferred food types ( Microcystis), and ( 3) are unable to differentiate between nutritious ( phytoplankton) and less nutritious ( Typha detritus) particles. We suggest that native mussels must compete with zebra mussels for many of the same food types and are less efficient than zebra mussels at differentiating between nutritious and less nutritious particles. This indicates that there is an additional mechanism, other than direct physical interference, contributing to native mussel mortalities following zebra mussel invasions.