Had to share this with everyone. It's an old paper, and I'm no professional ecologist, but Mackie, et. al. 1989 has this to say:
"Crayfish could have a significant impact on the densities of 1 to 5 mm long zebra mussels. An adult crayfish consumes an average of nearly 105 zebra mussels every day, or about 6000 mussels in a season."