Steve, I should have mentioned but Swingle didn't think that the BG and LMB were eating the mussels. That's at least in part why the mussel could achieve over 1100 lb/acre standing weight. He thought that the effect of the mussels cleaning the water reduced water quality limiting factors.

Also it isn't just mussels, but any organism that recycles detritus can improve water quality. So things like tilapia, PK shrimp, Asselus aquatiticus, many types of insects, crayfish, scuds, etc. Swingle didn't specifically name these but I think he would include them among organisms that can produce a water quality effect. The mussels are unique in that they probably provided no food for BG and LMB in and of themselves, so it seems very reasonable to hypothesize the effect can be completely credited to improved water quality.

I've posted the link before but knowing you would find it interesting here is the link to Swingle's Biological Means of Increasing Fish Production

It isn't what we don't know that gives us trouble, it's what we know that ain't so - Will Rogers