At one time they got so bad in the Mississippi they covered nearly everything.When the water would be up for a while then drop it was amazing how much stuff was covered with them. I thought they were going to destroy the river before the Asian carp ever came along. But lo and behold I started noticing them in some catfish bellies and it seems like they have tapered off some now.So I guess the catfish decided to eat some of them,then again the catfish have always ate mussels and these things drove out some native species.
Really best to not transfer anything from place to place....lot of different parasites and stuff that do not need a ride.