the part of Santee-Cooper lake in SC that produced the world-record shellcracker had had a recent influx of Zebra mussels shortly before the record. They could possibly be okay if you had a good number of shellcracker in the pond; oftentimes they'll find their way to a pond without help, much in the way frogs do.
I could be wrong but I believe the species of bivalve that invaded the Santee Cooper that assisted the shellcracker along was the Asiatic clam.
http://www.dnr.sc.gov/water/envaff/aquatic/zebra.html It too is quite invasive but in a different way. I recently introduced them into a pond as a test to see how they do in a small pond environment.
See
http://www.pondboss.com/forums/ubbthreads.php?ubb=showflat&Number=158752 for further info on the Asiatic clam.
