Nassarius do a fair job at stirring the sand, small and hardy as well. Fun to watch too, they do flips! I've heard ceriths also stir the sandbed. From what I've read, stirring the sand helps to clear detritus from building up in inaccessible areas, it also prevents air pockets from forming which can lead to sulfur dioxide build up. I think I got that right, might want to double check about the benefits of sand stirring.