I would tend to agree with Doug, that I would think they would not be picking on an otherwise healthy clam. If though say it's a new clam, maybe it's just a little stressed from the move, and needs to settle in, then of course on top of that being harrassed isn't going to help things much.
If you think the clam looks like it is not liking the extra attention then it may be worthwhile temporarily separating them. I don't know how exactly, putting eggcrate around the clam probably won't work since shrimp are nothing if not persistent and certainly won't let a piece of plastic stop them. Housing them somewhere else (sump? if it's safe that is) or another tank or one of those breeder things.
But, if it looks like the clam doesn't really mind, it could just be that the shrimp is picking at stuff on the shell (mine would sometimes do that to my clams). You could tell the clam didn't mind since it never reacted.
So I guess, watch closely and see how the clam seems to be reacting. If it's well enough as is then I'd leave it be. Intervention, at least I've found, usually only makes things worse for me. I've learnt over time to just "leave it alone" sometimes.
