The problem with the whole "PC & Mac Discussion" title for this forums (which is stupid, because Macs are PC's in every reasonable interpretation of the term at this point) is that it is really a Windows forum.
It would be better to check the steam forums for the game. I wasn't able to find a solution after a brief check, but that will be where you'll find one if the developers do have a fix to your issue.
I have far more game problems running Mac OSX, then I do running Windows. "Mac's don't crash" my ass.