I just had a similar problem with an Emerald crab.I purchased one at my LFS in which he was a little larger than the others in the tank. I had heard and read that they were reef safe and friends had quite a few in their tank with no problems. After purchasing a nice large hammer coral and some finger leather coral I noticed within a few days they seemed to be a little shrivelled on one side.I woke up this morning to see the little crab...with the leather in his claw trying to retreat into the rocks for his lunch?...I immediately removed him. Then noticed a few Zoa polyps were gone too...Has anyone else ever experienced this?......I like watching the little scavengers...but eating coral?....I don't know whether it was just a maniac rogue or ? Should I try again?