acros sometimes have little crab guests, and if the acro looks good now, leave the crab there. The crab has probably been there for a while. It will survive on bits and pieces that float into the acro's branches and will keep it clean.
I agree with carpenter. Some say the hairy legged crabs are a problem but I 've never had any problems with these crabs in coral heads. They seem to have a mutually beneficial relationship......
