My friend, You should know about me one thing...I do not take out crabs, due to the reason I strongly belieave that if the crab is being fed it is not going to attack anything else.... The only thing i have removed from my aquarium are the FIng bristle worms :)
Xanthid coral crabs form symbiotic relationships with coral. They live in and feed on the coral in return for defending it from more voracious predators such as crown-of-thorns starfish. Although the crab itself eats some of the coral's polyps, there is no evidence to suggest that the coral is harmed by this low-key feeding. In fact, corals with crabs associated are generally more healthy than those without, probably because they do not suffer large-scale attacks by more voracious predators.