I think a lot of people have the wrong impression about these particular crabs. I've have had them for a long time and they don't seem to do any harm to the acros. The black clawed "Teddy Bear" crabs can have strong pinchers and are capable in snapping some thin branch acos. I have always liked to keem them b/c they get rid of most acro pest. They seem to mainly only pick the decaying tissue on the acro, allowing the new tissue to replace the old tissue. Sometimes, this can seem to increase the mitosis rate and stimulate new growth.
Here is my theory...Acro crabs only arrive in acropora colonies picked from the ocean, wild or maricultured. These are incredibly more sensitive than aquacutlured acros and are likely to suddenly start to RTN or bleach. I just really think that these crabs are the first ones to get blamed when an acro colony dies when in actuality, there are a number of causes of death.
If you put them in the sump, it is very likely that they will not make it due to a lack of food source. When the acro dies, so does the crab.
