Hi,
I found my first peppermint ate mushrooms and zoanthids, my current 2 in the reef are good so far but I do feed shortly before lights out and they grab whatever the fish miss. It was when I changed to feeding in the morning that the elder shrimp started attacking my desirable fauna.
They can be trained to recognize the feeder/apparatus so if you figure out where they spend their days you can take a long tube, tweezers or pipette and hand them food right before dark to keep them satiated. They learn this trick in about one day if they like what you feed.
I placed my yellow polyps and mushrooms away from their favorite hangouts out in the open where they will feel less safe and have cardinals which patrol at night, this probably makes them nervous. They don't bother the critters on top of the rock they live under so apparently so far so good. Catching a rogue peppermint is not easy either! I think they are great in refugiums where you can place aiptasia infested rocks for them, and they will spawn sending food into the main tank.
I have watched an emerald crab eating acro, tried to get a picture but it was out of focus. The crab was under it and reached up to scrape off the edges of the coral's base. Probably doesn't hurt too much but concerns me a bit. Perhaps our confidence in specialized crustaceans is not warranted... they don't do what we sell them to do! Don't they read the internet? Emerald crabs are valonia eaters! Right... Not one of mine has any desire to touch my bubble algae infestation...
Kate