Part of the reason I got my melanurus was to "protect" my SPS. (Plus, they are very pretty and personable, IMO.)
So, today I got a new acro colony and while I was giving it its dip, I noticed a decent sized acro crab nestled in it. The dip did not dislodge it, and I wasn't sure if it was alive or dead, and I didn't want to risk hurting the acro trying to get it out, so I thought I'd just put it in the tank and see what happened.
The melanurus (nicknamed "fatty" cause he never misses a meal) watched me place the coral and sat hovering inches from it while I got it into place. No sooner was I out of the water, when he went after that crab. He deftly pulled it out of the acro, dropped it once to get a better hold, then grabbed it again and repeatedly smashed it against a rock until it broke into many pieces. He quickly gobbled up all the bits and even had part of its shell in its mouth and swam around the tank seeming to proclaim, "I AM KING OF THE CRABS!"
Was entertaining...I love that fish.