im just wondering... what type of trigger is it? it almost looks like a tassel filefish to me, but that jsut might be the quality of the picture.
triggers are agressive preditory fish. A Niger is the only type that i have seen in a reef set up. They will eat many other types of fish smaller than themselves as well as crabs, snails, shrimps, and hermits. Also they have been known to pick at corals. I think it is highly unlikely.
what size tank is it?