Most puffers eat inverts and it would not supprise me if the sharp nose puffer ate them to. He or she might even eat corals.Depending on what you have in your reef.
I agree. The puffer would most likely decimate your crustacean and mollusk populations, and then your pods and detrivores. You would most likely see it blowing the sand and eating whatever happened to get uncovered. I don't think it would touch your corals, though, but maybe a few softy polyps.