Do you have an urchin, clown goby, or emerald crabs?
Just to make sure I'm seeing what you're seeing - does it look like tissue is missing? Any sort of bite marks near the coral (like on rocks) or anything?
None of the above creatures. No visible bite marks anywhere else, or any other coral. Because of the location, I did wonder if one of my tangs was not paying attention to where he was biting when he was nibbling on the rock work.
Yes the tissue was missing in that circular pattern, and was apparently tissue in the center. I did scrap at it to be sure it wasn't anything still on the coral.
Below this Pearlberry, is a favia or favites coral. It can get a good set of sweeper tentacles at night, but I've never seen them get close to the Pearlberry.