I would pull the rock out and break off the plating coralline. I'm not sure the coralline is making them all close up like that though. From the picture, you can see that even the polyps furthest away from the algae are closed up as well.
Try taking the rock out and carefully cleaning it off.
The plating coralline can be quite beautiful though. Here you can see a tiny frag of blasto merletti i got years ago and the little piece of coralline in the center-
and here's what it became-