Two days ago these Zoas closed up and are staying closed.
What could cause that? As you can see from the additional pictures all the rest of my Zoa colony's are doing well.
Just in case, make sure you don’t have any salt creep nearby. It happens all the time, you’re doing something around the tank (shifting a cover, moving a light, feeder, etc), and you inadvertently knock off a small chunk of salt creep and it lands right on a colony. Happened to me with some alien eyes. Colony stayed closed up for a week.