What causes skirts to curl down?

[PiscesPower]

I’ve had these WWC Gaias for a few months. Added the same time as the others in the photo. What causes the skirts to curl down? They are at the bottom of the tank but I have many others that low. They are growing as it started as 2 polyps in July.

 

[reeflife3]

I have some that do the same thing, I don't think anyone knows exactly why it happens

 

[Lovemyreef2015]

I noticed when I had a alk swing ours did that. Not sure if it was related though.