What is this in the GSP mat?

[kirkland]

We first noticed these weird growths about a month ago. They have been growing quite steadily. We've had the gsp for 8 months now and the mat has spread out. These growths are lighter in color and aren't visible during the day when the polyps are open. It seems strange they didn't show up until recently. Sorry I couldn't get a better picture - my camera is shot and had to use a friend's.

 

[anthony1238]

I'm no expert at all, but looks like what it does when it spreads. just grow out this skin that covers the rock, then you see new ones sprout on it.

 

[paintballer768]

Flat purple mat is just the coral extending its area of growth. My GSP covered under an overhanging rock, and it just had flat mat, possibly because polyps would not have enough light and die.