My leathers (the one's down at the bottom of the tank) always do this. Usually when the sand/substrate is moved away from their base. Never had any problems, just not very pretty.
The other just looks like hair algae or bacteria. You will have to scrape it off to get rid of it, but it will come back unless you determine the cause (such as over feeding, excess poop, skimmer not taking out all the bad stuff, etc).
Love the cave in the rockwork...very nice