Yellow web-like covering on rocks?

[Lisasreef]

Hi!

I've started to get what I can best describe as this yellow web-like covering on my rocks. There's little holes in different spots but I haven't noticed any worms, etc, and the yellow stuff is spreading. Has anyone seen this before?! thank you in advance!

 

[Sharkbait19]

Looks like a sponge. Not really harmful unless it’s irritating corals.

 

[homer1475]

Have the same yellow sponge in my tank.

Doesn't seem to bother anything, and will only climb up a coral skeleton, stops just short of the live tissue, and does not irritate the coral.

I've left it alone for years, it grows very slowly for me. Seems to prefer low light, and high flow areas.