Algae, sponge or something else??

[samanthabrandon]

I originally thought it was a pretty yellow sponge. I even moved it so I could see it better.I don't have any experience with sponges and don't know if you can tell from the pic. but in the center is yellow and extending outward is a white spongy like substance. The white part resembles a spiders web to the naked eye and seems to be growing at an alarming rate. Its a small rock I just placed it in that spot last Sunday and its already attached it self to the rock beneath it.

 

[Reefing Madness]

Looks like sponge growth to me.