I have no idea what this is

[Nate_]

Hey all in internet land, I was wondering if you all could help me with an ID of whats growing on my rock!

here is the picture from my iphone:
http://a3.sphotos.ak.fbcdn.net/hphotos-ak-snc6/253516_10150216832579675_515184674_6900569_4070165 _n.jpg

Any help would be greatly appreciated.

Thanks Nathan

[mark]

sponge (good)

[Nate_]

Thanks wasnt sure because I have never seen a sponge like that before.