Can anyone identify this...

[ez2cme]

It appears to be light green and some parts white in color... The stuff is taking over the small rock it's on. I was thinking it might be some type of sponge. And if anyone knows anything about it should I be concerned? It's growing pretty rapidly but it doesn't look like it is going to other rocks as of yet and it hasn't seemed to hurt the mushroom???

Thanks in advance for any help.

 

[paulace2372]

I would also say it was a sponge, I could not identify it beyond that point though.