What is this?

[JEFFRO33]

I have been noticing these weird looking yellow growths on my live rock.Can someone tell me what it is and if it is bad.

[niftyjosh]

looks like sponge

[Broog]

looks like sponge

+1

[Kamel]

+2, was even thinking that before clicking the pic to make it bigger

[Baley]

+3 I have them all over one rock. I was told that is what it is by someone who has been running saltwater tanks for 10+ years. He said they were just fine and no problems.

[reefer4ever]

its a sponge. it acts as a natural filter and is very good for your reef. i have tons of sponges of various kinds.