What’s this black stuff on live rock near coral?

[CmMagenta]

I recently bought a live rock from a store that had a few soft corals on it. I have no idea what this black stuff is but I’d like to understand/identify it. Does anyone know what I’m looking at here?

 

[jeffchapok]

Sponge is my guess.

 

[Hincapiej4]

Yes. Sponge

 

[CmMagenta]

Yes. Sponge

Will it kill the coral on the rock?

 

[Billdogg]

Yes sponge, and yes it could kill the closer corals by encrusting over them. If it becomes an issue just trim it back. Over time you will also have yellow, red, pink, white, green, and occasionally, blue. IME, they are almost always harmless and a sign of good water quality.

 

[DrZoidburg]

Yep black sponge I agree. That one can be pretty invasive.