Strange pest house

[dmsc2fs]

I have this strange AIRBNB showing up. I see 4 of them. It’s a strange pod like bubble and it appears to be growing out of the base of a few coral. Any clues?

 

[ISpeakForTheSeas]

Any chance you could get a clearer photo? I can see the coral relatively well, but not much else. That said, here are some things that - based on what I can see - could potentially be your hitchhiker: Tunicates, new coral heads, barnacles, and sponges.

Tunicates would be my first guess from what I can see.