Can't tell what this is...

[Mat1018]

If anyone know what the purple redish looking barnical like things are and the little star like trees growing out of them.

 

[Khemul]

The rock itself looks like it was once a Pipe Organ (Tubipora musica). The polyps could be remnants of the colony or they could be one of the similar looking corals. It'll depend what they retract into. If they retract into structures like what makes up the rock, Pipe Organ polyps. If not, maybe Clove Polyps or similar.

 

[Mat1018]

So will they spread over time and repopulate the rock?

 

[Khemul]

Yep. They did it before, they'll do it again.