ID of bright yellow encrusting "something"???

[pegasus]

I think I've asked for help on this one before, but I can't seem to locate it, so here I am again. This is a very bright yellow, encrusting, rough, calcareous growth. I have a single rock that has a lot of this covering it, and for the longest time, I thought it was dead. After two years, it is slowly starting to spread. It has covered the base (roots/mat) of the Anthelia growing on the rock. It has even formed a small stalagmite that has attached to the rock above the one it's on. I took the picture at night when the Anthelia was sleeping. There are small patches of yellow sponge growing in spots on and around this "something", which can be identified by it's darker, greener color. I'm not concerned about any danger from this mystery creature... I'd just love to know what it is.

 

[bang guy]

Looks like some type of sponge.

 

[pegasus]

Thanks for the reply, bang guy. At first glance, it has a similar appearance as the yellow ball sponge growing around it... however, it has a very rough texture to it, like really coarse sandpaper. It lacks the open membrane like the ball sponge, and it's as hard as rock.

There's a small patch of yellow ball sponge in the center of the first picture, and to the right/center in the second picture. They appear to be part of the larger growth, but I assure you... they are completely separate/different. There's a small patch of purple sponge in the upper half of the third picture. I have numerous growths of these sponges, with some growing larger than baseballs. They always remain soft and flexible. I know there are several other varieties of sponges, but I'm not familiar with any that resemble what I have.