Tunicates and Sponge are awesome. We want these animals to grow in our tanks. They filter the water. The growth of these is what makes a tank more mature and stable. These are some of the Benthic organisms that make the ocean so diverse with life.
Not only will it grow on the underside of LR, but Sponge will grow between rocks, holding them together, making the aquascaping more stable.
Sponge comes in many colors - black, white, blue, pink, purple, green, etc. Sponge usually grows in darker areas. A piece of LR that is repositioned which then exposes the colorful Sponge may seem to lose that sponge over time. Not to worry, usually this induces the sponge to spread to many other dark places in the tank.
I gather sponge from other hobbyists. Until I sold it all, I used to grow and share pieces of Blue Barrel Sponge that grew from a small cutting freely give by another hobbyist(thanks Tileman). Currently, I have some yellow-green sponge which grows in the light and looks so
good that, like coral, I frag it, attach it to rock and spread it
around to other tanks.
Fragging Sponge is easy. Pull it apart with fingers and use an elastic to hold it to a small rock. When it has grown to the rock and around the elastic, simply snip the elastic with scissors, then pull the snipped elastic through and out.
Aloha,
Mark
"color changing" Sponge grows dark green or black in lighted areas and white in shaded areas.
Pineapple Sponge is common in many reef aquariums