Pretty sure inverts will gobble on it such as urchins and starfish , dunno how much rock it?s actually covering but I just used a toothbrush to scrub it all away and have a small powerhead to suck up the little bits
hmm not 100% positive. if in doubt, take it out. could it possibly release spores of some kind, cells that can reproduce elsewhere? someone else might know better, but it sounds plausible since sponges can be asexual and sexual species.