No idea.

But I do have a couple spots of "sponge" (presumably!) that are more slick and rubbery and it is very hostile to corals, will grow over them and smother and kill them. Sponge is typically more porous, delicate, fibrous, and, well, spongey for lack of a better description! I have it in a couple different colors - not yellow - and in two different tanks. Wonder if this is the same stuff? Can you get a picture of yours? I could maybe try to get a pic later but I've tried to peel away most of it now that I realize how un-friendly it is to coral.