Shaving Brush (Penicillus sp.) are highly calcerous, much like Halimeda sp. of macroalgae.
Most tangs do not eat halimeda, presumeably due to the taste and texture. I am not discrediting USINKIT, but I would be tempted to disagree.
Here comes "Mr. More Than You Need To Know Man"...
Shaving brush has a life cycle of 30-35 days. It will appear as though it is dying, by bleaching out and disintegrating, but are actually multiplying. They will grow very similarly to fungi vs. a typical plant. The Penicillus will shed its "limbs" and those will re-appear in concentric rings a week or two as a whole new colony.
Don't ask how I remembered something like that, but can't find my car in a parking lot.: