Going off the fine details in that pic, this looks like special live rock compared to norm and specialized growths called periphyton that beards up most surfaces scuba divers will know
real reefs aren’t all open pretty coralline they’re real estate like manhattan, packed with life and that type of growth is often found between corals on large natural reefs
kicked up sand is clinging to these suspects.
haven’t seen the whole reef to see if growths are everywhere
if it’s just that spot, then I’d clean off the growths so sand has nothing to stick to