I believe that is neomeris annulata, the worst invader of them all really. id choose a bad species dino infestation over two of those rascals on my rock.
that just means remove the rocks they are on and deal with it outside of the tank. for sure as with any invader there are examples of it staying controlled, however try to find an example of an invasion being cured and ill link it to giant peroxide threads where people went insane with the stuff and it fended off everything we threw at it including 35% and rasping of rock surfaces to the point of metal gouging and it still grew back massive takeover.
This invader has nothing to do with nutrients as causative or cure, its strictly the hitchhiker that wears the hockey mask and we still pick it up anyway.
*marine algae database, the grail of our IDs, lists them as moderately easy to keep heh. six years ago a poster named NACL we can still read about in the giant reef central perx thread dumped gallons of 35% into his reef to purposefully nuke everything, cause a terrible recycle, and it still came back lol
poster WindyRidge in the reefcentral peroxide thread used a flatblade screwdriver and ice picked it out of her rocks and actually won that round and seemed to beat it. the stuff is inconsistently insane.