Diodogorgia nodulifera polyps extension mystery

I didn't know where to put this thread maybe the mod can help me here thank.





I have a Diodogorgia nodulifera









The red dots are where the white polyps retracts . When the branch is not healthy they disapear and the branch waste away.









here you see a few guards polyps on duty , that measure particule concentration, if present they'll entend and soon the others will entend.







That in theory goes with strong flows; However!!!!