if it is lobophora. it says emerald crabs,sea hares,turbos,chitons.limpets,tangs and urchins will pick at it.i have a link i copied from here. "nuisance algae id guide". i will post the link when i get to my ipad. really not sure what you have but it looked the closest to pics they had and then i googled it. the cool thing about the link it tells you how you got the algae. and how to fight it. since restarting my tank and getting back into the hobby i come here at least once a day and see whats new.if i can add my 2cents and help.