I can't think of the name right now--it's typically not as invasive as caulerpa, but will require occassional thinning. Good stuff--we've been trying to find some for a while now!
i've been doing a little research and I'm not possitive, but I think it is Red Turf Algae. I haven't been able to figure out how to get rid of it, or atleast cut it down a little.