Nope. Not Acropora sp. Not Montipora sp. Not Anacropora sp.
This is Eucheuma arnoldii … a red ALGAE that mimics Acropora. Wild, huh?! Photos A and B are of E.arnoldii, and photo C is Acropora vaughani, which grows in close proximity to the algae on the Great Barrier Reef. E.arnoldii exhibits tapered branches with light colored tips that mimic an Acropora’s growing axial corallites. The fake radial corallites and arborescent growth form are a spitting image of staghorn corals. This is Batesian mimicry at its finest. This algae has found one great way to avoid being eaten by tangs.