I once brought some macroalgae back from Costa Rica. It looked just like that (and other pictures of Dictyota that I've seen), so I can only assume it was Dictyota. I put it in my tank hoping it would grow. I noticed my queen conch nibbling on it that night. The next day it was gone. I was so mad at that conch, but maybe it was a blessing in disguise now that I hear what a pain this stuff is.
Of course this could have just been a fluke as well. Something to consider anyways.
-Chris