I have what looks to be the exact same stuff. I'm no longer convinced that it is actually Botryocladia but if it isn't, it's a close relative. I have a couple algae books that list about 5 genera that look pretty much just like that. Those dark red / orange spots are reproductive structures and I think you have to look at how those are put together to ID it even to Genus. Anyhow, it isn't "bad." It grows slowly and is easily manually removed. I imagine most sea urchins would love to eat it, too.