[lynnvangsnes]

Those are lobophora variegeta. They are indeed brown alge. They will spread and infest all your LR if kept unchecked. I have some in my tank, and I have been fighting for about 6 months. The best way to rid of it is to remove the rock, and scrape the algae off with a wire brush. I got a couple form the hardware store in the form of a welder's brush. Brush off the algae and then use an icepick to dig out the "roots". Rinse with dechlorinated water and put back in tank. To this point, I have not been successful in totally removing them. I am unaware of any natural predators. Just keep after it, and you can keep them manageable.