Swimming Decorator crab

I just looked at the tank (behind me) and this decorator crab is swimming at the surface. No he is not dead. How cool is that?
He can do that because he decorated himself with bubble algae, which is filled with air.
I wonder if he knows thats why he is floating. I had to push him down to grab on to a rock.
I took this from the surface, down

Here he is where he is supposed to be.