Also, you should be able to reduce your power consumption a bit by changing CKOPT=1; read the description in the datasheet (you may not want to if you're in a noisy environment).
I'm gonna do my best here to not go off on a rant.
CKOPT should NEVER be left at 1 unless you're using a crystal specifically selected for low power operation. This will be something with a low loading cap spec like 12pF or thereabouts, and you'll be well advised to do oscillator margin tests.
As yet, I have not seen any guidance from atmel on selecting crystals for this mode. When I asked them about it directly they asked that I forward any information on any good candidates to them, which does not fill me with confidence.
Now you can leave CKOPT in the default state, and it will probably "work". Been there, done that, had a big mess as a result.
The Vittoz mode oscillator amplitude can be marginal, and what you'll see there is occasional odd behaviour like occasional skipped instructions, or baud rates that are a little bit slower than they should be, or if you're really lucky it will just not run.