I decided to look into it since I'm going to release a few ebooks within the next few weeks under a pseudonym.
https://www.createspace.com/en/community/thread/4292
You can use a pseudonym. This person suggests that if you do so, you note it in a copyright registration.
I'm going to use my real name, because I don't mind people knowing my real name and it seems easier.
Here's the govs page:
http://www.copyright.gov/fls/fl101.html