If someone writes a post for my blog, who owns the copyright?

I have been running a wordpress.org blog as a website for over a year now.

At the bottom of the website, it clearly states Copyright © 2012-13 Link Dead Gaming

I had an author writing stories from the site, and he recently left. I do not want to delete his posts, but am not sure if I own the copyright, or he does.

Any help is appreciated.