If you wrote it (not copied, with or without modification), it is already copyrighted from the moment you commit a draft to a durable medium (handwritten or typed draft, computer document, internet post, etc). You don't have to register it for it to be protected under copyright law. Every writer should know the basics of copyright law.
[duped/adapted from my response to your other thread] you don't 'copyright' anything... what you write is copyrighted automatically, from the moment it's completed and exists in a tangible form... all that's done after that is to 'register' the existing copyright... and that's not usually done till you have a publisher and they take care of it... it has nothing to do with posting your work, or submitting it to competitions, which you should definitely NOT do, if you hope to ever have it published... an exception is screenwriting, as scripts are often registered/archived with wga... if you're a lyricist/songwriter, it's also wise to register your work before sending out demos or submitting lyrics to publishers or artists... you should learn the ins and outs of this very vital part of the business end of writing here: www.copyright.gov
I guess this is a related question. If you submit a short story to a competition such as this, could you also self-publish that story as part of an ebook on, for instance, Kindle? And if it depends on the competition, what are the rules about that for this competition? Cheers.
It depends on the rules Well, Daniel's post announcing the contest says that the winning entry will be published in the e-zine, so there's nothing particular about exclusivity there. If you wanted to double-check, you might want to PM him, but from a legal standpoint I can't see anything stopping you self-publishing it yourself. With most short story venues, all that is needed in terms of rights by the publisher is the rights to publish it, and a period of exclusivity (usually a year from publication), within which you won't publish it anywhere else.