Just because something has been published doesn't mean that it can never again be produced through a separate media. Look at the numerous bloggers who have gone on to have book deals come out of their blogs and the audiences who followed them. I am guessing, since I'm not in the legal rights department of publishing, but I believe having your stuff online, especially on your personal blog, does nothing to your ownership of the rights connected to those poems. You have the ability to do with them what you will. They're your intellectual property, and if you want to bundle them up later on and make a book of poems out of them, there should be nothing stopping you. It's kind of the same approach with short stories, for instance. A lot of writers don't write short stories all at once and make a single book out of it...many of those stories are written over a longer period of time, often individually sold to magazines and ezines. But the rights for those stories eventually revert to the author after a certain time (or they should) and so the author can decide to either re-sell them to another magazine, one that does reprints, or perhaps you can gather those stories and publish them all at once in an acclaimed short story collection.
Long post made short: I personally wouldn't worry about taking down all your posted poetry. It's not going to invalidate future publishing attempts on your part.
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