How to close this ssh tunnel?

I opened a ssh tunnel as described in this post: https://stackoverflow.com/questions/2807118/zend-db-how-to-connect-to-a-mysql-database-over-ssh-tunnel But now I don't know what I actually did. Does this command affect anything on the server? And how do I close this tunnel, because now I can't use my local mysql properly. I use OSX Lion and the server runs on Ubuntu 11.10.