One of my seo partners decided to change up some of the code on the header of my site. Apparently the only change was adding the "link=rel canonical" tag to the home page, and removing it from all other posts that had something similar. I awoke the next day to the horror of seeing all my keyword rankings drop about 15 spots (and I was on 1st page for 8 of them)! All those rankings I worked so hard on for months...gone... pretty discouraging to say the least. Does anyone know why one little change with this tag can have such effect? Is there anyway to reverse or fix it?
This tag allows one webmaster to indicate under what exact URL he wants one page to be indexed, even if the same content or variations are available under different addresses. It allows search engines to eliminate "duplicate content".