What are the differences between the One Piece anime and manga? Recently I started watching the One Piece anime and noticed some differences in the story line  than were present in the manga, and I was wondering if there was a huge divergence in the anime over the manga like with Black Butler, or more like slight differences in plot like with Fullmetal Alchemist: Brotherhood.
The anime and manga closely resemble one another.

This is mainly because the mangaka, Eiichiro Oda actually actively participates into the animation process. So whenever they want a filler episode, they will contact Eiichiro Oda for confirmation, and he would either approve or reject it. 

I believe the only deviations there were was some part in the beginning of the anime that did not totally follow the manga, and ace's tattoo. Which later on got adapted in the manga as well, so not sure how much that would count as a difference.