I've been wondering for a long time how and why to break the rule of thirds. With this shot, you've provided me an answer. Here, you've set the horizon near the center of the shot, and it works because you've created a mirror theme, but with left to right reversal: to my eye, the rocks mirror the clouds in the opposite corners. I doubt that this effect would work as well with a standard rule of thirds placement.
To have strengthened this shot at capture, I think that had you used a polarizing filter, you could have brought out some of the detail of the underwater structures in the lower right of the shot to accentuate the above-water rock. However, maybe you didn't want that. As the shot stands, I think that some contrast adjustment/dodge/burn would help the lower right of the shot, perhaps also with a saturation boost there. Also, emphasizing the horizon with a burn of the bording land might better organize the compositional elements. Finally, right now, there's a lot of similar looking blue, which initially comes across as a bit flat.
Overall, a great effort.
John
