As Chris mentions, there is definitely some sort of ghosting caused by movement here. If the camera was on a tripod and it was very windy, this could account for it or, if you just used the shutter release, rather than a remote or timer, you will cause movement by depressing the button with your finger.
What I also noticed is that the sky is blown out and you have gradation of grey tones in the clouds. To avoid this in future, you could either use automatic bracketing if the camera has that feature or take a series of shots, some exposing for the pebbles in the foreground, then some for the sky and reflection in the sea. You can later combine the images to produce a much more detailed final result.
If your camera does not have bracketing I'd do the following:
* Make sure you are shooting in RAW format, not JPEG.
* Position the camera on the tripod and frame your shot
* Set the camera to aperture priority mode
* Select the F value to f/22 again (higher the f/#, the smaller the aperture, the greater the DOF)
* Enable shutter delay so avoid mirror slap
* Use the self timer, setting it to about 10 sec
* Put the camera into manual focus and focus about 1/3 of the way into the frame
* Take a shot and see how the pebbles are exposed. If you're satisfied, make a note of the shutter speed in the EXIF data
* Switch from aperture priority mode to full manual mode.
* Set the aperture to f/22 and the shutter speed to the same as in the EXIF data (In this case 2 seconds).
* Now increase the shutter speed from 2 sec to 1.6 sec and take a picture.
* Repeat this process of reducing the shutter by one incriment each time, until your sky is nicely exposed.
What you should be left with (after discounting all the additional "test" exposures), will be two images. One for your pebbled area and one for your sky/sea reflection. These you can combine in post processing by blending the two images together in different layers iin photoshop or whatever software you are using. You can of course blend more than two images together. You may find that the pebbles are perfect in one exposure, the wall in another and the sky/reflection in a 3rd.
If you wanted a really milky sea, that would be the time to fit that ND filter to the front of the lens that you mentioined in the impulse buying thread

. The above process will be exactly the same, except that your shutter speeds would be much slower, as the ND filter reduces x amount of stops of light, depending on its strength. Expose for the pebbles, then expose for other elements like the sky.