James, thanks for the tip, I didn't know about it and will definitely try next time.
Interceptor121:
It would make absolutely no sence to use a spot meter because the scenes are relatively flat lit.
Also, any camera's meter is calibrated to expose for 18% grey, thus with any camera you would ether shoot in manual to get the exposure that you want, or would pick aperture or shutter priority and use compensation.
Now, given my experience, underwater conditions, alignment of the moon and stars I chose to use the aperture priority and compensation, given that I shot these in raw and post processed them I. Could have went with any combination of exposures, the ones I chose or the ones you suggested.
Whilst your exposures would have worked, I dont feel that they are much off from what the camera chose and noise difference between iso 200 and 320 is negligeable.
If I wanted perfect exposures I would've shot in manual, since I wanted to relax and work on the pictures later I chose aperture priority.