This photo is of an old boat wreck. However, when I saw this I immediately thought of the remains of a large animal; its backbone decaying on the rocks after being washed up by the sea. The black and white sets the scene whereas colour would have added another dimension that would have taken away from the mood. The different shades of pebbles helps to lead the eye to the image and creates some nice contrast.
This image also works well in black and white. However, colour could have worked here too. The photo was taken during a storm so the day was quite windy. The black and white really brings out the feeling of the storm. I also like the different shades of grey along the beach, the blocks of frozen sand that lead the eye into the picture and the spray coming off the surf. Lovely.