Life in the ocean

From the shores or from a boat, the sea looks like a huge mass of uniform, inky blue water. It is not so actually. Life in the sea is amazingly different at different depths. From the surface to a few feet  below, the ocean is a sunlit world, that changes from day to night. Below this, the ocean becomes cold, dim, and unchanging. And thousands of meters below the surface, the ocean is a region of near-freezing temperatures, crushing pressure, and complete darkness.