Diatoms are single-cell algae, which create 20%-50% of the oxygen on earth. Ocean acidification causes the silica shell to melt slower, making them sink to the bottom of the ocean first. As a result, the shallower water is missing silica while the deep water is bountiful with silica, which eventually causes a decline in their numbers.
Photo by: https://commons.wikimedia.org/wiki/File:Marine_diatoms_SEM2.jpg
