As land-based creatures, we often underestimate how much of the Earth is water, and specifically salt-water. About 71% of the Earth’s surface is ocean, but the seas of the world comprise by far the greatest amount of inhabitable environment--about 300 times that of land. Small wonder that the waters from which life arose are teeming with a variety of environments and organisms.

The study of ocean organisms and their environment began about one hundred years ago when Karl Moebius, a fisheries biologist, recognized circumstances like an oyster bed as a natural entity, and proposed the word "biocoenosis." In about 1866 Ernst Haeckel (1834-1919) developed the idea of ecology and ecosystems. Ecosystems in the ocean are quite varied, from estuaries to far off-shore regions, and from the surface to the cold, dark depths of the ocean. Oceanographers divide the ocean into zones based on these differences, and study the...