Understanding the nature of ocean life and the patterns of its diversity represents a difficult challenge. Not only are there technical difficulties involved with studying life under water (high pressure, need for oxygen tanks, lack of light), there is an urgency to develop a greater understanding of marine life as links between ocean processes and the larger patterns of terrestrial life become more well known. Our current understanding of oceanic life is based on three principal concepts: size, complexity, and spatial distribution.

Our knowledge about the size of the ocean's domain is grounded in three great discoveries of the past few centuries. When Magellan first circumnavigated the earth he inadvertently found that the oceans were a continuous water body, rather than a series of discrete bodies of water. Some time later, the encompassing nature of the world oceans was further clarified by...